Implement email alerts

I don't have time to manage a community 😩

.dockerignore

@@ -1,3 +1,7 @@
-example
+.examples
+Dockerfile
 .github
 .idea
+.git
+web/app
+*.db

.examples/docker-compose-grafana-prometheus/config.yaml

@@ -1,15 +1,16 @@
 metrics: true
-services:
-  - name: TwiNNatioN
-    url: https://twinnation.org/health
-    interval: 10s
+endpoints:
+  - name: website
+    url: https://twin.sh/health
+    interval: 30s
     conditions:
       - "[STATUS] == 200"
-  - name: GitHub
+  - name: github
     url: https://api.github.com/healthz
+    interval: 5m
     conditions:
       - "[STATUS] == 200"
-  - name: Example
+  - name: example
     url: https://example.com/
     conditions:
       - "[STATUS] == 200"

.examples/docker-compose-grafana-prometheus/docker-compose.yml

@@ -1,12 +1,11 @@
-version: '3.7'
-
+version: "3.9"
 services:
   gatus:
     container_name: gatus
     image: twinproduction/gatus
     restart: always
     ports:
-      - 8080:8080
+      - "8080:8080"
     volumes:
       - ./config.yaml:/config/config.yaml
     networks:
@@ -18,7 +17,7 @@ services:
     restart: always
     command: --config.file=/etc/prometheus/prometheus.yml
     ports:
-      - 9090:9090
+      - "9090:9090"
     volumes:
       - ./prometheus/prometheus.yml:/etc/prometheus/prometheus.yml
     networks:
@@ -31,7 +30,7 @@ services:
     environment:
       GF_SECURITY_ADMIN_PASSWORD: secret
     ports:
-      - 3000:3000
+      - "3000:3000"
     volumes:
       - ./grafana/grafana.ini/:/etc/grafana/grafana.ini:ro
       - ./grafana/provisioning/:/etc/grafana/provisioning/:ro

.examples/docker-compose-grafana-prometheus/grafana/provisioning/dashboards/main.json

@@ -58,9 +58,9 @@
       "steppedLine": false,
       "targets": [
         {
-          "expr": "sum(rate(gatus_tasks[30s])) by (service)",
+          "expr": "sum(rate(gatus_tasks[30s])) by (endpoint)",
           "interval": "30s",
-          "legendFormat": "{{service}}",
+          "legendFormat": "{{endpoint}}",
           "refId": "A"
         }
       ],
@@ -145,9 +145,9 @@
       "steppedLine": false,
       "targets": [
         {
-          "expr": "sum(rate(gatus_tasks{success=\"false\"}[30s])) by (service)",
+          "expr": "sum(rate(gatus_tasks{success=\"false\"}[30s])) by (endpoint)",
           "interval": "30s",
-          "legendFormat": "{{service}}",
+          "legendFormat": "{{endpoint}}",
           "refId": "A"
         }
       ],
@@ -232,10 +232,10 @@
       "steppedLine": false,
       "targets": [
         {
-          "expr": "sum(rate(gatus_tasks{success=\"true\"}[30s])) by (service)",
+          "expr": "sum(rate(gatus_tasks{success=\"true\"}[30s])) by (endpoint)",
           "instant": false,
           "interval": "30s",
-          "legendFormat": "{{service}}",
+          "legendFormat": "{{endpoint}}",
           "refId": "A"
         }
       ],

.examples/docker-compose-mattermost/config.yaml

@@ -0,0 +1,16 @@
+alerting:
+  mattermost:
+    webhook-url: "http://mattermost:8065/hooks/tokengoeshere"
+    insecure: true
+
+endpoints:
+  - name: example
+    url: https://example.org
+    interval: 1m
+    alerts:
+      - type: mattermost
+        enabled: true
+        description: "health check failed 3 times in a row"
+        send-on-resolved: true
+    conditions:
+      - "[STATUS] == 200"

.examples/docker-compose-mattermost/docker-compose.yml

@@ -0,0 +1,23 @@
+version: "3.9"
+services:
+  gatus:
+    container_name: gatus
+    image: twinproduction/gatus:latest
+    ports:
+      - "8080:8080"
+    volumes:
+      - ./config.yaml:/config/config.yaml
+    networks:
+      - default
+
+  mattermost:
+    container_name: mattermost
+    image: mattermost/mattermost-preview:5.26.0
+    ports:
+      - "8065:8065"
+    networks:
+      - default
+
+networks:
+  default:
+    driver: bridge

.examples/docker-compose-postgres-storage/config.yaml

@@ -0,0 +1,42 @@
+storage:
+  type: postgres
+  path: "postgres://username:password@postgres:5432/gatus?sslmode=disable"
+
+endpoints:
+  - name: back-end
+    group: core
+    url: "https://example.org/"
+    interval: 5m
+    conditions:
+      - "[STATUS] == 200"
+      - "[CERTIFICATE_EXPIRATION] > 48h"
+
+  - name: monitoring
+    group: internal
+    url: "https://example.org/"
+    interval: 5m
+    conditions:
+      - "[STATUS] == 200"
+
+  - name: nas
+    group: internal
+    url: "https://example.org/"
+    interval: 5m
+    conditions:
+      - "[STATUS] == 200"
+
+  - name: example-dns-query
+    url: "8.8.8.8" # Address of the DNS server to use
+    interval: 5m
+    dns:
+      query-name: "example.com"
+      query-type: "A"
+    conditions:
+      - "[BODY] == 93.184.216.34"
+      - "[DNS_RCODE] == NOERROR"
+
+  - name: icmp-ping
+    url: "icmp://example.org"
+    interval: 1m
+    conditions:
+      - "[CONNECTED] == true"

.examples/docker-compose-postgres-storage/docker-compose.yml

@@ -0,0 +1,29 @@
+version: "3.9"
+services:
+  postgres:
+    image: postgres
+    volumes:
+      - ./data/db:/var/lib/postgresql/data
+    ports:
+      - "5432:5432"
+    environment:
+      - POSTGRES_DB=gatus
+      - POSTGRES_USER=username
+      - POSTGRES_PASSWORD=password
+    networks:
+      - web
+
+  gatus:
+    image: twinproduction/gatus:latest
+    restart: always
+    ports:
+      - "8080:8080"
+    volumes:
+      - ./config.yaml:/config/config.yaml
+    networks:
+      - web
+    depends_on:
+      - postgres
+
+networks:
+  web:

.examples/docker-compose-sqlite-storage/config.yaml

@@ -0,0 +1,42 @@
+storage:
+  type: sqlite
+  path: /data/data.db
+
+endpoints:
+  - name: back-end
+    group: core
+    url: "https://example.org/"
+    interval: 5m
+    conditions:
+      - "[STATUS] == 200"
+      - "[CERTIFICATE_EXPIRATION] > 48h"
+
+  - name: monitoring
+    group: internal
+    url: "https://example.org/"
+    interval: 5m
+    conditions:
+      - "[STATUS] == 200"
+
+  - name: nas
+    group: internal
+    url: "https://example.org/"
+    interval: 5m
+    conditions:
+      - "[STATUS] == 200"
+
+  - name: example-dns-query
+    url: "8.8.8.8" # Address of the DNS server to use
+    interval: 5m
+    dns:
+      query-name: "example.com"
+      query-type: "A"
+    conditions:
+      - "[BODY] == 93.184.216.34"
+      - "[DNS_RCODE] == NOERROR"
+
+  - name: icmp-ping
+    url: "icmp://example.org"
+    interval: 1m
+    conditions:
+      - "[CONNECTED] == true"

.examples/docker-compose-sqlite-storage/docker-compose.yml

@@ -0,0 +1,9 @@
+version: "3.9"
+services:
+  gatus:
+    image: twinproduction/gatus:latest
+    ports:
+      - "8080:8080"
+    volumes:
+      - ./config.yaml:/config/config.yaml
+      - ./data:/data/

.examples/docker-compose/config.yaml

@@ -1,6 +1,6 @@
-services:
+endpoints:
   - name: example
-    url: http://example.org
+    url: https://example.org
     interval: 30s
     conditions:
       - "[STATUS] == 200"

.examples/docker-compose/docker-compose.yml

@@ -0,0 +1,8 @@
+version: "3.8"
+services:
+  gatus:
+    image: twinproduction/gatus:latest
+    ports:
+      - 8080:8080
+    volumes:
+      - ./config.yaml:/config/config.yaml

.examples/docker-minimal/config.yaml

@@ -0,0 +1,6 @@
+endpoints:
+  - name: example
+    url: https://example.org
+    interval: 30s
+    conditions:
+      - "[STATUS] == 200"

.examples/kubernetes/gatus.yaml

@@ -1,22 +1,43 @@
 apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: gatus
+  namespace: kube-system
 data:
   config.yaml: |
     metrics: true
-    services:
-      - name: TwiNNatioN
-        url: https://twinnation.org/health
-        interval: 1m
+    endpoints:
+      - name: website
+        url: https://twin.sh/health
+        interval: 5m
         conditions:
           - "[STATUS] == 200"
-      - name: GitHub
+          - "[BODY].status == UP"
+
+      - name: github
         url: https://api.github.com/healthz
+        interval: 5m
         conditions:
           - "[STATUS] == 200"
-      - name: Example
+
+      - name: cat-fact
+        url: "https://cat-fact.herokuapp.com/facts/random"
+        interval: 5m
+        conditions:
+          - "[STATUS] == 200"
+          - "[BODY].deleted == false"
+          - "len([BODY].text) > 0"
+          - "[BODY].text == pat(*cat*)"
+          - "[STATUS] == pat(2*)"
+          - "[CONNECTED] == true"
+
+      - name: example
         url: https://example.com/
         conditions:
           - "[STATUS] == 200"
-kind: ConfigMap
+---
+apiVersion: v1
+kind: ServiceAccount
 metadata:
   name: gatus
   namespace: kube-system
@@ -30,14 +51,16 @@ spec:
   replicas: 1
   selector:
     matchLabels:
-      k8s-app: gatus
+      app: gatus
   template:
     metadata:
       labels:
-        k8s-app: gatus
+        app: gatus
       name: gatus
       namespace: kube-system
     spec:
+      serviceAccountName: gatus
+      terminationGracePeriodSeconds: 5
       containers:
         - image: twinproduction/gatus
           imagePullPolicy: IfNotPresent
@@ -48,11 +71,11 @@ spec:
               protocol: TCP
           resources:
             limits:
-              cpu: 50m
-              memory: 50M
+              cpu: 250m
+              memory: 100M
             requests:
-              cpu: 20m
-              memory: 20M
+              cpu: 50m
+              memory: 30M
           volumeMounts:
             - mountPath: /config
               name: gatus-config
@@ -73,4 +96,4 @@ spec:
       protocol: TCP
       targetPort: 8080
   selector:
-    k8s-app: gatus
+    app: gatus

.gitattributes

@@ -0,0 +1 @@
+* text=auto eol=lf

.github/FUNDING.yml

@@ -0,0 +1 @@
+github: [TwiN]

.github/assets/gatus-diagram.drawio

@@ -0,0 +1 @@
+<mxfile host="app.diagrams.net" modified="2021-09-12T22:49:28.336Z" agent="5.0 (Windows)" etag="r9FJ6Bphqwq-LaTO-jp3" version="15.0.6" type="device"><diagram id="FBbfVOMCjf6Z2LK8Yagy" name="Page-1">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</diagram></mxfile>

.github/codecov.yml

@@ -0,0 +1,7 @@
+ignore:
+  - "watchdog/watchdog.go"
+  - "storage/store/sql/specific_postgres.go" # Can't test for postgres
+
+coverage:
+  status:
+    patch: off

.github/workflows/build.yml

@@ -0,0 +1,33 @@
+name: build
+on:
+  pull_request:
+    paths-ignore:
+      - '*.md'
+  push:
+    branches:
+      - master
+    paths-ignore:
+      - '*.md'
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - name: Set up Go
+        uses: actions/setup-go@v2
+        with:
+          go-version: 1.17
+      - name: Check out code into the Go module directory
+        uses: actions/checkout@v2
+      - name: Build binary to make sure it works
+        run: go build -mod vendor
+      - name: Test
+        # We're using "sudo" because one of the tests leverages ping, which requires super-user privileges.
+        # As for the 'env "PATH=$PATH" "GOROOT=$GOROOT"', we need it to use the same "go" executable that
+        # was configured by the "Set up Go" step (otherwise, it'd use sudo's "go" executable)
+        run: sudo env "PATH=$PATH" "GOROOT=$GOROOT" go test -mod vendor ./... -race -coverprofile=coverage.txt -covermode=atomic
+      - name: Codecov
+        uses: codecov/codecov-action@v2.1.0
+        with:
+          files: ./coverage.txt

.github/workflows/go.yml

@@ -1,34 +0,0 @@
-name: Go
-on: [push]
-jobs:
-  build-112:
-    name: Build with Go 1.12
-    runs-on: ubuntu-latest
-    steps:
-    - name: Set up Go 1.12
-      uses: actions/setup-go@v1
-      with:
-        go-version: 1.12
-      id: go
-    - name: Check out code into the Go module directory
-      uses: actions/checkout@v1
-    - name: Test
-      run: go test -mod vendor ./...
-    - name: Build
-      run: go build -mod vendor
-
-  build-113:
-    name: Build with Go 1.13
-    runs-on: ubuntu-latest
-    steps:
-      - name: Set up Go 1.13
-        uses: actions/setup-go@v1
-        with:
-          go-version: 1.13
-        id: go
-      - name: Check out code into the Go module directory
-        uses: actions/checkout@v1
-      - name: Test
-        run: go test -mod vendor ./...
-      - name: Build
-        run: go build -mod vendor

.github/workflows/publish-latest.yml

@@ -0,0 +1,34 @@
+name: publish-latest
+on:
+  workflow_run:
+    workflows: ["build"]
+    branches: [master]
+    types: [completed]
+jobs:
+  publish-latest:
+    name: Publish latest
+    runs-on: ubuntu-latest
+    if: ${{ github.event.workflow_run.conclusion == 'success' }}
+    timeout-minutes: 30
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v2
+      - name: Get image repository
+        run: echo IMAGE_REPOSITORY=$(echo ${{ secrets.DOCKER_USERNAME }}/${{ github.event.repository.name }} | tr '[:upper:]' '[:lower:]') >> $GITHUB_ENV
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      - name: Login to Docker Registry
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
+      - name: Build and push docker image
+        uses: docker/build-push-action@v2
+        with:
+          platforms: linux/amd64
+          pull: true
+          push: true
+          tags: |
+            ${{ env.IMAGE_REPOSITORY }}:latest

.github/workflows/publish-release.yml

@@ -0,0 +1,33 @@
+name: publish-release
+on:
+  release:
+    types: [published]
+jobs:
+  publish-release:
+    name: Publish release
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v2
+      - name: Get image repository
+        run: echo IMAGE_REPOSITORY=$(echo ${{ secrets.DOCKER_USERNAME }}/${{ github.event.repository.name }} | tr '[:upper:]' '[:lower:]') >> $GITHUB_ENV
+      - name: Get the release
+        run: echo RELEASE=${GITHUB_REF/refs\/tags\//} >> $GITHUB_ENV
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      - name: Login to Docker Registry
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
+      - name: Build and push docker image
+        uses: docker/build-push-action@v2
+        with:
+          platforms: linux/amd64,linux/arm/v6,linux/arm/v7,linux/arm64
+          pull: true
+          push: true
+          tags: |
+            ${{ env.IMAGE_REPOSITORY }}:${{ env.RELEASE }}

.gitignore

@@ -1,4 +1,8 @@
-bin
 .idea
-test.db
-daily.db
+.vscode
+gatus
+db.db
+config/config.yml
+db.db-shm
+db.db-wal
+memory.db

Dockerfile

@@ -1,16 +1,20 @@
 # Build the go application into a binary
 FROM golang:alpine as builder
-WORKDIR /app
-ADD . ./
-RUN CGO_ENABLED=0 GOOS=linux go build -mod vendor -a -installsuffix cgo -o gatus .
 RUN apk --update add ca-certificates
+WORKDIR /app
+COPY . ./
+RUN CGO_ENABLED=0 GOOS=linux go build -mod vendor -a -installsuffix cgo -o gatus .
+
+# Run Tests inside docker image if you don't have a configured go environment
+#RUN apk update && apk add --virtual build-dependencies build-base gcc
+#RUN go test ./... -mod vendor
 
 # Run the binary on an empty container
 FROM scratch
 COPY --from=builder /app/gatus .
 COPY --from=builder /app/config.yaml ./config/config.yaml
-COPY --from=builder /app/static static/
+COPY --from=builder /app/web/static ./web/static
 COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt
 ENV PORT=8080
 EXPOSE ${PORT}
-ENTRYPOINT ["/gatus"]
+ENTRYPOINT ["/gatus"]

LICENSE

@@ -186,7 +186,7 @@
       same "printed page" as the copyright notice for easier
       identification within third-party archives.
 
-   Copyright [yyyy] [name of copyright owner]
+   Copyright 2021 TwiN
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
@@ -199,3 +199,4 @@
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
+

Makefile

@@ -0,0 +1,37 @@
+BINARY=gatus
+
+install:
+	go build -mod vendor -o $(BINARY) .
+
+run:
+	GATUS_CONFIG_FILE=./config.yaml ./$(BINARY)
+
+clean:
+	rm $(BINARY)
+
+test:
+	sudo go test ./alerting/... ./client/... ./config/... ./controller/... ./core/... ./jsonpath/... ./pattern/... ./security/... ./storage/... ./util/... ./watchdog/... -cover
+
+
+##########
+# Docker #
+##########
+
+docker-build:
+	docker build -t twinproduction/gatus:latest .
+
+docker-run:
+	docker run -p 8080:8080 --name gatus twinproduction/gatus:latest
+
+docker-build-and-run: docker-build docker-run
+
+
+#############
+# Front end #
+#############
+
+frontend-build:
+	npm --prefix web/app run build
+
+frontend-run:
+	npm --prefix web/app run serve

alerting/alert/alert.go

@@ -0,0 +1,69 @@
+package alert
+
+// Alert is a core.Endpoint's alert configuration
+type Alert struct {
+	// Type of alert (required)
+	Type Type `yaml:"type"`
+
+	// Enabled defines whether the alert is enabled
+	//
+	// This is a pointer, because it is populated by YAML and we need to know whether it was explicitly set to a value
+	// or not for provider.ParseWithDefaultAlert to work.
+	Enabled *bool `yaml:"enabled,omitempty"`
+
+	// FailureThreshold is the number of failures in a row needed before triggering the alert
+	FailureThreshold int `yaml:"failure-threshold"`
+
+	// Description of the alert. Will be included in the alert sent.
+	//
+	// This is a pointer, because it is populated by YAML and we need to know whether it was explicitly set to a value
+	// or not for provider.ParseWithDefaultAlert to work.
+	Description *string `yaml:"description"`
+
+	// SendOnResolved defines whether to send a second notification when the issue has been resolved
+	//
+	// This is a pointer, because it is populated by YAML and we need to know whether it was explicitly set to a value
+	// or not for provider.ParseWithDefaultAlert to work. Use Alert.IsSendingOnResolved() for a non-pointer
+	SendOnResolved *bool `yaml:"send-on-resolved"`
+
+	// SuccessThreshold defines how many successful executions must happen in a row before an ongoing incident is marked as resolved
+	SuccessThreshold int `yaml:"success-threshold"`
+
+	// ResolveKey is an optional field that is used by some providers (i.e. PagerDuty's dedup_key) to resolve
+	// ongoing/triggered incidents
+	ResolveKey string `yaml:"-"`
+
+	// Triggered is used to determine whether an alert has been triggered. When an alert is resolved, this value
+	// should be set back to false. It is used to prevent the same alert from going out twice.
+	//
+	// This value should only be modified if the provider.AlertProvider's Send function does not return an error for an
+	// alert that hasn't been triggered yet. This doubles as a lazy retry. The reason why this behavior isn't also
+	// applied for alerts that are already triggered and has become "healthy" again is to prevent a case where, for
+	// some reason, the alert provider always returns errors when trying to send the resolved notification
+	// (SendOnResolved).
+	Triggered bool `yaml:"-"`
+}
+
+// GetDescription retrieves the description of the alert
+func (alert Alert) GetDescription() string {
+	if alert.Description == nil {
+		return ""
+	}
+	return *alert.Description
+}
+
+// IsEnabled returns whether an alert is enabled or not
+func (alert Alert) IsEnabled() bool {
+	if alert.Enabled == nil {
+		return false
+	}
+	return *alert.Enabled
+}
+
+// IsSendingOnResolved returns whether an alert is sending on resolve or not
+func (alert Alert) IsSendingOnResolved() bool {
+	if alert.SendOnResolved == nil {
+		return false
+	}
+	return *alert.SendOnResolved
+}

alerting/alert/alert_test.go

@@ -0,0 +1,36 @@
+package alert
+
+import "testing"
+
+func TestAlert_IsEnabled(t *testing.T) {
+	if (Alert{Enabled: nil}).IsEnabled() {
+		t.Error("alert.IsEnabled() should've returned false, because Enabled was set to nil")
+	}
+	if value := false; (Alert{Enabled: &value}).IsEnabled() {
+		t.Error("alert.IsEnabled() should've returned false, because Enabled was set to false")
+	}
+	if value := true; !(Alert{Enabled: &value}).IsEnabled() {
+		t.Error("alert.IsEnabled() should've returned true, because Enabled was set to true")
+	}
+}
+
+func TestAlert_GetDescription(t *testing.T) {
+	if (Alert{Description: nil}).GetDescription() != "" {
+		t.Error("alert.GetDescription() should've returned an empty string, because Description was set to nil")
+	}
+	if value := "description"; (Alert{Description: &value}).GetDescription() != value {
+		t.Error("alert.GetDescription() should've returned false, because Description was set to 'description'")
+	}
+}
+
+func TestAlert_IsSendingOnResolved(t *testing.T) {
+	if (Alert{SendOnResolved: nil}).IsSendingOnResolved() {
+		t.Error("alert.IsSendingOnResolved() should've returned false, because SendOnResolved was set to nil")
+	}
+	if value := false; (Alert{SendOnResolved: &value}).IsSendingOnResolved() {
+		t.Error("alert.IsSendingOnResolved() should've returned false, because SendOnResolved was set to false")
+	}
+	if value := true; !(Alert{SendOnResolved: &value}).IsSendingOnResolved() {
+		t.Error("alert.IsSendingOnResolved() should've returned true, because SendOnResolved was set to true")
+	}
+}

alerting/alert/type.go

@@ -0,0 +1,37 @@
+package alert
+
+// Type is the type of the alert.
+// The value will generally be the name of the alert provider
+type Type string
+
+const (
+	// TypeCustom is the Type for the custom alerting provider
+	TypeCustom Type = "custom"
+
+	// TypeDiscord is the Type for the discord alerting provider
+	TypeDiscord Type = "discord"
+
+	// TypeEmail is the Type for the email alerting provider
+	TypeEmail Type = "email"
+
+	// TypeMattermost is the Type for the mattermost alerting provider
+	TypeMattermost Type = "mattermost"
+
+	// TypeMessagebird is the Type for the messagebird alerting provider
+	TypeMessagebird Type = "messagebird"
+
+	// TypePagerDuty is the Type for the pagerduty alerting provider
+	TypePagerDuty Type = "pagerduty"
+
+	// TypeSlack is the Type for the slack alerting provider
+	TypeSlack Type = "slack"
+
+	// TypeTeams is the Type for the teams alerting provider
+	TypeTeams Type = "teams"
+
+	// TypeTelegram is the Type for the telegram alerting provider
+	TypeTelegram Type = "telegram"
+
+	// TypeTwilio is the Type for the twilio alerting provider
+	TypeTwilio Type = "twilio"
+)

alerting/config.go

@@ -0,0 +1,116 @@
+package alerting
+
+import (
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/alerting/provider"
+	"github.com/TwiN/gatus/v3/alerting/provider/custom"
+	"github.com/TwiN/gatus/v3/alerting/provider/discord"
+	"github.com/TwiN/gatus/v3/alerting/provider/email"
+	"github.com/TwiN/gatus/v3/alerting/provider/mattermost"
+	"github.com/TwiN/gatus/v3/alerting/provider/messagebird"
+	"github.com/TwiN/gatus/v3/alerting/provider/pagerduty"
+	"github.com/TwiN/gatus/v3/alerting/provider/slack"
+	"github.com/TwiN/gatus/v3/alerting/provider/teams"
+	"github.com/TwiN/gatus/v3/alerting/provider/telegram"
+	"github.com/TwiN/gatus/v3/alerting/provider/twilio"
+)
+
+// Config is the configuration for alerting providers
+type Config struct {
+	// Custom is the configuration for the custom alerting provider
+	Custom *custom.AlertProvider `yaml:"custom,omitempty"`
+
+	// Discord is the configuration for the discord alerting provider
+	Discord *discord.AlertProvider `yaml:"discord,omitempty"`
+
+	// Email is the configuration for the email alerting provider
+	Email *email.AlertProvider `yaml:"email,omitempty"`
+
+	// Mattermost is the configuration for the mattermost alerting provider
+	Mattermost *mattermost.AlertProvider `yaml:"mattermost,omitempty"`
+
+	// Messagebird is the configuration for the messagebird alerting provider
+	Messagebird *messagebird.AlertProvider `yaml:"messagebird,omitempty"`
+
+	// PagerDuty is the configuration for the pagerduty alerting provider
+	PagerDuty *pagerduty.AlertProvider `yaml:"pagerduty,omitempty"`
+
+	// Slack is the configuration for the slack alerting provider
+	Slack *slack.AlertProvider `yaml:"slack,omitempty"`
+
+	// Teams is the configuration for the teams alerting provider
+	Teams *teams.AlertProvider `yaml:"teams,omitempty"`
+
+	// Telegram is the configuration for the telegram alerting provider
+	Telegram *telegram.AlertProvider `yaml:"telegram,omitempty"`
+
+	// Twilio is the configuration for the twilio alerting provider
+	Twilio *twilio.AlertProvider `yaml:"twilio,omitempty"`
+}
+
+// GetAlertingProviderByAlertType returns an provider.AlertProvider by its corresponding alert.Type
+func (config Config) GetAlertingProviderByAlertType(alertType alert.Type) provider.AlertProvider {
+	switch alertType {
+	case alert.TypeCustom:
+		if config.Custom == nil {
+			// Since we're returning an interface, we need to explicitly return nil, even if the provider itself is nil
+			return nil
+		}
+		return config.Custom
+	case alert.TypeDiscord:
+		if config.Discord == nil {
+			// Since we're returning an interface, we need to explicitly return nil, even if the provider itself is nil
+			return nil
+		}
+		return config.Discord
+	case alert.TypeEmail:
+		if config.Email == nil {
+			// Since we're returning an interface, we need to explicitly return nil, even if the provider itself is nil
+			return nil
+		}
+		return config.Email
+	case alert.TypeMattermost:
+		if config.Mattermost == nil {
+			// Since we're returning an interface, we need to explicitly return nil, even if the provider itself is nil
+			return nil
+		}
+		return config.Mattermost
+	case alert.TypeMessagebird:
+		if config.Messagebird == nil {
+			// Since we're returning an interface, we need to explicitly return nil, even if the provider itself is nil
+			return nil
+		}
+		return config.Messagebird
+	case alert.TypePagerDuty:
+		if config.PagerDuty == nil {
+			// Since we're returning an interface, we need to explicitly return nil, even if the provider itself is nil
+			return nil
+		}
+		return config.PagerDuty
+	case alert.TypeSlack:
+		if config.Slack == nil {
+			// Since we're returning an interface, we need to explicitly return nil, even if the provider itself is nil
+			return nil
+		}
+		return config.Slack
+	case alert.TypeTeams:
+		if config.Teams == nil {
+			// Since we're returning an interface, we need to explicitly return nil, even if the provider itself is nil
+			return nil
+		}
+		return config.Teams
+	case alert.TypeTelegram:
+		if config.Telegram == nil {
+			// Since we're returning an interface, we need to explicitly return nil, even if the provider itself is nil
+			return nil
+		}
+		return config.Telegram
+	case alert.TypeTwilio:
+		if config.Twilio == nil {
+			// Since we're returning an interface, we need to explicitly return nil, even if the provider itself is nil
+			return nil
+		}
+		return config.Twilio
+	}
+	return nil
+}

alerting/provider/custom/custom.go

@@ -0,0 +1,117 @@
+package custom
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"strings"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+)
+
+// AlertProvider is the configuration necessary for sending an alert using a custom HTTP request
+// Technically, all alert providers should be reachable using the custom alert provider
+type AlertProvider struct {
+	URL          string                       `yaml:"url"`
+	Method       string                       `yaml:"method,omitempty"`
+	Body         string                       `yaml:"body,omitempty"`
+	Headers      map[string]string            `yaml:"headers,omitempty"`
+	Placeholders map[string]map[string]string `yaml:"placeholders,omitempty"`
+
+	// ClientConfig is the configuration of the client used to communicate with the provider's target
+	ClientConfig *client.Config `yaml:"client"`
+
+	// DefaultAlert is the default alert configuration to use for endpoints with an alert of the appropriate type
+	DefaultAlert *alert.Alert `yaml:"default-alert"`
+}
+
+// IsValid returns whether the provider's configuration is valid
+func (provider *AlertProvider) IsValid() bool {
+	if provider.ClientConfig == nil {
+		provider.ClientConfig = client.GetDefaultConfig()
+	}
+	return len(provider.URL) > 0 && provider.ClientConfig != nil
+}
+
+// GetAlertStatePlaceholderValue returns the Placeholder value for ALERT_TRIGGERED_OR_RESOLVED if configured
+func (provider *AlertProvider) GetAlertStatePlaceholderValue(resolved bool) string {
+	status := "TRIGGERED"
+	if resolved {
+		status = "RESOLVED"
+	}
+	if _, ok := provider.Placeholders["ALERT_TRIGGERED_OR_RESOLVED"]; ok {
+		if val, ok := provider.Placeholders["ALERT_TRIGGERED_OR_RESOLVED"][status]; ok {
+			return val
+		}
+	}
+	return status
+}
+
+func (provider *AlertProvider) buildHTTPRequest(endpointName, alertDescription string, resolved bool) *http.Request {
+	body := provider.Body
+	providerURL := provider.URL
+	method := provider.Method
+
+	if strings.Contains(body, "[ALERT_DESCRIPTION]") {
+		body = strings.ReplaceAll(body, "[ALERT_DESCRIPTION]", alertDescription)
+	}
+	if strings.Contains(body, "[SERVICE_NAME]") { // XXX: Remove this in v4.0.0
+		body = strings.ReplaceAll(body, "[SERVICE_NAME]", endpointName)
+	}
+	if strings.Contains(body, "[ENDPOINT_NAME]") {
+		body = strings.ReplaceAll(body, "[ENDPOINT_NAME]", endpointName)
+	}
+	if strings.Contains(body, "[ALERT_TRIGGERED_OR_RESOLVED]") {
+		if resolved {
+			body = strings.ReplaceAll(body, "[ALERT_TRIGGERED_OR_RESOLVED]", provider.GetAlertStatePlaceholderValue(true))
+		} else {
+			body = strings.ReplaceAll(body, "[ALERT_TRIGGERED_OR_RESOLVED]", provider.GetAlertStatePlaceholderValue(false))
+		}
+	}
+	if strings.Contains(providerURL, "[ALERT_DESCRIPTION]") {
+		providerURL = strings.ReplaceAll(providerURL, "[ALERT_DESCRIPTION]", alertDescription)
+	}
+	if strings.Contains(providerURL, "[SERVICE_NAME]") { // XXX: Remove this in v4.0.0
+		providerURL = strings.ReplaceAll(providerURL, "[SERVICE_NAME]", endpointName)
+	}
+	if strings.Contains(providerURL, "[ENDPOINT_NAME]") {
+		providerURL = strings.ReplaceAll(providerURL, "[ENDPOINT_NAME]", endpointName)
+	}
+	if strings.Contains(providerURL, "[ALERT_TRIGGERED_OR_RESOLVED]") {
+		if resolved {
+			providerURL = strings.ReplaceAll(providerURL, "[ALERT_TRIGGERED_OR_RESOLVED]", provider.GetAlertStatePlaceholderValue(true))
+		} else {
+			providerURL = strings.ReplaceAll(providerURL, "[ALERT_TRIGGERED_OR_RESOLVED]", provider.GetAlertStatePlaceholderValue(false))
+		}
+	}
+	if len(method) == 0 {
+		method = http.MethodGet
+	}
+	bodyBuffer := bytes.NewBuffer([]byte(body))
+	request, _ := http.NewRequest(method, providerURL, bodyBuffer)
+	for k, v := range provider.Headers {
+		request.Header.Set(k, v)
+	}
+	return request
+}
+
+func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) error {
+	request := provider.buildHTTPRequest(endpoint.Name, alert.GetDescription(), resolved)
+	response, err := client.GetHTTPClient(provider.ClientConfig).Do(request)
+	if err != nil {
+		return err
+	}
+	if response.StatusCode > 399 {
+		body, _ := ioutil.ReadAll(response.Body)
+		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
+	}
+	return err
+}
+
+// GetDefaultAlert returns the provider's default alert configuration
+func (provider AlertProvider) GetDefaultAlert() *alert.Alert {
+	return provider.DefaultAlert
+}

alerting/provider/custom/custom_test.go

@@ -0,0 +1,212 @@
+package custom
+
+import (
+	"io/ioutil"
+	"net/http"
+	"testing"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+	"github.com/TwiN/gatus/v3/test"
+)
+
+func TestAlertProvider_IsValid(t *testing.T) {
+	invalidProvider := AlertProvider{URL: ""}
+	if invalidProvider.IsValid() {
+		t.Error("provider shouldn't have been valid")
+	}
+	validProvider := AlertProvider{URL: "https://example.com"}
+	if !validProvider.IsValid() {
+		t.Error("provider should've been valid")
+	}
+}
+
+func TestAlertProvider_Send(t *testing.T) {
+	defer client.InjectHTTPClient(nil)
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name             string
+		Provider         AlertProvider
+		Alert            alert.Alert
+		Resolved         bool
+		MockRoundTripper test.MockRoundTripper
+		ExpectedError    bool
+	}{
+		{
+			Name:     "triggered",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "triggered-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+		{
+			Name:     "resolved",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "resolved-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			client.InjectHTTPClient(&http.Client{Transport: scenario.MockRoundTripper})
+			err := scenario.Provider.Send(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if scenario.ExpectedError && err == nil {
+				t.Error("expected error, got none")
+			}
+			if !scenario.ExpectedError && err != nil {
+				t.Error("expected no error, got", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_buildHTTPRequestWhenResolved(t *testing.T) {
+	const (
+		ExpectedURL  = "https://example.com/endpoint-name?event=RESOLVED&description=alert-description"
+		ExpectedBody = "endpoint-name,alert-description,RESOLVED"
+	)
+	customAlertProvider := &AlertProvider{
+		URL:     "https://example.com/[ENDPOINT_NAME]?event=[ALERT_TRIGGERED_OR_RESOLVED]&description=[ALERT_DESCRIPTION]",
+		Body:    "[ENDPOINT_NAME],[ALERT_DESCRIPTION],[ALERT_TRIGGERED_OR_RESOLVED]",
+		Headers: nil,
+	}
+	request := customAlertProvider.buildHTTPRequest("endpoint-name", "alert-description", true)
+	if request.URL.String() != ExpectedURL {
+		t.Error("expected URL to be", ExpectedURL, "was", request.URL.String())
+	}
+	body, _ := ioutil.ReadAll(request.Body)
+	if string(body) != ExpectedBody {
+		t.Error("expected body to be", ExpectedBody, "was", string(body))
+	}
+}
+
+func TestAlertProvider_buildHTTPRequestWhenTriggered(t *testing.T) {
+	const (
+		ExpectedURL  = "https://example.com/endpoint-name?event=TRIGGERED&description=alert-description"
+		ExpectedBody = "endpoint-name,alert-description,TRIGGERED"
+	)
+	customAlertProvider := &AlertProvider{
+		URL:     "https://example.com/[ENDPOINT_NAME]?event=[ALERT_TRIGGERED_OR_RESOLVED]&description=[ALERT_DESCRIPTION]",
+		Body:    "[ENDPOINT_NAME],[ALERT_DESCRIPTION],[ALERT_TRIGGERED_OR_RESOLVED]",
+		Headers: map[string]string{"Authorization": "Basic hunter2"},
+	}
+	request := customAlertProvider.buildHTTPRequest("endpoint-name", "alert-description", false)
+	if request.URL.String() != ExpectedURL {
+		t.Error("expected URL to be", ExpectedURL, "was", request.URL.String())
+	}
+	body, _ := ioutil.ReadAll(request.Body)
+	if string(body) != ExpectedBody {
+		t.Error("expected body to be", ExpectedBody, "was", string(body))
+	}
+}
+
+func TestAlertProvider_buildHTTPRequestWithCustomPlaceholder(t *testing.T) {
+	const (
+		ExpectedURL  = "https://example.com/endpoint-name?event=test&description=alert-description"
+		ExpectedBody = "endpoint-name,alert-description,test"
+	)
+	customAlertProvider := &AlertProvider{
+		URL:     "https://example.com/[ENDPOINT_NAME]?event=[ALERT_TRIGGERED_OR_RESOLVED]&description=[ALERT_DESCRIPTION]",
+		Body:    "[ENDPOINT_NAME],[ALERT_DESCRIPTION],[ALERT_TRIGGERED_OR_RESOLVED]",
+		Headers: nil,
+		Placeholders: map[string]map[string]string{
+			"ALERT_TRIGGERED_OR_RESOLVED": {
+				"RESOLVED": "test",
+			},
+		},
+	}
+	request := customAlertProvider.buildHTTPRequest("endpoint-name", "alert-description", true)
+	if request.URL.String() != ExpectedURL {
+		t.Error("expected URL to be", ExpectedURL, "was", request.URL.String())
+	}
+	body, _ := ioutil.ReadAll(request.Body)
+	if string(body) != ExpectedBody {
+		t.Error("expected body to be", ExpectedBody, "was", string(body))
+	}
+}
+
+func TestAlertProvider_GetAlertStatePlaceholderValueDefaults(t *testing.T) {
+	customAlertProvider := &AlertProvider{
+		URL:          "https://example.com/[ENDPOINT_NAME]?event=[ALERT_TRIGGERED_OR_RESOLVED]&description=[ALERT_DESCRIPTION]",
+		Body:         "[ENDPOINT_NAME],[ALERT_DESCRIPTION],[ALERT_TRIGGERED_OR_RESOLVED]",
+		Headers:      nil,
+		Placeholders: nil,
+	}
+	if customAlertProvider.GetAlertStatePlaceholderValue(true) != "RESOLVED" {
+		t.Error("expected RESOLVED, got", customAlertProvider.GetAlertStatePlaceholderValue(true))
+	}
+	if customAlertProvider.GetAlertStatePlaceholderValue(false) != "TRIGGERED" {
+		t.Error("expected TRIGGERED, got", customAlertProvider.GetAlertStatePlaceholderValue(false))
+	}
+}
+
+func TestAlertProvider_GetDefaultAlert(t *testing.T) {
+	if (AlertProvider{DefaultAlert: &alert.Alert{}}).GetDefaultAlert() == nil {
+		t.Error("expected default alert to be not nil")
+	}
+	if (AlertProvider{DefaultAlert: nil}).GetDefaultAlert() != nil {
+		t.Error("expected default alert to be nil")
+	}
+}
+
+// TestAlertProvider_isBackwardCompatibleWithServiceRename checks if the custom alerting provider still supports
+// service placeholders after the migration from "service" to "endpoint"
+//
+// XXX: Remove this in v4.0.0
+func TestAlertProvider_isBackwardCompatibleWithServiceRename(t *testing.T) {
+	const (
+		ExpectedURL  = "https://example.com/endpoint-name?event=TRIGGERED&description=alert-description"
+		ExpectedBody = "endpoint-name,alert-description,TRIGGERED"
+	)
+	customAlertProvider := &AlertProvider{
+		URL:  "https://example.com/[SERVICE_NAME]?event=[ALERT_TRIGGERED_OR_RESOLVED]&description=[ALERT_DESCRIPTION]",
+		Body: "[SERVICE_NAME],[ALERT_DESCRIPTION],[ALERT_TRIGGERED_OR_RESOLVED]",
+	}
+	request := customAlertProvider.buildHTTPRequest("endpoint-name", "alert-description", false)
+	if request.URL.String() != ExpectedURL {
+		t.Error("expected URL to be", ExpectedURL, "was", request.URL.String())
+	}
+	body, _ := ioutil.ReadAll(request.Body)
+	if string(body) != ExpectedBody {
+		t.Error("expected body to be", ExpectedBody, "was", string(body))
+	}
+}

alerting/provider/discord/discord.go

@@ -0,0 +1,92 @@
+package discord
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+)
+
+// AlertProvider is the configuration necessary for sending an alert using Discord
+type AlertProvider struct {
+	WebhookURL string `yaml:"webhook-url"`
+
+	// DefaultAlert is the default alert configuration to use for endpoints with an alert of the appropriate type
+	DefaultAlert *alert.Alert `yaml:"default-alert"`
+}
+
+// IsValid returns whether the provider's configuration is valid
+func (provider *AlertProvider) IsValid() bool {
+	return len(provider.WebhookURL) > 0
+}
+
+// Send an alert using the provider
+func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) error {
+	buffer := bytes.NewBuffer([]byte(provider.buildRequestBody(endpoint, alert, result, resolved)))
+	request, err := http.NewRequest(http.MethodPost, provider.WebhookURL, buffer)
+	if err != nil {
+		return err
+	}
+	request.Header.Set("Content-Type", "application/json")
+	response, err := client.GetHTTPClient(nil).Do(request)
+	if err != nil {
+		return err
+	}
+	if response.StatusCode > 399 {
+		body, _ := ioutil.ReadAll(response.Body)
+		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
+	}
+	return err
+}
+
+// buildRequestBody builds the request body for the provider
+func (provider *AlertProvider) buildRequestBody(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) string {
+	var message, results string
+	var colorCode int
+	if resolved {
+		message = fmt.Sprintf("An alert for **%s** has been resolved after passing successfully %d time(s) in a row", endpoint.Name, alert.SuccessThreshold)
+		colorCode = 3066993
+	} else {
+		message = fmt.Sprintf("An alert for **%s** has been triggered due to having failed %d time(s) in a row", endpoint.Name, alert.FailureThreshold)
+		colorCode = 15158332
+	}
+	for _, conditionResult := range result.ConditionResults {
+		var prefix string
+		if conditionResult.Success {
+			prefix = ":white_check_mark:"
+		} else {
+			prefix = ":x:"
+		}
+		results += fmt.Sprintf("%s - `%s`\\n", prefix, conditionResult.Condition)
+	}
+	var description string
+	if alertDescription := alert.GetDescription(); len(alertDescription) > 0 {
+		description = ":\\n> " + alertDescription
+	}
+	return fmt.Sprintf(`{
+  "content": "",
+  "embeds": [
+    {
+      "title": ":helmet_with_white_cross: Gatus",
+      "description": "%s%s",
+      "color": %d,
+      "fields": [
+        {
+          "name": "Condition results",
+          "value": "%s",
+          "inline": false
+        }
+      ]
+    }
+  ]
+}`, message, description, colorCode, results)
+}
+
+// GetDefaultAlert returns the provider's default alert configuration
+func (provider AlertProvider) GetDefaultAlert() *alert.Alert {
+	return provider.DefaultAlert
+}

alerting/provider/discord/discord_test.go

@@ -0,0 +1,158 @@
+package discord
+
+import (
+	"encoding/json"
+	"net/http"
+	"testing"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+	"github.com/TwiN/gatus/v3/test"
+)
+
+func TestAlertProvider_IsValid(t *testing.T) {
+	invalidProvider := AlertProvider{WebhookURL: ""}
+	if invalidProvider.IsValid() {
+		t.Error("provider shouldn't have been valid")
+	}
+	validProvider := AlertProvider{WebhookURL: "http://example.com"}
+	if !validProvider.IsValid() {
+		t.Error("provider should've been valid")
+	}
+}
+
+func TestAlertProvider_Send(t *testing.T) {
+	defer client.InjectHTTPClient(nil)
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name             string
+		Provider         AlertProvider
+		Alert            alert.Alert
+		Resolved         bool
+		MockRoundTripper test.MockRoundTripper
+		ExpectedError    bool
+	}{
+		{
+			Name:     "triggered",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "triggered-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+		{
+			Name:     "resolved",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "resolved-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			client.InjectHTTPClient(&http.Client{Transport: scenario.MockRoundTripper})
+			err := scenario.Provider.Send(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if scenario.ExpectedError && err == nil {
+				t.Error("expected error, got none")
+			}
+			if !scenario.ExpectedError && err != nil {
+				t.Error("expected no error, got", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_buildRequestBody(t *testing.T) {
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name         string
+		Provider     AlertProvider
+		Alert        alert.Alert
+		Resolved     bool
+		ExpectedBody string
+	}{
+		{
+			Name:         "triggered",
+			Provider:     AlertProvider{},
+			Alert:        alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     false,
+			ExpectedBody: "{\n  \"content\": \"\",\n  \"embeds\": [\n    {\n      \"title\": \":helmet_with_white_cross: Gatus\",\n      \"description\": \"An alert for **endpoint-name** has been triggered due to having failed 3 time(s) in a row:\\n> description-1\",\n      \"color\": 15158332,\n      \"fields\": [\n        {\n          \"name\": \"Condition results\",\n          \"value\": \":x: - `[CONNECTED] == true`\\n:x: - `[STATUS] == 200`\\n\",\n          \"inline\": false\n        }\n      ]\n    }\n  ]\n}",
+		},
+		{
+			Name:         "resolved",
+			Provider:     AlertProvider{},
+			Alert:        alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     true,
+			ExpectedBody: "{\n  \"content\": \"\",\n  \"embeds\": [\n    {\n      \"title\": \":helmet_with_white_cross: Gatus\",\n      \"description\": \"An alert for **endpoint-name** has been resolved after passing successfully 5 time(s) in a row:\\n> description-2\",\n      \"color\": 3066993,\n      \"fields\": [\n        {\n          \"name\": \"Condition results\",\n          \"value\": \":white_check_mark: - `[CONNECTED] == true`\\n:white_check_mark: - `[STATUS] == 200`\\n\",\n          \"inline\": false\n        }\n      ]\n    }\n  ]\n}",
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			body := scenario.Provider.buildRequestBody(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if body != scenario.ExpectedBody {
+				t.Errorf("expected %s, got %s", scenario.ExpectedBody, body)
+			}
+			out := make(map[string]interface{})
+			if err := json.Unmarshal([]byte(body), &out); err != nil {
+				t.Error("expected body to be valid JSON, got error:", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_GetDefaultAlert(t *testing.T) {
+	if (AlertProvider{DefaultAlert: &alert.Alert{}}).GetDefaultAlert() == nil {
+		t.Error("expected default alert to be not nil")
+	}
+	if (AlertProvider{DefaultAlert: nil}).GetDefaultAlert() != nil {
+		t.Error("expected default alert to be nil")
+	}
+}

alerting/provider/email/email.go

@@ -0,0 +1,71 @@
+package email
+
+import (
+	"fmt"
+	"math"
+	"strings"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/core"
+	gomail "gopkg.in/mail.v2"
+)
+
+// AlertProvider is the configuration necessary for sending an alert using SMTP
+type AlertProvider struct {
+	From     string `yaml:"from"`
+	Password string `yaml:"password"`
+	Host     string `yaml:"host"`
+	Port     int    `yaml:"port"`
+	To       string `yaml:"to"`
+
+	// DefaultAlert is the default alert configuration to use for endpoints with an alert of the appropriate type
+	DefaultAlert *alert.Alert `yaml:"default-alert,omitempty"`
+}
+
+// IsValid returns whether the provider's configuration is valid
+func (provider *AlertProvider) IsValid() bool {
+	return len(provider.From) > 0 && len(provider.Password) > 0 && len(provider.Host) > 0 && len(provider.To) > 0 && provider.Port > 0 && provider.Port < math.MaxUint16
+}
+
+// Send an alert using the provider
+func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) error {
+	subject, body := provider.buildMessageSubjectAndBody(endpoint, alert, result, resolved)
+	m := gomail.NewMessage()
+	m.SetHeader("From", provider.From)
+	m.SetHeader("To", strings.Split(provider.To, ",")...)
+	m.SetHeader("Subject", subject)
+	m.SetBody("text/plain", body)
+	d := gomail.NewDialer(provider.Host, provider.Port, provider.From, provider.Password)
+	return d.DialAndSend(m)
+}
+
+// buildMessageSubjectAndBody builds the message subject and body
+func (provider *AlertProvider) buildMessageSubjectAndBody(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) (string, string) {
+	var subject, message, results string
+	if resolved {
+		subject = fmt.Sprintf("[%s] Alert resolved", endpoint.Name)
+		message = fmt.Sprintf("An alert for %s has been resolved after passing successfully %d time(s) in a row", endpoint.Name, alert.SuccessThreshold)
+	} else {
+		subject = fmt.Sprintf("[%s] Alert triggered", endpoint.Name)
+		message = fmt.Sprintf("An alert for %s has been triggered due to having failed %d time(s) in a row", endpoint.Name, alert.FailureThreshold)
+	}
+	for _, conditionResult := range result.ConditionResults {
+		var prefix string
+		if conditionResult.Success {
+			prefix = "✅"
+		} else {
+			prefix = "❌"
+		}
+		results += fmt.Sprintf("%s %s\n", prefix, conditionResult.Condition)
+	}
+	var description string
+	if alertDescription := alert.GetDescription(); len(alertDescription) > 0 {
+		description = "\n\nAlert description: " + alertDescription
+	}
+	return subject, message + description + "\n\nCondition results:\n" + results
+}
+
+// GetDefaultAlert returns the provider's default alert configuration
+func (provider AlertProvider) GetDefaultAlert() *alert.Alert {
+	return provider.DefaultAlert
+}

alerting/provider/email/email_test.go

@@ -0,0 +1,79 @@
+package email
+
+import (
+	"testing"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/core"
+)
+
+func TestAlertProvider_IsValid(t *testing.T) {
+	invalidProvider := AlertProvider{}
+	if invalidProvider.IsValid() {
+		t.Error("provider shouldn't have been valid")
+	}
+	validProvider := AlertProvider{From: "from@example.com", Password: "password", Host: "smtp.gmail.com", Port: 587, To: "to@example.com"}
+	if !validProvider.IsValid() {
+		t.Error("provider should've been valid")
+	}
+}
+
+func TestAlertProvider_buildRequestBody(t *testing.T) {
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name            string
+		Provider        AlertProvider
+		Alert           alert.Alert
+		Resolved        bool
+		ExpectedSubject string
+		ExpectedBody    string
+	}{
+		{
+			Name:            "triggered",
+			Provider:        AlertProvider{},
+			Alert:           alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:        false,
+			ExpectedSubject: "[endpoint-name] Alert triggered",
+			ExpectedBody:    "An alert for endpoint-name has been triggered due to having failed 3 time(s) in a row\n\nAlert description: description-1\n\nCondition results:\n❌ [CONNECTED] == true\n❌ [STATUS] == 200\n",
+		},
+		{
+			Name:            "resolved",
+			Provider:        AlertProvider{},
+			Alert:           alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:        true,
+			ExpectedSubject: "[endpoint-name] Alert resolved",
+			ExpectedBody:    "An alert for endpoint-name has been resolved after passing successfully 5 time(s) in a row\n\nAlert description: description-2\n\nCondition results:\n✅ [CONNECTED] == true\n✅ [STATUS] == 200\n",
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			subject, body := scenario.Provider.buildMessageSubjectAndBody(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if subject != scenario.ExpectedSubject {
+				t.Errorf("expected subject to be %s, got %s", scenario.ExpectedSubject, subject)
+			}
+			if body != scenario.ExpectedBody {
+				t.Errorf("expected body to be %s, got %s", scenario.ExpectedBody, body)
+			}
+		})
+	}
+}
+
+func TestAlertProvider_GetDefaultAlert(t *testing.T) {
+	if (AlertProvider{DefaultAlert: &alert.Alert{}}).GetDefaultAlert() == nil {
+		t.Error("expected default alert to be not nil")
+	}
+	if (AlertProvider{DefaultAlert: nil}).GetDefaultAlert() != nil {
+		t.Error("expected default alert to be nil")
+	}
+}

alerting/provider/mattermost/mattermost.go

@@ -0,0 +1,107 @@
+package mattermost
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+)
+
+// AlertProvider is the configuration necessary for sending an alert using Mattermost
+type AlertProvider struct {
+	WebhookURL string `yaml:"webhook-url"`
+
+	// ClientConfig is the configuration of the client used to communicate with the provider's target
+	ClientConfig *client.Config `yaml:"client"`
+
+	// DefaultAlert is the default alert configuration to use for endpoints with an alert of the appropriate type
+	DefaultAlert *alert.Alert `yaml:"default-alert"`
+}
+
+// IsValid returns whether the provider's configuration is valid
+func (provider *AlertProvider) IsValid() bool {
+	if provider.ClientConfig == nil {
+		provider.ClientConfig = client.GetDefaultConfig()
+	}
+	return len(provider.WebhookURL) > 0
+}
+
+// Send an alert using the provider
+func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) error {
+	buffer := bytes.NewBuffer([]byte(provider.buildRequestBody(endpoint, alert, result, resolved)))
+	request, err := http.NewRequest(http.MethodPost, provider.WebhookURL, buffer)
+	if err != nil {
+		return err
+	}
+	request.Header.Set("Content-Type", "application/json")
+	response, err := client.GetHTTPClient(provider.ClientConfig).Do(request)
+	if err != nil {
+		return err
+	}
+	if response.StatusCode > 399 {
+		body, _ := ioutil.ReadAll(response.Body)
+		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
+	}
+	return err
+}
+
+// buildRequestBody builds the request body for the provider
+func (provider *AlertProvider) buildRequestBody(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) string {
+	var message, color string
+	if resolved {
+		message = fmt.Sprintf("An alert for *%s* has been resolved after passing successfully %d time(s) in a row", endpoint.Name, alert.SuccessThreshold)
+		color = "#36A64F"
+	} else {
+		message = fmt.Sprintf("An alert for *%s* has been triggered due to having failed %d time(s) in a row", endpoint.Name, alert.FailureThreshold)
+		color = "#DD0000"
+	}
+	var results string
+	for _, conditionResult := range result.ConditionResults {
+		var prefix string
+		if conditionResult.Success {
+			prefix = ":white_check_mark:"
+		} else {
+			prefix = ":x:"
+		}
+		results += fmt.Sprintf("%s - `%s`\\n", prefix, conditionResult.Condition)
+	}
+	var description string
+	if alertDescription := alert.GetDescription(); len(alertDescription) > 0 {
+		description = ":\\n> " + alertDescription
+	}
+	return fmt.Sprintf(`{
+  "text": "",
+  "username": "gatus",
+  "icon_url": "https://raw.githubusercontent.com/TwiN/gatus/master/.github/assets/logo.png",
+  "attachments": [
+    {
+      "title": ":rescue_worker_helmet: Gatus",
+      "fallback": "Gatus - %s",
+      "text": "%s%s",
+      "short": false,
+      "color": "%s",
+      "fields": [
+        {
+          "title": "URL",
+          "value": "%s",
+          "short": false
+        },
+        {
+          "title": "Condition results",
+          "value": "%s",
+          "short": false
+        }
+      ]
+    }
+  ]
+}`, message, message, description, color, endpoint.URL, results)
+}
+
+// GetDefaultAlert returns the provider's default alert configuration
+func (provider AlertProvider) GetDefaultAlert() *alert.Alert {
+	return provider.DefaultAlert
+}

alerting/provider/mattermost/mattermost_test.go

@@ -0,0 +1,158 @@
+package mattermost
+
+import (
+	"encoding/json"
+	"net/http"
+	"testing"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+	"github.com/TwiN/gatus/v3/test"
+)
+
+func TestAlertProvider_IsValid(t *testing.T) {
+	invalidProvider := AlertProvider{WebhookURL: ""}
+	if invalidProvider.IsValid() {
+		t.Error("provider shouldn't have been valid")
+	}
+	validProvider := AlertProvider{WebhookURL: "http://example.com"}
+	if !validProvider.IsValid() {
+		t.Error("provider should've been valid")
+	}
+}
+
+func TestAlertProvider_Send(t *testing.T) {
+	defer client.InjectHTTPClient(nil)
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name             string
+		Provider         AlertProvider
+		Alert            alert.Alert
+		Resolved         bool
+		MockRoundTripper test.MockRoundTripper
+		ExpectedError    bool
+	}{
+		{
+			Name:     "triggered",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "triggered-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+		{
+			Name:     "resolved",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "resolved-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			client.InjectHTTPClient(&http.Client{Transport: scenario.MockRoundTripper})
+			err := scenario.Provider.Send(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if scenario.ExpectedError && err == nil {
+				t.Error("expected error, got none")
+			}
+			if !scenario.ExpectedError && err != nil {
+				t.Error("expected no error, got", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_buildRequestBody(t *testing.T) {
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name         string
+		Provider     AlertProvider
+		Alert        alert.Alert
+		Resolved     bool
+		ExpectedBody string
+	}{
+		{
+			Name:         "triggered",
+			Provider:     AlertProvider{},
+			Alert:        alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     false,
+			ExpectedBody: "{\n  \"text\": \"\",\n  \"username\": \"gatus\",\n  \"icon_url\": \"https://raw.githubusercontent.com/TwiN/gatus/master/.github/assets/logo.png\",\n  \"attachments\": [\n    {\n      \"title\": \":rescue_worker_helmet: Gatus\",\n      \"fallback\": \"Gatus - An alert for *endpoint-name* has been triggered due to having failed 3 time(s) in a row\",\n      \"text\": \"An alert for *endpoint-name* has been triggered due to having failed 3 time(s) in a row:\\n> description-1\",\n      \"short\": false,\n      \"color\": \"#DD0000\",\n      \"fields\": [\n        {\n          \"title\": \"URL\",\n          \"value\": \"\",\n          \"short\": false\n        },\n        {\n          \"title\": \"Condition results\",\n          \"value\": \":x: - `[CONNECTED] == true`\\n:x: - `[STATUS] == 200`\\n\",\n          \"short\": false\n        }\n      ]\n    }\n  ]\n}",
+		},
+		{
+			Name:         "resolved",
+			Provider:     AlertProvider{},
+			Alert:        alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     true,
+			ExpectedBody: "{\n  \"text\": \"\",\n  \"username\": \"gatus\",\n  \"icon_url\": \"https://raw.githubusercontent.com/TwiN/gatus/master/.github/assets/logo.png\",\n  \"attachments\": [\n    {\n      \"title\": \":rescue_worker_helmet: Gatus\",\n      \"fallback\": \"Gatus - An alert for *endpoint-name* has been resolved after passing successfully 5 time(s) in a row\",\n      \"text\": \"An alert for *endpoint-name* has been resolved after passing successfully 5 time(s) in a row:\\n> description-2\",\n      \"short\": false,\n      \"color\": \"#36A64F\",\n      \"fields\": [\n        {\n          \"title\": \"URL\",\n          \"value\": \"\",\n          \"short\": false\n        },\n        {\n          \"title\": \"Condition results\",\n          \"value\": \":white_check_mark: - `[CONNECTED] == true`\\n:white_check_mark: - `[STATUS] == 200`\\n\",\n          \"short\": false\n        }\n      ]\n    }\n  ]\n}",
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			body := scenario.Provider.buildRequestBody(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if body != scenario.ExpectedBody {
+				t.Errorf("expected %s, got %s", scenario.ExpectedBody, body)
+			}
+			out := make(map[string]interface{})
+			if err := json.Unmarshal([]byte(body), &out); err != nil {
+				t.Error("expected body to be valid JSON, got error:", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_GetDefaultAlert(t *testing.T) {
+	if (AlertProvider{DefaultAlert: &alert.Alert{}}).GetDefaultAlert() == nil {
+		t.Error("expected default alert to be not nil")
+	}
+	if (AlertProvider{DefaultAlert: nil}).GetDefaultAlert() != nil {
+		t.Error("expected default alert to be nil")
+	}
+}

alerting/provider/messagebird/messagebird.go

@@ -0,0 +1,72 @@
+package messagebird
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+)
+
+const (
+	restAPIURL = "https://rest.messagebird.com/messages"
+)
+
+// AlertProvider is the configuration necessary for sending an alert using Messagebird
+type AlertProvider struct {
+	AccessKey  string `yaml:"access-key"`
+	Originator string `yaml:"originator"`
+	Recipients string `yaml:"recipients"`
+
+	// DefaultAlert is the default alert configuration to use for endpoints with an alert of the appropriate type
+	DefaultAlert *alert.Alert `yaml:"default-alert,omitempty"`
+}
+
+// IsValid returns whether the provider's configuration is valid
+func (provider *AlertProvider) IsValid() bool {
+	return len(provider.AccessKey) > 0 && len(provider.Originator) > 0 && len(provider.Recipients) > 0
+}
+
+// Send an alert using the provider
+// Reference doc for messagebird: https://developers.messagebird.com/api/sms-messaging/#send-outbound-sms
+func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) error {
+	buffer := bytes.NewBuffer([]byte(provider.buildRequestBody(endpoint, alert, result, resolved)))
+	request, err := http.NewRequest(http.MethodPost, restAPIURL, buffer)
+	if err != nil {
+		return err
+	}
+	request.Header.Set("Content-Type", "application/json")
+	request.Header.Set("Authorization", fmt.Sprintf("AccessKey %s", provider.AccessKey))
+	response, err := client.GetHTTPClient(nil).Do(request)
+	if err != nil {
+		return err
+	}
+	if response.StatusCode > 399 {
+		body, _ := ioutil.ReadAll(response.Body)
+		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
+	}
+	return err
+}
+
+// buildRequestBody builds the request body for the provider
+func (provider *AlertProvider) buildRequestBody(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) string {
+	var message string
+	if resolved {
+		message = fmt.Sprintf("RESOLVED: %s - %s", endpoint.Name, alert.GetDescription())
+	} else {
+		message = fmt.Sprintf("TRIGGERED: %s - %s", endpoint.Name, alert.GetDescription())
+	}
+	return fmt.Sprintf(`{
+  "originator": "%s",
+  "recipients": "%s",
+  "body": "%s"
+}`, provider.Originator, provider.Recipients, message)
+}
+
+// GetDefaultAlert returns the provider's default alert configuration
+func (provider AlertProvider) GetDefaultAlert() *alert.Alert {
+	return provider.DefaultAlert
+}

alerting/provider/messagebird/messagebird_test.go

@@ -0,0 +1,162 @@
+package messagebird
+
+import (
+	"encoding/json"
+	"net/http"
+	"testing"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+	"github.com/TwiN/gatus/v3/test"
+)
+
+func TestMessagebirdAlertProvider_IsValid(t *testing.T) {
+	invalidProvider := AlertProvider{}
+	if invalidProvider.IsValid() {
+		t.Error("provider shouldn't have been valid")
+	}
+	validProvider := AlertProvider{
+		AccessKey:  "1",
+		Originator: "1",
+		Recipients: "1",
+	}
+	if !validProvider.IsValid() {
+		t.Error("provider should've been valid")
+	}
+}
+
+func TestAlertProvider_Send(t *testing.T) {
+	defer client.InjectHTTPClient(nil)
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name             string
+		Provider         AlertProvider
+		Alert            alert.Alert
+		Resolved         bool
+		MockRoundTripper test.MockRoundTripper
+		ExpectedError    bool
+	}{
+		{
+			Name:     "triggered",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "triggered-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+		{
+			Name:     "resolved",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "resolved-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			client.InjectHTTPClient(&http.Client{Transport: scenario.MockRoundTripper})
+			err := scenario.Provider.Send(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if scenario.ExpectedError && err == nil {
+				t.Error("expected error, got none")
+			}
+			if !scenario.ExpectedError && err != nil {
+				t.Error("expected no error, got", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_buildRequestBody(t *testing.T) {
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name         string
+		Provider     AlertProvider
+		Alert        alert.Alert
+		Resolved     bool
+		ExpectedBody string
+	}{
+		{
+			Name:         "triggered",
+			Provider:     AlertProvider{AccessKey: "1", Originator: "2", Recipients: "3"},
+			Alert:        alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     false,
+			ExpectedBody: "{\n  \"originator\": \"2\",\n  \"recipients\": \"3\",\n  \"body\": \"TRIGGERED: endpoint-name - description-1\"\n}",
+		},
+		{
+			Name:         "resolved",
+			Provider:     AlertProvider{AccessKey: "4", Originator: "5", Recipients: "6"},
+			Alert:        alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     true,
+			ExpectedBody: "{\n  \"originator\": \"5\",\n  \"recipients\": \"6\",\n  \"body\": \"RESOLVED: endpoint-name - description-2\"\n}",
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			body := scenario.Provider.buildRequestBody(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if body != scenario.ExpectedBody {
+				t.Errorf("expected %s, got %s", scenario.ExpectedBody, body)
+			}
+			out := make(map[string]interface{})
+			if err := json.Unmarshal([]byte(body), &out); err != nil {
+				t.Error("expected body to be valid JSON, got error:", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_GetDefaultAlert(t *testing.T) {
+	if (AlertProvider{DefaultAlert: &alert.Alert{}}).GetDefaultAlert() == nil {
+		t.Error("expected default alert to be not nil")
+	}
+	if (AlertProvider{DefaultAlert: nil}).GetDefaultAlert() != nil {
+		t.Error("expected default alert to be nil")
+	}
+}

alerting/provider/pagerduty/pagerduty.go

@@ -0,0 +1,134 @@
+package pagerduty
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+)
+
+const (
+	restAPIURL = "https://events.pagerduty.com/v2/enqueue"
+)
+
+// AlertProvider is the configuration necessary for sending an alert using PagerDuty
+type AlertProvider struct {
+	IntegrationKey string `yaml:"integration-key"`
+
+	// DefaultAlert is the default alert configuration to use for endpoints with an alert of the appropriate type
+	DefaultAlert *alert.Alert `yaml:"default-alert,omitempty"`
+
+	// Overrides is a list of Override that may be prioritized over the default configuration
+	Overrides []Override `yaml:"overrides,omitempty"`
+}
+
+// Override is a case under which the default integration is overridden
+type Override struct {
+	Group          string `yaml:"group"`
+	IntegrationKey string `yaml:"integration-key"`
+}
+
+// IsValid returns whether the provider's configuration is valid
+func (provider *AlertProvider) IsValid() bool {
+	registeredGroups := make(map[string]bool)
+	if provider.Overrides != nil {
+		for _, override := range provider.Overrides {
+			if isAlreadyRegistered := registeredGroups[override.Group]; isAlreadyRegistered || override.Group == "" || len(override.IntegrationKey) != 32 {
+				return false
+			}
+			registeredGroups[override.Group] = true
+		}
+	}
+	// Either the default integration key has the right length, or there are overrides who are properly configured.
+	return len(provider.IntegrationKey) == 32 || len(provider.Overrides) != 0
+}
+
+// Send an alert using the provider
+//
+// Relevant: https://developer.pagerduty.com/docs/events-api-v2/trigger-events/
+func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) error {
+	buffer := bytes.NewBuffer([]byte(provider.buildRequestBody(endpoint, alert, result, resolved)))
+	request, err := http.NewRequest(http.MethodPost, restAPIURL, buffer)
+	if err != nil {
+		return err
+	}
+	request.Header.Set("Content-Type", "application/json")
+	response, err := client.GetHTTPClient(nil).Do(request)
+	if err != nil {
+		return err
+	}
+	if response.StatusCode > 399 {
+		body, _ := ioutil.ReadAll(response.Body)
+		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
+	}
+	if alert.IsSendingOnResolved() {
+		if resolved {
+			// The alert has been resolved and there's no error, so we can clear the alert's ResolveKey
+			alert.ResolveKey = ""
+		} else {
+			// We need to retrieve the resolve key from the response
+			body, err := ioutil.ReadAll(response.Body)
+			var payload pagerDutyResponsePayload
+			if err = json.Unmarshal(body, &payload); err != nil {
+				// Silently fail. We don't want to create tons of alerts just because we failed to parse the body.
+				log.Printf("[pagerduty][Send] Ran into error unmarshaling pagerduty response: %s", err.Error())
+			} else {
+				alert.ResolveKey = payload.DedupKey
+			}
+		}
+	}
+	return nil
+}
+
+// buildRequestBody builds the request body for the provider
+func (provider *AlertProvider) buildRequestBody(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) string {
+	var message, eventAction, resolveKey string
+	if resolved {
+		message = fmt.Sprintf("RESOLVED: %s - %s", endpoint.Name, alert.GetDescription())
+		eventAction = "resolve"
+		resolveKey = alert.ResolveKey
+	} else {
+		message = fmt.Sprintf("TRIGGERED: %s - %s", endpoint.Name, alert.GetDescription())
+		eventAction = "trigger"
+		resolveKey = ""
+	}
+	return fmt.Sprintf(`{
+  "routing_key": "%s",
+  "dedup_key": "%s",
+  "event_action": "%s",
+  "payload": {
+    "summary": "%s",
+    "source": "%s",
+    "severity": "critical"
+  }
+}`, provider.getIntegrationKeyForGroup(endpoint.Group), resolveKey, eventAction, message, endpoint.Name)
+}
+
+// getIntegrationKeyForGroup returns the appropriate pagerduty integration key for a given group
+func (provider *AlertProvider) getIntegrationKeyForGroup(group string) string {
+	if provider.Overrides != nil {
+		for _, override := range provider.Overrides {
+			if group == override.Group {
+				return override.IntegrationKey
+			}
+		}
+	}
+	return provider.IntegrationKey
+}
+
+// GetDefaultAlert returns the provider's default alert configuration
+func (provider AlertProvider) GetDefaultAlert() *alert.Alert {
+	return provider.DefaultAlert
+}
+
+type pagerDutyResponsePayload struct {
+	Status   string `json:"status"`
+	Message  string `json:"message"`
+	DedupKey string `json:"dedup_key"`
+}

alerting/provider/pagerduty/pagerduty_test.go

@@ -0,0 +1,246 @@
+package pagerduty
+
+import (
+	"encoding/json"
+	"net/http"
+	"testing"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+	"github.com/TwiN/gatus/v3/test"
+)
+
+func TestAlertProvider_IsValid(t *testing.T) {
+	invalidProvider := AlertProvider{IntegrationKey: ""}
+	if invalidProvider.IsValid() {
+		t.Error("provider shouldn't have been valid")
+	}
+	validProvider := AlertProvider{IntegrationKey: "00000000000000000000000000000000"}
+	if !validProvider.IsValid() {
+		t.Error("provider should've been valid")
+	}
+}
+
+func TestAlertProvider_IsValidWithOverride(t *testing.T) {
+	providerWithInvalidOverrideGroup := AlertProvider{
+		Overrides: []Override{
+			{
+				IntegrationKey: "00000000000000000000000000000000",
+				Group:          "",
+			},
+		},
+	}
+	if providerWithInvalidOverrideGroup.IsValid() {
+		t.Error("provider Group shouldn't have been valid")
+	}
+	providerWithInvalidOverrideIntegrationKey := AlertProvider{
+		Overrides: []Override{
+			{
+				IntegrationKey: "",
+				Group:          "group",
+			},
+		},
+	}
+	if providerWithInvalidOverrideIntegrationKey.IsValid() {
+		t.Error("provider integration key shouldn't have been valid")
+	}
+	providerWithValidOverride := AlertProvider{
+		Overrides: []Override{
+			{
+				IntegrationKey: "00000000000000000000000000000000",
+				Group:          "group",
+			},
+		},
+	}
+	if !providerWithValidOverride.IsValid() {
+		t.Error("provider should've been valid")
+	}
+}
+
+func TestAlertProvider_Send(t *testing.T) {
+	defer client.InjectHTTPClient(nil)
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name             string
+		Provider         AlertProvider
+		Alert            alert.Alert
+		Resolved         bool
+		MockRoundTripper test.MockRoundTripper
+		ExpectedError    bool
+	}{
+		{
+			Name:     "triggered",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "triggered-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+		{
+			Name:     "resolved",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "resolved-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			client.InjectHTTPClient(&http.Client{Transport: scenario.MockRoundTripper})
+			err := scenario.Provider.Send(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if scenario.ExpectedError && err == nil {
+				t.Error("expected error, got none")
+			}
+			if !scenario.ExpectedError && err != nil {
+				t.Error("expected no error, got", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_buildRequestBody(t *testing.T) {
+	description := "test"
+	scenarios := []struct {
+		Name         string
+		Provider     AlertProvider
+		Alert        alert.Alert
+		Resolved     bool
+		ExpectedBody string
+	}{
+		{
+			Name:         "triggered",
+			Provider:     AlertProvider{IntegrationKey: "00000000000000000000000000000000"},
+			Alert:        alert.Alert{Description: &description},
+			Resolved:     false,
+			ExpectedBody: "{\n  \"routing_key\": \"00000000000000000000000000000000\",\n  \"dedup_key\": \"\",\n  \"event_action\": \"trigger\",\n  \"payload\": {\n    \"summary\": \"TRIGGERED:  - test\",\n    \"source\": \"\",\n    \"severity\": \"critical\"\n  }\n}",
+		},
+		{
+			Name:         "resolved",
+			Provider:     AlertProvider{IntegrationKey: "00000000000000000000000000000000"},
+			Alert:        alert.Alert{Description: &description, ResolveKey: "key"},
+			Resolved:     true,
+			ExpectedBody: "{\n  \"routing_key\": \"00000000000000000000000000000000\",\n  \"dedup_key\": \"key\",\n  \"event_action\": \"resolve\",\n  \"payload\": {\n    \"summary\": \"RESOLVED:  - test\",\n    \"source\": \"\",\n    \"severity\": \"critical\"\n  }\n}",
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			body := scenario.Provider.buildRequestBody(&core.Endpoint{}, &scenario.Alert, &core.Result{}, scenario.Resolved)
+			if body != scenario.ExpectedBody {
+				t.Errorf("expected %s, got %s", scenario.ExpectedBody, body)
+			}
+			out := make(map[string]interface{})
+			if err := json.Unmarshal([]byte(body), &out); err != nil {
+				t.Error("expected body to be valid JSON, got error:", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_getIntegrationKeyForGroup(t *testing.T) {
+	scenarios := []struct {
+		Name           string
+		Provider       AlertProvider
+		InputGroup     string
+		ExpectedOutput string
+	}{
+		{
+			Name: "provider-no-override-specify-no-group-should-default",
+			Provider: AlertProvider{
+				IntegrationKey: "00000000000000000000000000000001",
+				Overrides:      nil,
+			},
+			InputGroup:     "",
+			ExpectedOutput: "00000000000000000000000000000001",
+		},
+		{
+			Name: "provider-no-override-specify-group-should-default",
+			Provider: AlertProvider{
+				IntegrationKey: "00000000000000000000000000000001",
+				Overrides:      nil,
+			},
+			InputGroup:     "group",
+			ExpectedOutput: "00000000000000000000000000000001",
+		},
+		{
+			Name: "provider-with-override-specify-no-group-should-default",
+			Provider: AlertProvider{
+				IntegrationKey: "00000000000000000000000000000001",
+				Overrides: []Override{
+					{
+						Group:          "group",
+						IntegrationKey: "00000000000000000000000000000002",
+					},
+				},
+			},
+			InputGroup:     "",
+			ExpectedOutput: "00000000000000000000000000000001",
+		},
+		{
+			Name: "provider-with-override-specify-group-should-override",
+			Provider: AlertProvider{
+				IntegrationKey: "00000000000000000000000000000001",
+				Overrides: []Override{
+					{
+						Group:          "group",
+						IntegrationKey: "00000000000000000000000000000002",
+					},
+				},
+			},
+			InputGroup:     "group",
+			ExpectedOutput: "00000000000000000000000000000002",
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			if output := scenario.Provider.getIntegrationKeyForGroup(scenario.InputGroup); output != scenario.ExpectedOutput {
+				t.Errorf("expected %s, got %s", scenario.ExpectedOutput, output)
+			}
+		})
+	}
+}
+
+func TestAlertProvider_GetDefaultAlert(t *testing.T) {
+	if (AlertProvider{DefaultAlert: &alert.Alert{}}).GetDefaultAlert() == nil {
+		t.Error("expected default alert to be not nil")
+	}
+	if (AlertProvider{DefaultAlert: nil}).GetDefaultAlert() != nil {
+		t.Error("expected default alert to be nil")
+	}
+}

alerting/provider/provider.go

@@ -0,0 +1,64 @@
+package provider
+
+import (
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/alerting/provider/custom"
+	"github.com/TwiN/gatus/v3/alerting/provider/discord"
+	"github.com/TwiN/gatus/v3/alerting/provider/email"
+	"github.com/TwiN/gatus/v3/alerting/provider/mattermost"
+	"github.com/TwiN/gatus/v3/alerting/provider/messagebird"
+	"github.com/TwiN/gatus/v3/alerting/provider/pagerduty"
+	"github.com/TwiN/gatus/v3/alerting/provider/slack"
+	"github.com/TwiN/gatus/v3/alerting/provider/teams"
+	"github.com/TwiN/gatus/v3/alerting/provider/telegram"
+	"github.com/TwiN/gatus/v3/alerting/provider/twilio"
+	"github.com/TwiN/gatus/v3/core"
+)
+
+// AlertProvider is the interface that each providers should implement
+type AlertProvider interface {
+	// IsValid returns whether the provider's configuration is valid
+	IsValid() bool
+
+	// GetDefaultAlert returns the provider's default alert configuration
+	GetDefaultAlert() *alert.Alert
+
+	// Send an alert using the provider
+	Send(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) error
+}
+
+// ParseWithDefaultAlert parses an Endpoint alert by using the provider's default alert as a baseline
+func ParseWithDefaultAlert(providerDefaultAlert, endpointAlert *alert.Alert) {
+	if providerDefaultAlert == nil || endpointAlert == nil {
+		return
+	}
+	if endpointAlert.Enabled == nil {
+		endpointAlert.Enabled = providerDefaultAlert.Enabled
+	}
+	if endpointAlert.SendOnResolved == nil {
+		endpointAlert.SendOnResolved = providerDefaultAlert.SendOnResolved
+	}
+	if endpointAlert.Description == nil {
+		endpointAlert.Description = providerDefaultAlert.Description
+	}
+	if endpointAlert.FailureThreshold == 0 {
+		endpointAlert.FailureThreshold = providerDefaultAlert.FailureThreshold
+	}
+	if endpointAlert.SuccessThreshold == 0 {
+		endpointAlert.SuccessThreshold = providerDefaultAlert.SuccessThreshold
+	}
+}
+
+var (
+	// Validate interface implementation on compile
+	_ AlertProvider = (*custom.AlertProvider)(nil)
+	_ AlertProvider = (*discord.AlertProvider)(nil)
+	_ AlertProvider = (*email.AlertProvider)(nil)
+	_ AlertProvider = (*mattermost.AlertProvider)(nil)
+	_ AlertProvider = (*messagebird.AlertProvider)(nil)
+	_ AlertProvider = (*pagerduty.AlertProvider)(nil)
+	_ AlertProvider = (*slack.AlertProvider)(nil)
+	_ AlertProvider = (*teams.AlertProvider)(nil)
+	_ AlertProvider = (*telegram.AlertProvider)(nil)
+	_ AlertProvider = (*twilio.AlertProvider)(nil)
+)

alerting/provider/provider_test.go

@@ -0,0 +1,153 @@
+package provider
+
+import (
+	"testing"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+)
+
+func TestParseWithDefaultAlert(t *testing.T) {
+	type Scenario struct {
+		Name                                             string
+		DefaultAlert, EndpointAlert, ExpectedOutputAlert *alert.Alert
+	}
+	enabled := true
+	disabled := false
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []Scenario{
+		{
+			Name: "endpoint-alert-type-only",
+			DefaultAlert: &alert.Alert{
+				Enabled:          &enabled,
+				SendOnResolved:   &enabled,
+				Description:      &firstDescription,
+				FailureThreshold: 5,
+				SuccessThreshold: 10,
+			},
+			EndpointAlert: &alert.Alert{
+				Type: alert.TypeDiscord,
+			},
+			ExpectedOutputAlert: &alert.Alert{
+				Type:             alert.TypeDiscord,
+				Enabled:          &enabled,
+				SendOnResolved:   &enabled,
+				Description:      &firstDescription,
+				FailureThreshold: 5,
+				SuccessThreshold: 10,
+			},
+		},
+		{
+			Name: "endpoint-alert-overwrites-default-alert",
+			DefaultAlert: &alert.Alert{
+				Enabled:          &disabled,
+				SendOnResolved:   &disabled,
+				Description:      &firstDescription,
+				FailureThreshold: 5,
+				SuccessThreshold: 10,
+			},
+			EndpointAlert: &alert.Alert{
+				Type:             alert.TypeTelegram,
+				Enabled:          &enabled,
+				SendOnResolved:   &enabled,
+				Description:      &secondDescription,
+				FailureThreshold: 6,
+				SuccessThreshold: 11,
+			},
+			ExpectedOutputAlert: &alert.Alert{
+				Type:             alert.TypeTelegram,
+				Enabled:          &enabled,
+				SendOnResolved:   &enabled,
+				Description:      &secondDescription,
+				FailureThreshold: 6,
+				SuccessThreshold: 11,
+			},
+		},
+		{
+			Name: "endpoint-alert-partially-overwrites-default-alert",
+			DefaultAlert: &alert.Alert{
+				Enabled:          &enabled,
+				SendOnResolved:   &enabled,
+				Description:      &firstDescription,
+				FailureThreshold: 5,
+				SuccessThreshold: 10,
+			},
+			EndpointAlert: &alert.Alert{
+				Type:             alert.TypeDiscord,
+				Enabled:          nil,
+				SendOnResolved:   nil,
+				FailureThreshold: 6,
+				SuccessThreshold: 11,
+			},
+			ExpectedOutputAlert: &alert.Alert{
+				Type:             alert.TypeDiscord,
+				Enabled:          &enabled,
+				SendOnResolved:   &enabled,
+				Description:      &firstDescription,
+				FailureThreshold: 6,
+				SuccessThreshold: 11,
+			},
+		},
+		{
+			Name: "default-alert-type-should-be-ignored",
+			DefaultAlert: &alert.Alert{
+				Type:             alert.TypeTelegram,
+				Enabled:          &enabled,
+				SendOnResolved:   &enabled,
+				Description:      &firstDescription,
+				FailureThreshold: 5,
+				SuccessThreshold: 10,
+			},
+			EndpointAlert: &alert.Alert{
+				Type: alert.TypeDiscord,
+			},
+			ExpectedOutputAlert: &alert.Alert{
+				Type:             alert.TypeDiscord,
+				Enabled:          &enabled,
+				SendOnResolved:   &enabled,
+				Description:      &firstDescription,
+				FailureThreshold: 5,
+				SuccessThreshold: 10,
+			},
+		},
+		{
+			Name: "no-default-alert",
+			DefaultAlert: &alert.Alert{
+				Type:             alert.TypeDiscord,
+				Enabled:          nil,
+				SendOnResolved:   nil,
+				Description:      &firstDescription,
+				FailureThreshold: 2,
+				SuccessThreshold: 5,
+			},
+			EndpointAlert:       nil,
+			ExpectedOutputAlert: nil,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			ParseWithDefaultAlert(scenario.DefaultAlert, scenario.EndpointAlert)
+			if scenario.ExpectedOutputAlert == nil {
+				if scenario.EndpointAlert != nil {
+					t.Fail()
+				}
+				return
+			}
+			if scenario.EndpointAlert.IsEnabled() != scenario.ExpectedOutputAlert.IsEnabled() {
+				t.Errorf("expected EndpointAlert.IsEnabled() to be %v, got %v", scenario.ExpectedOutputAlert.IsEnabled(), scenario.EndpointAlert.IsEnabled())
+			}
+			if scenario.EndpointAlert.IsSendingOnResolved() != scenario.ExpectedOutputAlert.IsSendingOnResolved() {
+				t.Errorf("expected EndpointAlert.IsSendingOnResolved() to be %v, got %v", scenario.ExpectedOutputAlert.IsSendingOnResolved(), scenario.EndpointAlert.IsSendingOnResolved())
+			}
+			if scenario.EndpointAlert.GetDescription() != scenario.ExpectedOutputAlert.GetDescription() {
+				t.Errorf("expected EndpointAlert.GetDescription() to be %v, got %v", scenario.ExpectedOutputAlert.GetDescription(), scenario.EndpointAlert.GetDescription())
+			}
+			if scenario.EndpointAlert.FailureThreshold != scenario.ExpectedOutputAlert.FailureThreshold {
+				t.Errorf("expected EndpointAlert.FailureThreshold to be %v, got %v", scenario.ExpectedOutputAlert.FailureThreshold, scenario.EndpointAlert.FailureThreshold)
+			}
+			if scenario.EndpointAlert.SuccessThreshold != scenario.ExpectedOutputAlert.SuccessThreshold {
+				t.Errorf("expected EndpointAlert.SuccessThreshold to be %v, got %v", scenario.ExpectedOutputAlert.SuccessThreshold, scenario.EndpointAlert.SuccessThreshold)
+			}
+		})
+	}
+}

alerting/provider/slack/slack.go

@@ -0,0 +1,92 @@
+package slack
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+)
+
+// AlertProvider is the configuration necessary for sending an alert using Slack
+type AlertProvider struct {
+	WebhookURL string `yaml:"webhook-url"` // Slack webhook URL
+
+	// DefaultAlert is the default alert configuration to use for endpoints with an alert of the appropriate type
+	DefaultAlert *alert.Alert `yaml:"default-alert"`
+}
+
+// IsValid returns whether the provider's configuration is valid
+func (provider *AlertProvider) IsValid() bool {
+	return len(provider.WebhookURL) > 0
+}
+
+// Send an alert using the provider
+func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) error {
+	buffer := bytes.NewBuffer([]byte(provider.buildRequestBody(endpoint, alert, result, resolved)))
+	request, err := http.NewRequest(http.MethodPost, provider.WebhookURL, buffer)
+	if err != nil {
+		return err
+	}
+	request.Header.Set("Content-Type", "application/json")
+	response, err := client.GetHTTPClient(nil).Do(request)
+	if err != nil {
+		return err
+	}
+	if response.StatusCode > 399 {
+		body, _ := ioutil.ReadAll(response.Body)
+		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
+	}
+	return err
+}
+
+// buildRequestBody builds the request body for the provider
+func (provider *AlertProvider) buildRequestBody(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) string {
+	var message, color, results string
+	if resolved {
+		message = fmt.Sprintf("An alert for *%s* has been resolved after passing successfully %d time(s) in a row", endpoint.Name, alert.SuccessThreshold)
+		color = "#36A64F"
+	} else {
+		message = fmt.Sprintf("An alert for *%s* has been triggered due to having failed %d time(s) in a row", endpoint.Name, alert.FailureThreshold)
+		color = "#DD0000"
+	}
+	for _, conditionResult := range result.ConditionResults {
+		var prefix string
+		if conditionResult.Success {
+			prefix = ":white_check_mark:"
+		} else {
+			prefix = ":x:"
+		}
+		results += fmt.Sprintf("%s - `%s`\\n", prefix, conditionResult.Condition)
+	}
+	var description string
+	if alertDescription := alert.GetDescription(); len(alertDescription) > 0 {
+		description = ":\\n> " + alertDescription
+	}
+	return fmt.Sprintf(`{
+  "text": "",
+  "attachments": [
+    {
+      "title": ":helmet_with_white_cross: Gatus",
+      "text": "%s%s",
+      "short": false,
+      "color": "%s",
+      "fields": [
+        {
+          "title": "Condition results",
+          "value": "%s",
+          "short": false
+        }
+      ]
+    }
+  ]
+}`, message, description, color, results)
+}
+
+// GetDefaultAlert returns the provider's default alert configuration
+func (provider AlertProvider) GetDefaultAlert() *alert.Alert {
+	return provider.DefaultAlert
+}

alerting/provider/slack/slack_test.go

@@ -0,0 +1,158 @@
+package slack
+
+import (
+	"encoding/json"
+	"net/http"
+	"testing"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+	"github.com/TwiN/gatus/v3/test"
+)
+
+func TestAlertProvider_IsValid(t *testing.T) {
+	invalidProvider := AlertProvider{WebhookURL: ""}
+	if invalidProvider.IsValid() {
+		t.Error("provider shouldn't have been valid")
+	}
+	validProvider := AlertProvider{WebhookURL: "http://example.com"}
+	if !validProvider.IsValid() {
+		t.Error("provider should've been valid")
+	}
+}
+
+func TestAlertProvider_Send(t *testing.T) {
+	defer client.InjectHTTPClient(nil)
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name             string
+		Provider         AlertProvider
+		Alert            alert.Alert
+		Resolved         bool
+		MockRoundTripper test.MockRoundTripper
+		ExpectedError    bool
+	}{
+		{
+			Name:     "triggered",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "triggered-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+		{
+			Name:     "resolved",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "resolved-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			client.InjectHTTPClient(&http.Client{Transport: scenario.MockRoundTripper})
+			err := scenario.Provider.Send(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if scenario.ExpectedError && err == nil {
+				t.Error("expected error, got none")
+			}
+			if !scenario.ExpectedError && err != nil {
+				t.Error("expected no error, got", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_buildRequestBody(t *testing.T) {
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name         string
+		Provider     AlertProvider
+		Alert        alert.Alert
+		Resolved     bool
+		ExpectedBody string
+	}{
+		{
+			Name:         "triggered",
+			Provider:     AlertProvider{},
+			Alert:        alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     false,
+			ExpectedBody: "{\n  \"text\": \"\",\n  \"attachments\": [\n    {\n      \"title\": \":helmet_with_white_cross: Gatus\",\n      \"text\": \"An alert for *endpoint-name* has been triggered due to having failed 3 time(s) in a row:\\n> description-1\",\n      \"short\": false,\n      \"color\": \"#DD0000\",\n      \"fields\": [\n        {\n          \"title\": \"Condition results\",\n          \"value\": \":x: - `[CONNECTED] == true`\\n:x: - `[STATUS] == 200`\\n\",\n          \"short\": false\n        }\n      ]\n    }\n  ]\n}",
+		},
+		{
+			Name:         "resolved",
+			Provider:     AlertProvider{},
+			Alert:        alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     true,
+			ExpectedBody: "{\n  \"text\": \"\",\n  \"attachments\": [\n    {\n      \"title\": \":helmet_with_white_cross: Gatus\",\n      \"text\": \"An alert for *endpoint-name* has been resolved after passing successfully 5 time(s) in a row:\\n> description-2\",\n      \"short\": false,\n      \"color\": \"#36A64F\",\n      \"fields\": [\n        {\n          \"title\": \"Condition results\",\n          \"value\": \":white_check_mark: - `[CONNECTED] == true`\\n:white_check_mark: - `[STATUS] == 200`\\n\",\n          \"short\": false\n        }\n      ]\n    }\n  ]\n}",
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			body := scenario.Provider.buildRequestBody(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if body != scenario.ExpectedBody {
+				t.Errorf("expected %s, got %s", scenario.ExpectedBody, body)
+			}
+			out := make(map[string]interface{})
+			if err := json.Unmarshal([]byte(body), &out); err != nil {
+				t.Error("expected body to be valid JSON, got error:", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_GetDefaultAlert(t *testing.T) {
+	if (AlertProvider{DefaultAlert: &alert.Alert{}}).GetDefaultAlert() == nil {
+		t.Error("expected default alert to be not nil")
+	}
+	if (AlertProvider{DefaultAlert: nil}).GetDefaultAlert() != nil {
+		t.Error("expected default alert to be nil")
+	}
+}

alerting/provider/teams/teams.go

@@ -0,0 +1,92 @@
+package teams
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+)
+
+// AlertProvider is the configuration necessary for sending an alert using Teams
+type AlertProvider struct {
+	WebhookURL string `yaml:"webhook-url"`
+
+	// DefaultAlert is the default alert configuration to use for endpoints with an alert of the appropriate type
+	DefaultAlert *alert.Alert `yaml:"default-alert"`
+}
+
+// IsValid returns whether the provider's configuration is valid
+func (provider *AlertProvider) IsValid() bool {
+	return len(provider.WebhookURL) > 0
+}
+
+// Send an alert using the provider
+func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) error {
+	buffer := bytes.NewBuffer([]byte(provider.buildRequestBody(endpoint, alert, result, resolved)))
+	request, err := http.NewRequest(http.MethodPost, provider.WebhookURL, buffer)
+	if err != nil {
+		return err
+	}
+	request.Header.Set("Content-Type", "application/json")
+	response, err := client.GetHTTPClient(nil).Do(request)
+	if err != nil {
+		return err
+	}
+	if response.StatusCode > 399 {
+		body, _ := ioutil.ReadAll(response.Body)
+		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
+	}
+	return err
+}
+
+// buildRequestBody builds the request body for the provider
+func (provider *AlertProvider) buildRequestBody(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) string {
+	var message, color string
+	if resolved {
+		message = fmt.Sprintf("An alert for *%s* has been resolved after passing successfully %d time(s) in a row", endpoint.Name, alert.SuccessThreshold)
+		color = "#36A64F"
+	} else {
+		message = fmt.Sprintf("An alert for *%s* has been triggered due to having failed %d time(s) in a row", endpoint.Name, alert.FailureThreshold)
+		color = "#DD0000"
+	}
+	var results string
+	for _, conditionResult := range result.ConditionResults {
+		var prefix string
+		if conditionResult.Success {
+			prefix = "✅"
+		} else {
+			prefix = "❌"
+		}
+		results += fmt.Sprintf("%s - `%s`<br/>", prefix, conditionResult.Condition)
+	}
+	var description string
+	if alertDescription := alert.GetDescription(); len(alertDescription) > 0 {
+		description = ":\\n> " + alertDescription
+	}
+	return fmt.Sprintf(`{
+  "@type": "MessageCard",
+  "@context": "http://schema.org/extensions",
+  "themeColor": "%s",
+  "title": "&#x1F6A8; Gatus",
+  "text": "%s%s",
+  "sections": [
+    {
+      "activityTitle": "URL",
+      "text": "%s"
+    },
+    {
+      "activityTitle": "Condition results",
+      "text": "%s"
+    }
+  ]
+}`, color, message, description, endpoint.URL, results)
+}
+
+// GetDefaultAlert returns the provider's default alert configuration
+func (provider AlertProvider) GetDefaultAlert() *alert.Alert {
+	return provider.DefaultAlert
+}

alerting/provider/teams/teams_test.go

@@ -0,0 +1,158 @@
+package teams
+
+import (
+	"encoding/json"
+	"net/http"
+	"testing"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+	"github.com/TwiN/gatus/v3/test"
+)
+
+func TestAlertProvider_IsValid(t *testing.T) {
+	invalidProvider := AlertProvider{WebhookURL: ""}
+	if invalidProvider.IsValid() {
+		t.Error("provider shouldn't have been valid")
+	}
+	validProvider := AlertProvider{WebhookURL: "http://example.com"}
+	if !validProvider.IsValid() {
+		t.Error("provider should've been valid")
+	}
+}
+
+func TestAlertProvider_Send(t *testing.T) {
+	defer client.InjectHTTPClient(nil)
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name             string
+		Provider         AlertProvider
+		Alert            alert.Alert
+		Resolved         bool
+		MockRoundTripper test.MockRoundTripper
+		ExpectedError    bool
+	}{
+		{
+			Name:     "triggered",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "triggered-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+		{
+			Name:     "resolved",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "resolved-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			client.InjectHTTPClient(&http.Client{Transport: scenario.MockRoundTripper})
+			err := scenario.Provider.Send(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if scenario.ExpectedError && err == nil {
+				t.Error("expected error, got none")
+			}
+			if !scenario.ExpectedError && err != nil {
+				t.Error("expected no error, got", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_buildRequestBody(t *testing.T) {
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name         string
+		Provider     AlertProvider
+		Alert        alert.Alert
+		Resolved     bool
+		ExpectedBody string
+	}{
+		{
+			Name:         "triggered",
+			Provider:     AlertProvider{},
+			Alert:        alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     false,
+			ExpectedBody: "{\n  \"@type\": \"MessageCard\",\n  \"@context\": \"http://schema.org/extensions\",\n  \"themeColor\": \"#DD0000\",\n  \"title\": \"&#x1F6A8; Gatus\",\n  \"text\": \"An alert for *endpoint-name* has been triggered due to having failed 3 time(s) in a row:\\n> description-1\",\n  \"sections\": [\n    {\n      \"activityTitle\": \"URL\",\n      \"text\": \"\"\n    },\n    {\n      \"activityTitle\": \"Condition results\",\n      \"text\": \"&#x274C; - `[CONNECTED] == true`<br/>&#x274C; - `[STATUS] == 200`<br/>\"\n    }\n  ]\n}",
+		},
+		{
+			Name:         "resolved",
+			Provider:     AlertProvider{},
+			Alert:        alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     true,
+			ExpectedBody: "{\n  \"@type\": \"MessageCard\",\n  \"@context\": \"http://schema.org/extensions\",\n  \"themeColor\": \"#36A64F\",\n  \"title\": \"&#x1F6A8; Gatus\",\n  \"text\": \"An alert for *endpoint-name* has been resolved after passing successfully 5 time(s) in a row:\\n> description-2\",\n  \"sections\": [\n    {\n      \"activityTitle\": \"URL\",\n      \"text\": \"\"\n    },\n    {\n      \"activityTitle\": \"Condition results\",\n      \"text\": \"&#x2705; - `[CONNECTED] == true`<br/>&#x2705; - `[STATUS] == 200`<br/>\"\n    }\n  ]\n}",
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			body := scenario.Provider.buildRequestBody(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if body != scenario.ExpectedBody {
+				t.Errorf("expected %s, got %s", scenario.ExpectedBody, body)
+			}
+			out := make(map[string]interface{})
+			if err := json.Unmarshal([]byte(body), &out); err != nil {
+				t.Error("expected body to be valid JSON, got error:", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_GetDefaultAlert(t *testing.T) {
+	if (AlertProvider{DefaultAlert: &alert.Alert{}}).GetDefaultAlert() == nil {
+		t.Error("expected default alert to be not nil")
+	}
+	if (AlertProvider{DefaultAlert: nil}).GetDefaultAlert() != nil {
+		t.Error("expected default alert to be nil")
+	}
+}

alerting/provider/telegram/telegram.go

@@ -0,0 +1,76 @@
+package telegram
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+)
+
+// AlertProvider is the configuration necessary for sending an alert using Telegram
+type AlertProvider struct {
+	Token string `yaml:"token"`
+	ID    string `yaml:"id"`
+
+	// DefaultAlert is the default alert configuration to use for endpoints with an alert of the appropriate type
+	DefaultAlert *alert.Alert `yaml:"default-alert"`
+}
+
+// IsValid returns whether the provider's configuration is valid
+func (provider *AlertProvider) IsValid() bool {
+	return len(provider.Token) > 0 && len(provider.ID) > 0
+}
+
+// Send an alert using the provider
+func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) error {
+	buffer := bytes.NewBuffer([]byte(provider.buildRequestBody(endpoint, alert, result, resolved)))
+	request, err := http.NewRequest(http.MethodPost, fmt.Sprintf("https://api.telegram.org/bot%s/sendMessage", provider.Token), buffer)
+	if err != nil {
+		return err
+	}
+	request.Header.Set("Content-Type", "application/json")
+	response, err := client.GetHTTPClient(nil).Do(request)
+	if err != nil {
+		return err
+	}
+	if response.StatusCode > 399 {
+		body, _ := ioutil.ReadAll(response.Body)
+		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
+	}
+	return err
+}
+
+// buildRequestBody builds the request body for the provider
+func (provider *AlertProvider) buildRequestBody(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) string {
+	var message, results string
+	if resolved {
+		message = fmt.Sprintf("An alert for *%s* has been resolved:\\n—\\n    _healthcheck passing successfully %d time(s) in a row_\\n—  ", endpoint.Name, alert.FailureThreshold)
+	} else {
+		message = fmt.Sprintf("An alert for *%s* has been triggered:\\n—\\n    _healthcheck failed %d time(s) in a row_\\n—  ", endpoint.Name, alert.FailureThreshold)
+	}
+	for _, conditionResult := range result.ConditionResults {
+		var prefix string
+		if conditionResult.Success {
+			prefix = "✅"
+		} else {
+			prefix = "❌"
+		}
+		results += fmt.Sprintf("%s - `%s`\\n", prefix, conditionResult.Condition)
+	}
+	var text string
+	if len(alert.GetDescription()) > 0 {
+		text = fmt.Sprintf("⛑ *Gatus* \\n%s \\n*Description* \\n_%s_  \\n\\n*Condition results*\\n%s", message, alert.GetDescription(), results)
+	} else {
+		text = fmt.Sprintf("⛑ *Gatus* \\n%s \\n*Condition results*\\n%s", message, results)
+	}
+	return fmt.Sprintf(`{"chat_id": "%s", "text": "%s", "parse_mode": "MARKDOWN"}`, provider.ID, text)
+}
+
+// GetDefaultAlert returns the provider's default alert configuration
+func (provider AlertProvider) GetDefaultAlert() *alert.Alert {
+	return provider.DefaultAlert
+}

alerting/provider/telegram/telegram_test.go

@@ -0,0 +1,158 @@
+package telegram
+
+import (
+	"encoding/json"
+	"net/http"
+	"testing"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+	"github.com/TwiN/gatus/v3/test"
+)
+
+func TestAlertProvider_IsValid(t *testing.T) {
+	invalidProvider := AlertProvider{Token: "", ID: ""}
+	if invalidProvider.IsValid() {
+		t.Error("provider shouldn't have been valid")
+	}
+	validProvider := AlertProvider{Token: "123456:ABC-DEF1234ghIkl-zyx57W2v1u123ew11", ID: "12345678"}
+	if !validProvider.IsValid() {
+		t.Error("provider should've been valid")
+	}
+}
+
+func TestAlertProvider_Send(t *testing.T) {
+	defer client.InjectHTTPClient(nil)
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name             string
+		Provider         AlertProvider
+		Alert            alert.Alert
+		Resolved         bool
+		MockRoundTripper test.MockRoundTripper
+		ExpectedError    bool
+	}{
+		{
+			Name:     "triggered",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "triggered-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+		{
+			Name:     "resolved",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "resolved-error",
+			Provider: AlertProvider{},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			client.InjectHTTPClient(&http.Client{Transport: scenario.MockRoundTripper})
+			err := scenario.Provider.Send(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if scenario.ExpectedError && err == nil {
+				t.Error("expected error, got none")
+			}
+			if !scenario.ExpectedError && err != nil {
+				t.Error("expected no error, got", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_buildRequestBody(t *testing.T) {
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name         string
+		Provider     AlertProvider
+		Alert        alert.Alert
+		Resolved     bool
+		ExpectedBody string
+	}{
+		{
+			Name:         "triggered",
+			Provider:     AlertProvider{ID: "123"},
+			Alert:        alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     false,
+			ExpectedBody: "{\"chat_id\": \"123\", \"text\": \"⛑ *Gatus* \\nAn alert for *endpoint-name* has been triggered:\\n—\\n    _healthcheck failed 3 time(s) in a row_\\n—   \\n*Description* \\n_description-1_  \\n\\n*Condition results*\\n❌ - `[CONNECTED] == true`\\n❌ - `[STATUS] == 200`\\n\", \"parse_mode\": \"MARKDOWN\"}",
+		},
+		{
+			Name:         "resolved",
+			Provider:     AlertProvider{ID: "123"},
+			Alert:        alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     true,
+			ExpectedBody: "{\"chat_id\": \"123\", \"text\": \"⛑ *Gatus* \\nAn alert for *endpoint-name* has been resolved:\\n—\\n    _healthcheck passing successfully 3 time(s) in a row_\\n—   \\n*Description* \\n_description-2_  \\n\\n*Condition results*\\n✅ - `[CONNECTED] == true`\\n✅ - `[STATUS] == 200`\\n\", \"parse_mode\": \"MARKDOWN\"}",
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			body := scenario.Provider.buildRequestBody(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if body != scenario.ExpectedBody {
+				t.Errorf("expected %s, got %s", scenario.ExpectedBody, body)
+			}
+			out := make(map[string]interface{})
+			if err := json.Unmarshal([]byte(body), &out); err != nil {
+				t.Error("expected body to be valid JSON, got error:", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_GetDefaultAlert(t *testing.T) {
+	if (AlertProvider{DefaultAlert: &alert.Alert{}}).GetDefaultAlert() == nil {
+		t.Error("expected default alert to be not nil")
+	}
+	if (AlertProvider{DefaultAlert: nil}).GetDefaultAlert() != nil {
+		t.Error("expected default alert to be nil")
+	}
+}

alerting/provider/twilio/twilio.go

@@ -0,0 +1,70 @@
+package twilio
+
+import (
+	"bytes"
+	"encoding/base64"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/client"
+	"github.com/TwiN/gatus/v3/core"
+)
+
+// AlertProvider is the configuration necessary for sending an alert using Twilio
+type AlertProvider struct {
+	SID   string `yaml:"sid"`
+	Token string `yaml:"token"`
+	From  string `yaml:"from"`
+	To    string `yaml:"to"`
+
+	// DefaultAlert is the default alert configuration to use for endpoints with an alert of the appropriate type
+	DefaultAlert *alert.Alert `yaml:"default-alert"`
+}
+
+// IsValid returns whether the provider's configuration is valid
+func (provider *AlertProvider) IsValid() bool {
+	return len(provider.Token) > 0 && len(provider.SID) > 0 && len(provider.From) > 0 && len(provider.To) > 0
+}
+
+// Send an alert using the provider
+func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) error {
+	buffer := bytes.NewBuffer([]byte(provider.buildRequestBody(endpoint, alert, result, resolved)))
+	request, err := http.NewRequest(http.MethodPost, fmt.Sprintf("https://api.twilio.com/2010-04-01/Accounts/%s/Messages.json", provider.SID), buffer)
+	if err != nil {
+		return err
+	}
+	request.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	request.Header.Set("Authorization", fmt.Sprintf("Basic %s", base64.StdEncoding.EncodeToString([]byte(provider.SID+":"+provider.Token))))
+	response, err := client.GetHTTPClient(nil).Do(request)
+	if err != nil {
+		return err
+	}
+	if response.StatusCode > 399 {
+		body, _ := ioutil.ReadAll(response.Body)
+		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
+	}
+	return err
+}
+
+// buildRequestBody builds the request body for the provider
+func (provider *AlertProvider) buildRequestBody(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) string {
+	var message string
+	if resolved {
+		message = fmt.Sprintf("RESOLVED: %s - %s", endpoint.Name, alert.GetDescription())
+	} else {
+		message = fmt.Sprintf("TRIGGERED: %s - %s", endpoint.Name, alert.GetDescription())
+	}
+	return url.Values{
+		"To":   {provider.To},
+		"From": {provider.From},
+		"Body": {message},
+	}.Encode()
+}
+
+// GetDefaultAlert returns the provider's default alert configuration
+func (provider AlertProvider) GetDefaultAlert() *alert.Alert {
+	return provider.DefaultAlert
+}

alerting/provider/twilio/twilio_test.go

@@ -0,0 +1,78 @@
+package twilio
+
+import (
+	"testing"
+
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/core"
+)
+
+func TestTwilioAlertProvider_IsValid(t *testing.T) {
+	invalidProvider := AlertProvider{}
+	if invalidProvider.IsValid() {
+		t.Error("provider shouldn't have been valid")
+	}
+	validProvider := AlertProvider{
+		SID:   "1",
+		Token: "1",
+		From:  "1",
+		To:    "1",
+	}
+	if !validProvider.IsValid() {
+		t.Error("provider should've been valid")
+	}
+}
+
+func TestAlertProvider_buildRequestBody(t *testing.T) {
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name         string
+		Provider     AlertProvider
+		Alert        alert.Alert
+		Resolved     bool
+		ExpectedBody string
+	}{
+		{
+			Name:         "triggered",
+			Provider:     AlertProvider{SID: "1", Token: "2", From: "3", To: "4"},
+			Alert:        alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     false,
+			ExpectedBody: "Body=TRIGGERED%3A+endpoint-name+-+description-1&From=3&To=4",
+		},
+		{
+			Name:         "resolved",
+			Provider:     AlertProvider{SID: "1", Token: "2", From: "3", To: "4"},
+			Alert:        alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     true,
+			ExpectedBody: "Body=RESOLVED%3A+endpoint-name+-+description-2&From=3&To=4",
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			body := scenario.Provider.buildRequestBody(
+				&core.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&core.Result{
+					ConditionResults: []*core.ConditionResult{
+						{Condition: "[CONNECTED] == true", Success: scenario.Resolved},
+						{Condition: "[STATUS] == 200", Success: scenario.Resolved},
+					},
+				},
+				scenario.Resolved,
+			)
+			if body != scenario.ExpectedBody {
+				t.Errorf("expected %s, got %s", scenario.ExpectedBody, body)
+			}
+		})
+	}
+}
+
+func TestAlertProvider_GetDefaultAlert(t *testing.T) {
+	if (AlertProvider{DefaultAlert: &alert.Alert{}}).GetDefaultAlert() == nil {
+		t.Error("expected default alert to be not nil")
+	}
+	if (AlertProvider{DefaultAlert: nil}).GetDefaultAlert() != nil {
+		t.Error("expected default alert to be nil")
+	}
+}

client/client.go

@@ -0,0 +1,117 @@
+package client
+
+import (
+	"crypto/tls"
+	"crypto/x509"
+	"errors"
+	"net"
+	"net/http"
+	"net/smtp"
+	"runtime"
+	"strings"
+	"time"
+
+	"github.com/go-ping/ping"
+)
+
+// injectedHTTPClient is used for testing purposes
+var injectedHTTPClient *http.Client
+
+// GetHTTPClient returns the shared HTTP client
+func GetHTTPClient(config *Config) *http.Client {
+	if injectedHTTPClient != nil {
+		return injectedHTTPClient
+	}
+	if config == nil {
+		return defaultConfig.getHTTPClient()
+	}
+	return config.getHTTPClient()
+}
+
+// CanCreateTCPConnection checks whether a connection can be established with a TCP endpoint
+func CanCreateTCPConnection(address string, config *Config) bool {
+	conn, err := net.DialTimeout("tcp", address, config.Timeout)
+	if err != nil {
+		return false
+	}
+	_ = conn.Close()
+	return true
+}
+
+// CanPerformStartTLS checks whether a connection can be established to an address using the STARTTLS protocol
+func CanPerformStartTLS(address string, config *Config) (connected bool, certificate *x509.Certificate, err error) {
+	hostAndPort := strings.Split(address, ":")
+	if len(hostAndPort) != 2 {
+		return false, nil, errors.New("invalid address for starttls, format must be host:port")
+	}
+	connection, err := net.DialTimeout("tcp", address, config.Timeout)
+	if err != nil {
+		return
+	}
+	smtpClient, err := smtp.NewClient(connection, hostAndPort[0])
+	if err != nil {
+		return
+	}
+	err = smtpClient.StartTLS(&tls.Config{
+		InsecureSkipVerify: config.Insecure,
+		ServerName:         hostAndPort[0],
+	})
+	if err != nil {
+		return
+	}
+	if state, ok := smtpClient.TLSConnectionState(); ok {
+		certificate = state.PeerCertificates[0]
+	} else {
+		return false, nil, errors.New("could not get TLS connection state")
+	}
+	return true, certificate, nil
+}
+
+// CanPerformTLS checks whether a connection can be established to an address using the TLS protocol
+func CanPerformTLS(address string, config *Config) (connected bool, certificate *x509.Certificate, err error) {
+	connection, err := tls.DialWithDialer(&net.Dialer{Timeout: config.Timeout}, "tcp", address, nil)
+	if err != nil {
+		return
+	}
+	defer connection.Close()
+	verifiedChains := connection.ConnectionState().VerifiedChains
+	if len(verifiedChains) == 0 || len(verifiedChains[0]) == 0 {
+		return
+	}
+	return true, verifiedChains[0][0], nil
+}
+
+// Ping checks if an address can be pinged and returns the round-trip time if the address can be pinged
+//
+// Note that this function takes at least 100ms, even if the address is 127.0.0.1
+func Ping(address string, config *Config) (bool, time.Duration) {
+	pinger, err := ping.NewPinger(address)
+	if err != nil {
+		return false, 0
+	}
+	pinger.Count = 1
+	pinger.Timeout = config.Timeout
+	// Set the pinger's privileged mode to true for every GOOS except darwin
+	// See https://github.com/TwiN/gatus/issues/132
+	//
+	// Note that for this to work on Linux, Gatus must run with sudo privileges.
+	// See https://github.com/go-ping/ping#linux
+	pinger.SetPrivileged(runtime.GOOS != "darwin")
+	err = pinger.Run()
+	if err != nil {
+		return false, 0
+	}
+	if pinger.Statistics() != nil {
+		// If the packet loss is 100, it means that the packet didn't reach the host
+		if pinger.Statistics().PacketLoss == 100 {
+			return false, pinger.Timeout
+		}
+		return true, pinger.Statistics().MaxRtt
+	}
+	return true, 0
+}
+
+// InjectHTTPClient is used to inject a custom HTTP client for testing purposes
+func InjectHTTPClient(httpClient *http.Client) {
+	injectedHTTPClient = httpClient
+}

client/client_test.go

@@ -0,0 +1,148 @@
+package client
+
+import (
+	"testing"
+	"time"
+)
+
+func TestGetHTTPClient(t *testing.T) {
+	cfg := &Config{
+		Insecure:       false,
+		IgnoreRedirect: false,
+		Timeout:        0,
+	}
+	cfg.ValidateAndSetDefaults()
+	if GetHTTPClient(cfg) == nil {
+		t.Error("expected client to not be nil")
+	}
+	if GetHTTPClient(nil) == nil {
+		t.Error("expected client to not be nil")
+	}
+}
+
+func TestPing(t *testing.T) {
+	if success, rtt := Ping("127.0.0.1", &Config{Timeout: 500 * time.Millisecond}); !success {
+		t.Error("expected true")
+		if rtt == 0 {
+			t.Error("Round-trip time returned on success should've higher than 0")
+		}
+	}
+	if success, rtt := Ping("256.256.256.256", &Config{Timeout: 500 * time.Millisecond}); success {
+		t.Error("expected false, because the IP is invalid")
+		if rtt != 0 {
+			t.Error("Round-trip time returned on failure should've been 0")
+		}
+	}
+	if success, rtt := Ping("192.168.152.153", &Config{Timeout: 500 * time.Millisecond}); success {
+		t.Error("expected false, because the IP is valid but the host should be unreachable")
+		if rtt != 0 {
+			t.Error("Round-trip time returned on failure should've been 0")
+		}
+	}
+}
+
+func TestCanPerformStartTLS(t *testing.T) {
+	type args struct {
+		address  string
+		insecure bool
+	}
+	tests := []struct {
+		name          string
+		args          args
+		wantConnected bool
+		wantErr       bool
+	}{
+		{
+			name: "invalid address",
+			args: args{
+				address: "test",
+			},
+			wantConnected: false,
+			wantErr:       true,
+		},
+		{
+			name: "error dial",
+			args: args{
+				address: "test:1234",
+			},
+			wantConnected: false,
+			wantErr:       true,
+		},
+		{
+			name: "valid starttls",
+			args: args{
+				address: "smtp.gmail.com:587",
+			},
+			wantConnected: true,
+			wantErr:       false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			connected, _, err := CanPerformStartTLS(tt.args.address, &Config{Insecure: tt.args.insecure, Timeout: 5 * time.Second})
+			if (err != nil) != tt.wantErr {
+				t.Errorf("CanPerformStartTLS() err=%v, wantErr=%v", err, tt.wantErr)
+				return
+			}
+			if connected != tt.wantConnected {
+				t.Errorf("CanPerformStartTLS() connected=%v, wantConnected=%v", connected, tt.wantConnected)
+			}
+		})
+	}
+}
+
+func TestCanPerformTLS(t *testing.T) {
+	type args struct {
+		address  string
+		insecure bool
+	}
+	tests := []struct {
+		name          string
+		args          args
+		wantConnected bool
+		wantErr       bool
+	}{
+		{
+			name: "invalid address",
+			args: args{
+				address: "test",
+			},
+			wantConnected: false,
+			wantErr:       true,
+		},
+		{
+			name: "error dial",
+			args: args{
+				address: "test:1234",
+			},
+			wantConnected: false,
+			wantErr:       true,
+		},
+		{
+			name: "valid tls",
+			args: args{
+				address: "smtp.gmail.com:465",
+			},
+			wantConnected: true,
+			wantErr:       false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			connected, _, err := CanPerformTLS(tt.args.address, &Config{Insecure: tt.args.insecure, Timeout: 5 * time.Second})
+			if (err != nil) != tt.wantErr {
+				t.Errorf("CanPerformTLS() err=%v, wantErr=%v", err, tt.wantErr)
+				return
+			}
+			if connected != tt.wantConnected {
+				t.Errorf("CanPerformTLS() connected=%v, wantConnected=%v", connected, tt.wantConnected)
+			}
+		})
+	}
+}
+
+func TestCanCreateTCPConnection(t *testing.T) {
+	if CanCreateTCPConnection("127.0.0.1", &Config{Timeout: 5 * time.Second}) {
+		t.Error("should've failed, because there's no port in the address")
+	}
+}

client/config.go

@@ -0,0 +1,73 @@
+package client
+
+import (
+	"crypto/tls"
+	"net/http"
+	"time"
+)
+
+const (
+	defaultHTTPTimeout = 10 * time.Second
+)
+
+var (
+	// DefaultConfig is the default client configuration
+	defaultConfig = Config{
+		Insecure:       false,
+		IgnoreRedirect: false,
+		Timeout:        defaultHTTPTimeout,
+	}
+)
+
+// GetDefaultConfig returns a copy of the default configuration
+func GetDefaultConfig() *Config {
+	cfg := defaultConfig
+	return &cfg
+}
+
+// Config is the configuration for clients
+type Config struct {
+	// Insecure determines whether to skip verifying the server's certificate chain and host name
+	Insecure bool `yaml:"insecure"`
+
+	// IgnoreRedirect determines whether to ignore redirects (true) or follow them (false, default)
+	IgnoreRedirect bool `yaml:"ignore-redirect"`
+
+	// Timeout for the client
+	Timeout time.Duration `yaml:"timeout"`
+
+	httpClient *http.Client
+}
+
+// ValidateAndSetDefaults validates the client configuration and sets the default values if necessary
+func (c *Config) ValidateAndSetDefaults() {
+	if c.Timeout < time.Millisecond {
+		c.Timeout = 10 * time.Second
+	}
+}
+
+// GetHTTPClient return an HTTP client matching the Config's parameters.
+func (c *Config) getHTTPClient() *http.Client {
+	if c.httpClient == nil {
+		c.httpClient = &http.Client{
+			Timeout: c.Timeout,
+			Transport: &http.Transport{
+				MaxIdleConns:        100,
+				MaxIdleConnsPerHost: 20,
+				Proxy:               http.ProxyFromEnvironment,
+				TLSClientConfig: &tls.Config{
+					InsecureSkipVerify: c.Insecure,
+				},
+			},
+			CheckRedirect: func(req *http.Request, via []*http.Request) error {
+				if c.IgnoreRedirect {
+					// Don't follow redirects
+					return http.ErrUseLastResponse
+				}
+				// Follow redirects
+				return nil
+			},
+		}
+	}
+	return c.httpClient
+}

client/config_test.go

@@ -0,0 +1,37 @@
+package client
+
+import (
+	"net/http"
+	"testing"
+	"time"
+)
+
+func TestConfig_getHTTPClient(t *testing.T) {
+	insecureConfig := &Config{Insecure: true}
+	insecureConfig.ValidateAndSetDefaults()
+	insecureClient := insecureConfig.getHTTPClient()
+	if !(insecureClient.Transport).(*http.Transport).TLSClientConfig.InsecureSkipVerify {
+		t.Error("expected Config.Insecure set to true to cause the HTTP client to skip certificate verification")
+	}
+	if insecureClient.Timeout != defaultHTTPTimeout {
+		t.Error("expected Config.Timeout to default the HTTP client to a timeout of 10s")
+	}
+	request, _ := http.NewRequest("GET", "", nil)
+	if err := insecureClient.CheckRedirect(request, nil); err != nil {
+		t.Error("expected Config.IgnoreRedirect set to false to cause the HTTP client's CheckRedirect to return nil")
+	}
+
+	secureConfig := &Config{IgnoreRedirect: true, Timeout: 5 * time.Second}
+	secureConfig.ValidateAndSetDefaults()
+	secureClient := secureConfig.getHTTPClient()
+	if (secureClient.Transport).(*http.Transport).TLSClientConfig.InsecureSkipVerify {
+		t.Error("expected Config.Insecure set to false to cause the HTTP client to not skip certificate verification")
+	}
+	if secureClient.Timeout != 5*time.Second {
+		t.Error("expected Config.Timeout to cause the HTTP client to have a timeout of 5s")
+	}
+	request, _ = http.NewRequest("GET", "", nil)
+	if err := secureClient.CheckRedirect(request, nil); err != http.ErrUseLastResponse {
+		t.Error("expected Config.IgnoreRedirect set to true to cause the HTTP client's CheckRedirect to return http.ErrUseLastResponse")
+	}
+}

config.yaml

@@ -1,12 +1,47 @@
-metrics: true
-services:
-  - name: Twinnation
-    url: https://twinnation.org/health
-    interval: 30s
+endpoints:
+  - name: front-end
+    group: core
+    url: "https://twin.sh/health"
+    interval: 5m
     conditions:
       - "[STATUS] == 200"
-  - name: GitHub API
-    url: https://api.github.com/healthz
-    interval: 30s
+      - "[BODY].status == UP"
+      - "[RESPONSE_TIME] < 150"
+
+  - name: back-end
+    group: core
+    url: "https://example.org/"
+    interval: 5m
     conditions:
-      - "[STATUS] == 200"
+      - "[STATUS] == 200"
+      - "[CERTIFICATE_EXPIRATION] > 48h"
+
+  - name: monitoring
+    group: internal
+    url: "https://example.org/"
+    interval: 5m
+    conditions:
+      - "[STATUS] == 200"
+
+  - name: nas
+    group: internal
+    url: "https://example.org/"
+    interval: 5m
+    conditions:
+      - "[STATUS] == 200"
+
+  - name: example-dns-query
+    url: "8.8.8.8" # Address of the DNS server to use
+    interval: 5m
+    dns:
+      query-name: "example.com"
+      query-type: "A"
+    conditions:
+      - "[BODY] == 93.184.216.34"
+      - "[DNS_RCODE] == NOERROR"
+
+  - name: icmp-ping
+    url: "icmp://example.org"
+    interval: 1m
+    conditions:
+      - "[CONNECTED] == true"

config/config.go

@@ -2,56 +2,142 @@ package config
 
 import (
 	"errors"
-	"github.com/TwinProduction/gatus/core"
-	"gopkg.in/yaml.v2"
 	"io/ioutil"
 	"log"
 	"os"
 	"time"
+
+	"github.com/TwiN/gatus/v3/alerting"
+	"github.com/TwiN/gatus/v3/alerting/alert"
+	"github.com/TwiN/gatus/v3/alerting/provider"
+	"github.com/TwiN/gatus/v3/config/maintenance"
+	"github.com/TwiN/gatus/v3/config/ui"
+	"github.com/TwiN/gatus/v3/config/web"
+	"github.com/TwiN/gatus/v3/core"
+	"github.com/TwiN/gatus/v3/security"
+	"github.com/TwiN/gatus/v3/storage"
+	"gopkg.in/yaml.v2"
 )
 
-type Config struct {
-	Metrics  bool            `yaml:"metrics"`
-	Services []*core.Service `yaml:"services"`
-}
+const (
+	// DefaultConfigurationFilePath is the default path that will be used to search for the configuration file
+	// if a custom path isn't configured through the GATUS_CONFIG_FILE environment variable
+	DefaultConfigurationFilePath = "config/config.yaml"
+
+	// DefaultFallbackConfigurationFilePath is the default fallback path that will be used to search for the
+	// configuration file if DefaultConfigurationFilePath didn't work
+	DefaultFallbackConfigurationFilePath = "config/config.yml"
+)
 
 var (
-	ErrNoServiceInConfig  = errors.New("configuration file should contain at least 1 service")
+	// ErrNoEndpointInConfig is an error returned when a configuration file has no endpoints configured
+	ErrNoEndpointInConfig = errors.New("configuration file should contain at least 1 endpoint")
+
+	// ErrConfigFileNotFound is an error returned when the configuration file could not be found
 	ErrConfigFileNotFound = errors.New("configuration file not found")
-	ErrConfigNotLoaded    = errors.New("configuration is nil")
-	config                *Config
+
+	// ErrInvalidSecurityConfig is an error returned when the security configuration is invalid
+	ErrInvalidSecurityConfig = errors.New("invalid security configuration")
 )
 
-func Get() *Config {
-	if config == nil {
-		panic(ErrConfigNotLoaded)
-	}
-	return config
+// Config is the main configuration structure
+type Config struct {
+	// Debug Whether to enable debug logs
+	Debug bool `yaml:"debug,omitempty"`
+
+	// Metrics Whether to expose metrics at /metrics
+	Metrics bool `yaml:"metrics,omitempty"`
+
+	// SkipInvalidConfigUpdate Whether to make the application ignore invalid configuration
+	// if the configuration file is updated while the application is running
+	SkipInvalidConfigUpdate bool `yaml:"skip-invalid-config-update,omitempty"`
+
+	// DisableMonitoringLock Whether to disable the monitoring lock
+	// The monitoring lock is what prevents multiple endpoints from being processed at the same time.
+	// Disabling this may lead to inaccurate response times
+	DisableMonitoringLock bool `yaml:"disable-monitoring-lock,omitempty"`
+
+	// Security Configuration for securing access to Gatus
+	Security *security.Config `yaml:"security,omitempty"`
+
+	// Alerting Configuration for alerting
+	Alerting *alerting.Config `yaml:"alerting,omitempty"`
+
+	// Endpoints List of endpoints to monitor
+	Endpoints []*core.Endpoint `yaml:"endpoints,omitempty"`
+
+	// Services List of endpoints to monitor
+	//
+	// XXX: Remove this in v5.0.0
+	// XXX: This is not a typo -- not v4.0.0, but v5.0.0 -- I want to give enough time for people to migrate
+	//
+	// Deprecated in favor of Endpoints
+	Services []*core.Endpoint `yaml:"services,omitempty"`
+
+	// Storage is the configuration for how the data is stored
+	Storage *storage.Config `yaml:"storage,omitempty"`
+
+	// Web is the web configuration for the application
+	Web *web.Config `yaml:"web,omitempty"`
+
+	// UI is the configuration for the UI
+	UI *ui.Config `yaml:"ui,omitempty"`
+
+	// Maintenance is the configuration for creating a maintenance window in which no alerts are sent
+	Maintenance *maintenance.Config `yaml:"maintenance,omitempty"`
+
+	filePath        string    // path to the file from which config was loaded from
+	lastFileModTime time.Time // last modification time
 }
 
-func Load(configFile string) error {
-	log.Printf("[config][Load] Attempting to load config from configFile=%s", configFile)
+// HasLoadedConfigurationFileBeenModified returns whether the file that the
+// configuration has been loaded from has been modified since it was last read
+func (config Config) HasLoadedConfigurationFileBeenModified() bool {
+	if fileInfo, err := os.Stat(config.filePath); err == nil {
+		if !fileInfo.ModTime().IsZero() {
+			return config.lastFileModTime.Unix() != fileInfo.ModTime().Unix()
+		}
+	}
+	return false
+}
+
+// UpdateLastFileModTime refreshes Config.lastFileModTime
+func (config *Config) UpdateLastFileModTime() {
+	if fileInfo, err := os.Stat(config.filePath); err == nil {
+		if !fileInfo.ModTime().IsZero() {
+			config.lastFileModTime = fileInfo.ModTime()
+		}
+	} else {
+		log.Println("[config][UpdateLastFileModTime] Ran into error updating lastFileModTime:", err.Error())
+	}
+}
+
+// Load loads a custom configuration file
+// Note that the misconfiguration of some fields may lead to panics. This is on purpose.
+func Load(configFile string) (*Config, error) {
+	log.Printf("[config][Load] Reading configuration from configFile=%s", configFile)
 	cfg, err := readConfigurationFile(configFile)
 	if err != nil {
 		if os.IsNotExist(err) {
-			return ErrConfigFileNotFound
-		} else {
-			return err
+			return nil, ErrConfigFileNotFound
 		}
+		return nil, err
 	}
-	config = cfg
-	return nil
+	cfg.filePath = configFile
+	cfg.UpdateLastFileModTime()
+	return cfg, nil
 }
 
-func LoadDefaultConfiguration() error {
-	err := Load("config/config.yaml")
+// LoadDefaultConfiguration loads the default configuration file
+func LoadDefaultConfiguration() (*Config, error) {
+	cfg, err := Load(DefaultConfigurationFilePath)
 	if err != nil {
 		if err == ErrConfigFileNotFound {
-			return Load("config/config.yml")
+			return Load(DefaultFallbackConfigurationFilePath)
 		}
-		return err
+		return nil, err
 	}
-	return nil
+	return cfg, nil
 }
 
 func readConfigurationFile(fileName string) (config *Config, err error) {
@@ -63,21 +149,166 @@ func readConfigurationFile(fileName string) (config *Config, err error) {
 	return
 }
 
+// parseAndValidateConfigBytes parses a Gatus configuration file into a Config struct and validates its parameters
 func parseAndValidateConfigBytes(yamlBytes []byte) (config *Config, err error) {
 	// Expand environment variables
 	yamlBytes = []byte(os.ExpandEnv(string(yamlBytes)))
 	// Parse configuration file
-	err = yaml.Unmarshal(yamlBytes, &config)
-	// Check if the configuration file at least has services.
-	if config == nil || len(config.Services) == 0 {
-		err = ErrNoServiceInConfig
+	if err = yaml.Unmarshal(yamlBytes, &config); err != nil {
+		return
+	}
+	if config != nil && len(config.Services) > 0 { // XXX: Remove this in v5.0.0
+		log.Println("WARNING: Your configuration is using 'services:', which is deprecated in favor of 'endpoints:'.")
+		log.Println("WARNING: See https://github.com/TwiN/gatus/issues/191 for more information")
+		config.Endpoints = append(config.Endpoints, config.Services...)
+		config.Services = nil
+	}
+	// Check if the configuration file at least has endpoints configured
+	if config == nil || config.Endpoints == nil || len(config.Endpoints) == 0 {
+		err = ErrNoEndpointInConfig
 	} else {
-		// Set the default values if they aren't set
-		for _, service := range config.Services {
-			if service.Interval == 0 {
-				service.Interval = 10 * time.Second
-			}
+		validateAlertingConfig(config.Alerting, config.Endpoints, config.Debug)
+		if err := validateSecurityConfig(config); err != nil {
+			return nil, err
+		}
+		if err := validateEndpointsConfig(config); err != nil {
+			return nil, err
+		}
+		if err := validateWebConfig(config); err != nil {
+			return nil, err
+		}
+		if err := validateUIConfig(config); err != nil {
+			return nil, err
+		}
+		if err := validateMaintenanceConfig(config); err != nil {
+			return nil, err
+		}
+		if err := validateStorageConfig(config); err != nil {
+			return nil, err
 		}
 	}
 	return
 }
+
+func validateStorageConfig(config *Config) error {
+	if config.Storage == nil {
+		config.Storage = &storage.Config{
+			Type: storage.TypeMemory,
+		}
+	} else {
+		if err := config.Storage.ValidateAndSetDefaults(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func validateMaintenanceConfig(config *Config) error {
+	if config.Maintenance == nil {
+		config.Maintenance = maintenance.GetDefaultConfig()
+	} else {
+		if err := config.Maintenance.ValidateAndSetDefaults(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func validateUIConfig(config *Config) error {
+	if config.UI == nil {
+		config.UI = ui.GetDefaultConfig()
+	} else {
+		if err := config.UI.ValidateAndSetDefaults(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func validateWebConfig(config *Config) error {
+	if config.Web == nil {
+		config.Web = web.GetDefaultConfig()
+	} else {
+		return config.Web.ValidateAndSetDefaults()
+	}
+	return nil
+}
+
+func validateEndpointsConfig(config *Config) error {
+	for _, endpoint := range config.Endpoints {
+		if config.Debug {
+			log.Printf("[config][validateEndpointsConfig] Validating endpoint '%s'", endpoint.Name)
+		}
+		if err := endpoint.ValidateAndSetDefaults(); err != nil {
+			return err
+		}
+	}
+	log.Printf("[config][validateEndpointsConfig] Validated %d endpoints", len(config.Endpoints))
+	return nil
+}
+
+func validateSecurityConfig(config *Config) error {
+	if config.Security != nil {
+		if config.Security.IsValid() {
+			if config.Debug {
+				log.Printf("[config][validateSecurityConfig] Basic security configuration has been validated")
+			}
+		} else {
+			// If there was an attempt to configure security, then it must mean that some confidential or private
+			// data are exposed. As a result, we'll force a panic because it's better to be safe than sorry.
+			return ErrInvalidSecurityConfig
+		}
+	}
+	return nil
+}
+
+// validateAlertingConfig validates the alerting configuration
+// Note that the alerting configuration has to be validated before the endpoint configuration, because the default alert
+// returned by provider.AlertProvider.GetDefaultAlert() must be parsed before core.Endpoint.ValidateAndSetDefaults()
+// sets the default alert values when none are set.
+func validateAlertingConfig(alertingConfig *alerting.Config, endpoints []*core.Endpoint, debug bool) {
+	if alertingConfig == nil {
+		log.Printf("[config][validateAlertingConfig] Alerting is not configured")
+		return
+	}
+	alertTypes := []alert.Type{
+		alert.TypeCustom,
+		alert.TypeDiscord,
+		alert.TypeEmail,
+		alert.TypeMattermost,
+		alert.TypeMessagebird,
+		alert.TypePagerDuty,
+		alert.TypeSlack,
+		alert.TypeTeams,
+		alert.TypeTelegram,
+		alert.TypeTwilio,
+	}
+	var validProviders, invalidProviders []alert.Type
+	for _, alertType := range alertTypes {
+		alertProvider := alertingConfig.GetAlertingProviderByAlertType(alertType)
+		if alertProvider != nil {
+			if alertProvider.IsValid() {
+				// Parse alerts with the provider's default alert
+				if alertProvider.GetDefaultAlert() != nil {
+					for _, endpoint := range endpoints {
+						for alertIndex, endpointAlert := range endpoint.Alerts {
+							if alertType == endpointAlert.Type {
+								if debug {
+									log.Printf("[config][validateAlertingConfig] Parsing alert %d with provider's default alert for provider=%s in endpoint=%s", alertIndex, alertType, endpoint.Name)
+								}
+								provider.ParseWithDefaultAlert(alertProvider.GetDefaultAlert(), endpointAlert)
+							}
+						}
+					}
+				}
+				validProviders = append(validProviders, alertType)
+			} else {
+				log.Printf("[config][validateAlertingConfig] Ignoring provider=%s because configuration is invalid", alertType)
+				invalidProviders = append(invalidProviders, alertType)
+			}
+		} else {
+			invalidProviders = append(invalidProviders, alertType)
+		}
+	}
+	log.Printf("[config][validateAlertingConfig] configuredProviders=%s; ignoredProviders=%s", validProviders, invalidProviders)
+}

config/maintenance/maintenance.go

@@ -0,0 +1,145 @@
+package maintenance
+
+import (
+	"errors"
+	"fmt"
+	"strconv"
+	"strings"
+	"time"
+)
+
+var (
+	errInvalidMaintenanceStartFormat = errors.New("invalid maintenance start format: must be hh:mm, between 00:00 and 23:59 inclusively (e.g. 23:00)")
+	errInvalidMaintenanceDuration    = errors.New("invalid maintenance duration: must be bigger than 0 (e.g. 30m)")
+	errInvalidDayName                = fmt.Errorf("invalid value specified for 'on'. supported values are %s", longDayNames)
+
+	longDayNames = []string{
+		"Sunday",
+		"Monday",
+		"Tuesday",
+		"Wednesday",
+		"Thursday",
+		"Friday",
+		"Saturday",
+	}
+)
+
+// Config allows for the configuration of a maintenance period.
+// During this maintenance period, no alerts will be sent.
+//
+// Uses UTC.
+type Config struct {
+	Enabled  *bool         `yaml:"enabled"`  // Whether the maintenance period is enabled. Enabled by default if nil.
+	Start    string        `yaml:"start"`    // Time at which the maintenance period starts (e.g. 23:00)
+	Duration time.Duration `yaml:"duration"` // Duration of the maintenance period (e.g. 4h)
+
+	// Every is a list of days of the week during which maintenance period applies.
+	// See longDayNames for list of valid values.
+	// Every day if empty.
+	Every []string `yaml:"every"`
+
+	durationToStartFromMidnight time.Duration
+}
+
+func GetDefaultConfig() *Config {
+	defaultValue := false
+	return &Config{
+		Enabled: &defaultValue,
+	}
+}
+
+// IsEnabled returns whether maintenance is enabled or not
+func (c Config) IsEnabled() bool {
+	if c.Enabled == nil {
+		return true
+	}
+	return *c.Enabled
+}
+
+// ValidateAndSetDefaults validates the maintenance configuration and sets the default values if necessary.
+//
+// Must be called once in the application's lifecycle before IsUnderMaintenance is called, since it
+// also sets durationToStartFromMidnight.
+func (c *Config) ValidateAndSetDefaults() error {
+	if c == nil || !c.IsEnabled() {
+		// Don't waste time validating if maintenance is not enabled.
+		return nil
+	}
+	for _, day := range c.Every {
+		isDayValid := false
+		for _, longDayName := range longDayNames {
+			if day == longDayName {
+				isDayValid = true
+				break
+			}
+		}
+		if !isDayValid {
+			return errInvalidDayName
+		}
+	}
+	var err error
+	c.durationToStartFromMidnight, err = hhmmToDuration(c.Start)
+	if err != nil {
+		return err
+	}
+	if c.Duration <= 0 || c.Duration >= 24*time.Hour {
+		return errInvalidMaintenanceDuration
+	}
+	return nil
+}
+
+// IsUnderMaintenance checks whether the endpoints that Gatus monitors are within the configured maintenance window
+func (c Config) IsUnderMaintenance() bool {
+	if !c.IsEnabled() {
+		return false
+	}
+	now := time.Now().UTC()
+	var dayWhereMaintenancePeriodWouldStart time.Time
+	if now.Hour() >= int(c.durationToStartFromMidnight.Hours()) {
+		dayWhereMaintenancePeriodWouldStart = now.Truncate(24 * time.Hour)
+	} else {
+		dayWhereMaintenancePeriodWouldStart = now.Add(-c.Duration).Truncate(24 * time.Hour)
+	}
+	hasMaintenanceEveryDay := len(c.Every) == 0
+	hasMaintenancePeriodScheduledToStartOnThatWeekday := c.hasDay(dayWhereMaintenancePeriodWouldStart.Weekday().String())
+	if !hasMaintenanceEveryDay && !hasMaintenancePeriodScheduledToStartOnThatWeekday {
+		// The day when the maintenance period would start is not scheduled
+		// to have any maintenance, so we can just return false.
+		return false
+	}
+	startOfMaintenancePeriod := dayWhereMaintenancePeriodWouldStart.Add(c.durationToStartFromMidnight)
+	endOfMaintenancePeriod := startOfMaintenancePeriod.Add(c.Duration)
+	return now.After(startOfMaintenancePeriod) && now.Before(endOfMaintenancePeriod)
+}
+
+func (c Config) hasDay(day string) bool {
+	for _, d := range c.Every {
+		if d == day {
+			return true
+		}
+	}
+	return false
+}
+
+func hhmmToDuration(s string) (time.Duration, error) {
+	if len(s) != 5 {
+		return 0, errInvalidMaintenanceStartFormat
+	}
+	var hours, minutes int
+	var err error
+	if hours, err = extractNumericalValueFromPotentiallyZeroPaddedString(s[:2]); err != nil {
+		return 0, err
+	}
+	if minutes, err = extractNumericalValueFromPotentiallyZeroPaddedString(s[3:5]); err != nil {
+		return 0, err
+	}
+	duration := (time.Duration(hours) * time.Hour) + (time.Duration(minutes) * time.Minute)
+	if hours < 0 || hours > 23 || minutes < 0 || minutes > 59 || duration < 0 || duration >= 24*time.Hour {
+		return 0, errInvalidMaintenanceStartFormat
+	}
+	return duration, nil
+}
+
+func extractNumericalValueFromPotentiallyZeroPaddedString(s string) (int, error) {
+	return strconv.Atoi(strings.TrimPrefix(s, "0"))
+}

config/maintenance/maintenance_test.go

@@ -0,0 +1,226 @@
+package maintenance
+
+import (
+	"errors"
+	"fmt"
+	"strconv"
+	"testing"
+	"time"
+)
+
+func TestGetDefaultConfig(t *testing.T) {
+	if *GetDefaultConfig().Enabled {
+		t.Fatal("expected default config to be disabled by default")
+	}
+}
+
+func TestConfig_ValidateAndSetDefaults(t *testing.T) {
+	yes, no := true, false
+	scenarios := []struct {
+		name          string
+		cfg           *Config
+		expectedError error
+	}{
+		{
+			name:          "nil",
+			cfg:           nil,
+			expectedError: nil,
+		},
+		{
+			name: "disabled",
+			cfg: &Config{
+				Enabled: &no,
+			},
+			expectedError: nil,
+		},
+		{
+			name: "invalid-day",
+			cfg: &Config{
+				Every: []string{"invalid-day"},
+			},
+			expectedError: errInvalidDayName,
+		},
+		{
+			name: "invalid-day",
+			cfg: &Config{
+				Every: []string{"invalid-day"},
+			},
+			expectedError: errInvalidDayName,
+		},
+		{
+			name: "invalid-start-format",
+			cfg: &Config{
+				Start: "0000",
+			},
+			expectedError: errInvalidMaintenanceStartFormat,
+		},
+		{
+			name: "invalid-start-hours",
+			cfg: &Config{
+				Start: "25:00",
+			},
+			expectedError: errInvalidMaintenanceStartFormat,
+		},
+		{
+			name: "invalid-start-minutes",
+			cfg: &Config{
+				Start: "0:61",
+			},
+			expectedError: errInvalidMaintenanceStartFormat,
+		},
+		{
+			name: "invalid-start-minutes-non-numerical",
+			cfg: &Config{
+				Start: "00:zz",
+			},
+			expectedError: strconv.ErrSyntax,
+		},
+		{
+			name: "invalid-start-hours-non-numerical",
+			cfg: &Config{
+				Start: "zz:00",
+			},
+			expectedError: strconv.ErrSyntax,
+		},
+		{
+			name: "invalid-duration",
+			cfg: &Config{
+				Start:    "23:00",
+				Duration: 0,
+			},
+			expectedError: errInvalidMaintenanceDuration,
+		},
+		{
+			name: "every-day-at-2300",
+			cfg: &Config{
+				Start:    "23:00",
+				Duration: time.Hour,
+			},
+			expectedError: nil,
+		},
+		{
+			name: "every-monday-at-0000",
+			cfg: &Config{
+				Start:    "00:00",
+				Duration: 30 * time.Minute,
+				Every:    []string{"Monday"},
+			},
+			expectedError: nil,
+		},
+		{
+			name: "every-friday-and-sunday-at-0000-explicitly-enabled",
+			cfg: &Config{
+				Enabled:  &yes,
+				Start:    "08:00",
+				Duration: 8 * time.Hour,
+				Every:    []string{"Friday", "Sunday"},
+			},
+			expectedError: nil,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.name, func(t *testing.T) {
+			err := scenario.cfg.ValidateAndSetDefaults()
+			if !errors.Is(err, scenario.expectedError) {
+				t.Errorf("expected %v, got %v", scenario.expectedError, err)
+			}
+		})
+	}
+}
+
+func TestConfig_IsUnderMaintenance(t *testing.T) {
+	yes, no := true, false
+	now := time.Now().UTC()
+	scenarios := []struct {
+		name     string
+		cfg      *Config
+		expected bool
+	}{
+		{
+			name: "disabled",
+			cfg: &Config{
+				Enabled: &no,
+			},
+			expected: false,
+		},
+		{
+			name: "under-maintenance-explicitly-enabled",
+			cfg: &Config{
+				Enabled:  &yes,
+				Start:    fmt.Sprintf("%02d:00", now.Hour()),
+				Duration: 2 * time.Hour,
+			},
+			expected: true,
+		},
+		{
+			name: "under-maintenance-starting-now-for-2h",
+			cfg: &Config{
+				Start:    fmt.Sprintf("%02d:00", now.Hour()),
+				Duration: 2 * time.Hour,
+			},
+			expected: true,
+		},
+		{
+			name: "under-maintenance-starting-now-for-8h",
+			cfg: &Config{
+				Start:    fmt.Sprintf("%02d:00", now.Hour()),
+				Duration: 8 * time.Hour,
+			},
+			expected: true,
+		},
+		{
+			name: "under-maintenance-starting-4h-ago-for-8h",
+			cfg: &Config{
+				Start:    fmt.Sprintf("%02d:00", normalizeHour(now.Hour()-4)),
+				Duration: 8 * time.Hour,
+			},
+			expected: true,
+		},
+		{
+			name: "under-maintenance-starting-4h-ago-for-3h",
+			cfg: &Config{
+				Start:    fmt.Sprintf("%02d:00", normalizeHour(now.Hour()-4)),
+				Duration: 3 * time.Hour,
+			},
+			expected: false,
+		},
+		{
+			name: "under-maintenance-starting-5h-ago-for-1h",
+			cfg: &Config{
+				Start:    fmt.Sprintf("%02d:00", normalizeHour(now.Hour()-5)),
+				Duration: time.Hour,
+			},
+			expected: false,
+		},
+		{
+			name: "not-under-maintenance-today",
+			cfg: &Config{
+				Start:    fmt.Sprintf("%02d:00", now.Hour()),
+				Duration: time.Hour,
+				Every:    []string{now.Add(48 * time.Hour).Weekday().String()},
+			},
+			expected: false,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.name, func(t *testing.T) {
+			t.Log(scenario.cfg.Start)
+			t.Log(now)
+			if err := scenario.cfg.ValidateAndSetDefaults(); err != nil {
+				t.Fatal("validation shouldn't have returned an error, got", err)
+			}
+			isUnderMaintenance := scenario.cfg.IsUnderMaintenance()
+			if isUnderMaintenance != scenario.expected {
+				t.Errorf("expected %v, got %v", scenario.expected, isUnderMaintenance)
+				t.Logf("start=%v; duration=%v; now=%v", scenario.cfg.Start, scenario.cfg.Duration, time.Now().UTC())
+			}
+		})
+	}
+}
+
+func normalizeHour(hour int) int {
+	if hour < 0 {
+		return hour + 24
+	}
+	return hour
+}

config/ui/ui.go

@@ -0,0 +1,48 @@
+package ui
+
+import (
+	"bytes"
+	"html/template"
+)
+
+const (
+	defaultTitle = "Health Dashboard | Gatus"
+	defaultLogo  = ""
+)
+
+var (
+	// StaticFolder is the path to the location of the static folder from the root path of the project
+	// The only reason this is exposed is to allow running tests from a different path than the root path of the project
+	StaticFolder = "./web/static"
+)
+
+// Config is the configuration for the UI of Gatus
+type Config struct {
+	Title string `yaml:"title"` // Title of the page
+	Logo  string `yaml:"logo"`  // Logo to display on the page
+}
+
+// GetDefaultConfig returns a Config struct with the default values
+func GetDefaultConfig() *Config {
+	return &Config{
+		Title: defaultTitle,
+		Logo:  defaultLogo,
+	}
+}
+
+// ValidateAndSetDefaults validates the UI configuration and sets the default values if necessary.
+func (cfg *Config) ValidateAndSetDefaults() error {
+	if len(cfg.Title) == 0 {
+		cfg.Title = defaultTitle
+	}
+	t, err := template.ParseFiles(StaticFolder + "/index.html")
+	if err != nil {
+		return err
+	}
+	var buffer bytes.Buffer
+	err = t.Execute(&buffer, cfg)
+	if err != nil {
+		return err
+	}
+	return nil
+}

config/ui/ui_test.go

@@ -0,0 +1,26 @@
+package ui
+
+import (
+	"testing"
+)
+
+func TestConfig_ValidateAndSetDefaults(t *testing.T) {
+	StaticFolder = "../../web/static"
+	defer func() {
+		StaticFolder = "./web/static"
+	}()
+	cfg := &Config{Title: ""}
+	if err := cfg.ValidateAndSetDefaults(); err != nil {
+		t.Error("expected no error, got", err.Error())
+	}
+}
+
+func TestGetDefaultConfig(t *testing.T) {
+	defaultConfig := GetDefaultConfig()
+	if defaultConfig.Title != defaultTitle {
+		t.Error("expected GetDefaultConfig() to return defaultTitle, got", defaultConfig.Title)
+	}
+	if defaultConfig.Logo != defaultLogo {
+		t.Error("expected GetDefaultConfig() to return defaultLogo, got", defaultConfig.Logo)
+	}
+}

config/web/web.go

@@ -0,0 +1,49 @@
+package web
+
+import (
+	"fmt"
+	"math"
+)
+
+const (
+	// DefaultAddress is the default address the application will bind to
+	DefaultAddress = "0.0.0.0"
+
+	// DefaultPort is the default port the application will listen on
+	DefaultPort = 8080
+)
+
+// Config is the structure which supports the configuration of the endpoint
+// which provides access to the web frontend
+type Config struct {
+	// Address to listen on (defaults to 0.0.0.0 specified by DefaultAddress)
+	Address string `yaml:"address"`
+
+	// Port to listen on (default to 8080 specified by DefaultPort)
+	Port int `yaml:"port"`
+}
+
+// GetDefaultConfig returns a Config struct with the default values
+func GetDefaultConfig() *Config {
+	return &Config{Address: DefaultAddress, Port: DefaultPort}
+}
+
+// ValidateAndSetDefaults validates the web configuration and sets the default values if necessary.
+func (web *Config) ValidateAndSetDefaults() error {
+	// Validate the Address
+	if len(web.Address) == 0 {
+		web.Address = DefaultAddress
+	}
+	// Validate the Port
+	if web.Port == 0 {
+		web.Port = DefaultPort
+	} else if web.Port < 0 || web.Port > math.MaxUint16 {
+		return fmt.Errorf("invalid port: value should be between %d and %d", 0, math.MaxUint16)
+	}
+	return nil
+}
+
+// SocketAddress returns the combination of the Address and the Port
+func (web *Config) SocketAddress() string {
+	return fmt.Sprintf("%s:%d", web.Address, web.Port)
+}

config/web/web_test.go

@@ -0,0 +1,65 @@
+package web
+
+import (
+	"testing"
+)
+
+func TestGetDefaultConfig(t *testing.T) {
+	defaultConfig := GetDefaultConfig()
+	if defaultConfig.Port != DefaultPort {
+		t.Error("expected default config to have the default port")
+	}
+	if defaultConfig.Address != DefaultAddress {
+		t.Error("expected default config to have the default address")
+	}
+}
+
+func TestConfig_ValidateAndSetDefaults(t *testing.T) {
+	scenarios := []struct {
+		name            string
+		cfg             *Config
+		expectedAddress string
+		expectedPort    int
+		expectedErr     bool
+	}{
+		{
+			name:            "no-explicit-config",
+			cfg:             &Config{},
+			expectedAddress: "0.0.0.0",
+			expectedPort:    8080,
+			expectedErr:     false,
+		},
+		{
+			name:        "invalid-port",
+			cfg:         &Config{Port: 100000000},
+			expectedErr: true,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.name, func(t *testing.T) {
+			err := scenario.cfg.ValidateAndSetDefaults()
+			if (err != nil) != scenario.expectedErr {
+				t.Errorf("expected the existence of an error to be %v, got %v", scenario.expectedErr, err)
+				return
+			}
+			if !scenario.expectedErr {
+				if scenario.cfg.Port != scenario.expectedPort {
+					t.Errorf("expected port to be %d, got %d", scenario.expectedPort, scenario.cfg.Port)
+				}
+				if scenario.cfg.Address != scenario.expectedAddress {
+					t.Errorf("expected address to be %s, got %s", scenario.expectedAddress, scenario.cfg.Address)
+				}
+			}
+		})
+	}
+}
+
+func TestConfig_SocketAddress(t *testing.T) {
+	web := &Config{
+		Address: "0.0.0.0",
+		Port:    8081,
+	}
+	if web.SocketAddress() != "0.0.0.0:8081" {
+		t.Errorf("expected %s, got %s", "0.0.0.0:8081", web.SocketAddress())
+	}
+}

controller/controller.go

@@ -0,0 +1,49 @@
+package controller
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"time"
+
+	"github.com/TwiN/gatus/v3/config/ui"
+	"github.com/TwiN/gatus/v3/config/web"
+	"github.com/TwiN/gatus/v3/controller/handler"
+	"github.com/TwiN/gatus/v3/security"
+)
+
+var (
+	// server is the http.Server created by Handle.
+	// The only reason it exists is for testing purposes.
+	server *http.Server
+)
+
+// Handle creates the router and starts the server
+func Handle(securityConfig *security.Config, webConfig *web.Config, uiConfig *ui.Config, enableMetrics bool) {
+	var router http.Handler = handler.CreateRouter(ui.StaticFolder, securityConfig, uiConfig, enableMetrics)
+	if os.Getenv("ENVIRONMENT") == "dev" {
+		router = handler.DevelopmentCORS(router)
+	}
+	server = &http.Server{
+		Addr:         fmt.Sprintf("%s:%d", webConfig.Address, webConfig.Port),
+		Handler:      router,
+		ReadTimeout:  15 * time.Second,
+		WriteTimeout: 15 * time.Second,
+		IdleTimeout:  15 * time.Second,
+	}
+	log.Println("[controller][Handle] Listening on " + webConfig.SocketAddress())
+	if os.Getenv("ROUTER_TEST") == "true" {
+		return
+	}
+	log.Println("[controller][Handle]", server.ListenAndServe())
+}
+
+// Shutdown stops the server
+func Shutdown() {
+	if server != nil {
+		_ = server.Shutdown(context.TODO())
+		server = nil
+	}
+}

controller/controller_test.go

@@ -0,0 +1,55 @@
+package controller
+
+import (
+	"math/rand"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"testing"
+
+	"github.com/TwiN/gatus/v3/config"
+	"github.com/TwiN/gatus/v3/config/web"
+	"github.com/TwiN/gatus/v3/core"
+)
+
+func TestHandle(t *testing.T) {
+	cfg := &config.Config{
+		Web: &web.Config{
+			Address: "0.0.0.0",
+			Port:    rand.Intn(65534),
+		},
+		Endpoints: []*core.Endpoint{
+			{
+				Name:  "frontend",
+				Group: "core",
+			},
+			{
+				Name:  "backend",
+				Group: "core",
+			},
+		},
+	}
+	_ = os.Setenv("ROUTER_TEST", "true")
+	_ = os.Setenv("ENVIRONMENT", "dev")
+	defer os.Clearenv()
+	Handle(cfg.Security, cfg.Web, cfg.UI, cfg.Metrics)
+	defer Shutdown()
+	request, _ := http.NewRequest("GET", "/health", http.NoBody)
+	responseRecorder := httptest.NewRecorder()
+	server.Handler.ServeHTTP(responseRecorder, request)
+	if responseRecorder.Code != http.StatusOK {
+		t.Error("expected GET /health to return status code 200")
+	}
+	if server == nil {
+		t.Fatal("server should've been set (but because we set ROUTER_TEST, it shouldn't have been started)")
+	}
+}
+
+func TestShutdown(t *testing.T) {
+	// Pretend that we called controller.Handle(), which initializes the server variable
+	server = &http.Server{}
+	Shutdown()
+	if server != nil {
+		t.Error("server should've been shut down")
+	}
+}

controller/handler/badge.go

@@ -0,0 +1,225 @@
+package handler
+
+import (
+	"fmt"
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/TwiN/gatus/v3/storage/store"
+	"github.com/TwiN/gatus/v3/storage/store/common"
+	"github.com/gorilla/mux"
+)
+
+const (
+	badgeColorHexAwesome  = "#40cc11"
+	badgeColorHexGreat    = "#94cc11"
+	badgeColorHexGood     = "#ccd311"
+	badgeColorHexPassable = "#ccb311"
+	badgeColorHexBad      = "#cc8111"
+	badgeColorHexVeryBad  = "#c7130a"
+)
+
+// UptimeBadge handles the automatic generation of badge based on the group name and endpoint name passed.
+//
+// Valid values for {duration}: 7d, 24h, 1h
+func UptimeBadge(writer http.ResponseWriter, request *http.Request) {
+	variables := mux.Vars(request)
+	duration := variables["duration"]
+	var from time.Time
+	switch duration {
+	case "7d":
+		from = time.Now().Add(-7 * 24 * time.Hour)
+	case "24h":
+		from = time.Now().Add(-24 * time.Hour)
+	case "1h":
+		from = time.Now().Add(-2 * time.Hour) // Because uptime metrics are stored by hour, we have to cheat a little
+	default:
+		http.Error(writer, "Durations supported: 7d, 24h, 1h", http.StatusBadRequest)
+		return
+	}
+	key := variables["key"]
+	uptime, err := store.Get().GetUptimeByKey(key, from, time.Now())
+	if err != nil {
+		if err == common.ErrEndpointNotFound {
+			http.Error(writer, err.Error(), http.StatusNotFound)
+		} else if err == common.ErrInvalidTimeRange {
+			http.Error(writer, err.Error(), http.StatusBadRequest)
+		} else {
+			http.Error(writer, err.Error(), http.StatusInternalServerError)
+		}
+		return
+	}
+	writer.Header().Set("Content-Type", "image/svg+xml")
+	writer.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
+	writer.Header().Set("Expires", "0")
+	writer.WriteHeader(http.StatusOK)
+	_, _ = writer.Write(generateUptimeBadgeSVG(duration, uptime))
+}
+
+// ResponseTimeBadge handles the automatic generation of badge based on the group name and endpoint name passed.
+//
+// Valid values for {duration}: 7d, 24h, 1h
+func ResponseTimeBadge(writer http.ResponseWriter, request *http.Request) {
+	variables := mux.Vars(request)
+	duration := variables["duration"]
+	var from time.Time
+	switch duration {
+	case "7d":
+		from = time.Now().Add(-7 * 24 * time.Hour)
+	case "24h":
+		from = time.Now().Add(-24 * time.Hour)
+	case "1h":
+		from = time.Now().Add(-2 * time.Hour) // Because response time metrics are stored by hour, we have to cheat a little
+	default:
+		http.Error(writer, "Durations supported: 7d, 24h, 1h", http.StatusBadRequest)
+		return
+	}
+	key := variables["key"]
+	averageResponseTime, err := store.Get().GetAverageResponseTimeByKey(key, from, time.Now())
+	if err != nil {
+		if err == common.ErrEndpointNotFound {
+			http.Error(writer, err.Error(), http.StatusNotFound)
+		} else if err == common.ErrInvalidTimeRange {
+			http.Error(writer, err.Error(), http.StatusBadRequest)
+		} else {
+			http.Error(writer, err.Error(), http.StatusInternalServerError)
+		}
+		return
+	}
+	writer.Header().Set("Content-Type", "image/svg+xml")
+	writer.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
+	writer.Header().Set("Expires", "0")
+	writer.WriteHeader(http.StatusOK)
+	_, _ = writer.Write(generateResponseTimeBadgeSVG(duration, averageResponseTime))
+}
+
+func generateUptimeBadgeSVG(duration string, uptime float64) []byte {
+	var labelWidth, valueWidth, valueWidthAdjustment int
+	switch duration {
+	case "7d":
+		labelWidth = 65
+	case "24h":
+		labelWidth = 70
+	case "1h":
+		labelWidth = 65
+	default:
+	}
+	color := getBadgeColorFromUptime(uptime)
+	sanitizedValue := strings.TrimRight(strings.TrimRight(fmt.Sprintf("%.2f", uptime*100), "0"), ".") + "%"
+	if strings.Contains(sanitizedValue, ".") {
+		valueWidthAdjustment = -10
+	}
+	valueWidth = (len(sanitizedValue) * 11) + valueWidthAdjustment
+	width := labelWidth + valueWidth
+	labelX := labelWidth / 2
+	valueX := labelWidth + (valueWidth / 2)
+	svg := []byte(fmt.Sprintf(`<svg xmlns="http://www.w3.org/2000/svg" width="%d" height="20">
+  <linearGradient id="b" x2="0" y2="100%%">
+    <stop offset="0" stop-color="#bbb" stop-opacity=".1"/>
+    <stop offset="1" stop-opacity=".1"/>
+  </linearGradient>
+  <mask id="a">
+    <rect width="%d" height="20" rx="3" fill="#fff"/>
+  </mask>
+  <g mask="url(#a)">
+    <path fill="#555" d="M0 0h%dv20H0z"/>
+    <path fill="%s" d="M%d 0h%dv20H%dz"/>
+    <path fill="url(#b)" d="M0 0h%dv20H0z"/>
+  </g>
+  <g fill="#fff" text-anchor="middle" font-family="DejaVu Sans,Verdana,Geneva,sans-serif" font-size="11">
+    <text x="%d" y="15" fill="#010101" fill-opacity=".3">
+      uptime %s
+    </text>
+    <text x="%d" y="14">
+      uptime %s
+    </text>
+    <text x="%d" y="15" fill="#010101" fill-opacity=".3">
+      %s
+    </text>
+    <text x="%d" y="14">
+      %s
+    </text>
+  </g>
+</svg>`, width, width, labelWidth, color, labelWidth, valueWidth, labelWidth, width, labelX, duration, labelX, duration, valueX, sanitizedValue, valueX, sanitizedValue))
+	return svg
+}
+
+func getBadgeColorFromUptime(uptime float64) string {
+	if uptime >= 0.975 {
+		return badgeColorHexAwesome
+	} else if uptime >= 0.95 {
+		return badgeColorHexGreat
+	} else if uptime >= 0.9 {
+		return badgeColorHexGood
+	} else if uptime >= 0.8 {
+		return badgeColorHexPassable
+	} else if uptime >= 0.65 {
+		return badgeColorHexBad
+	}
+	return badgeColorHexVeryBad
+}
+
+func generateResponseTimeBadgeSVG(duration string, averageResponseTime int) []byte {
+	var labelWidth, valueWidth int
+	switch duration {
+	case "7d":
+		labelWidth = 105
+	case "24h":
+		labelWidth = 110
+	case "1h":
+		labelWidth = 105
+	default:
+	}
+	color := getBadgeColorFromResponseTime(averageResponseTime)
+	sanitizedValue := strconv.Itoa(averageResponseTime) + "ms"
+	valueWidth = len(sanitizedValue) * 11
+	width := labelWidth + valueWidth
+	labelX := labelWidth / 2
+	valueX := labelWidth + (valueWidth / 2)
+	svg := []byte(fmt.Sprintf(`<svg xmlns="http://www.w3.org/2000/svg" width="%d" height="20">
+  <linearGradient id="b" x2="0" y2="100%%">
+    <stop offset="0" stop-color="#bbb" stop-opacity=".1"/>
+    <stop offset="1" stop-opacity=".1"/>
+  </linearGradient>
+  <mask id="a">
+    <rect width="%d" height="20" rx="3" fill="#fff"/>
+  </mask>
+  <g mask="url(#a)">
+    <path fill="#555" d="M0 0h%dv20H0z"/>
+    <path fill="%s" d="M%d 0h%dv20H%dz"/>
+    <path fill="url(#b)" d="M0 0h%dv20H0z"/>
+  </g>
+  <g fill="#fff" text-anchor="middle" font-family="DejaVu Sans,Verdana,Geneva,sans-serif" font-size="11">
+    <text x="%d" y="15" fill="#010101" fill-opacity=".3">
+      response time %s
+    </text>
+    <text x="%d" y="14">
+      response time %s
+    </text>
+    <text x="%d" y="15" fill="#010101" fill-opacity=".3">
+      %s
+    </text>
+    <text x="%d" y="14">
+      %s
+    </text>
+  </g>
+</svg>`, width, width, labelWidth, color, labelWidth, valueWidth, labelWidth, width, labelX, duration, labelX, duration, valueX, sanitizedValue, valueX, sanitizedValue))
+	return svg
+}
+
+func getBadgeColorFromResponseTime(responseTime int) string {
+	if responseTime <= 50 {
+		return badgeColorHexAwesome
+	} else if responseTime <= 200 {
+		return badgeColorHexGreat
+	} else if responseTime <= 300 {
+		return badgeColorHexGood
+	} else if responseTime <= 500 {
+		return badgeColorHexPassable
+	} else if responseTime <= 750 {
+		return badgeColorHexBad
+	}
+	return badgeColorHexVeryBad
+}

controller/handler/badge_test.go

@@ -0,0 +1,231 @@
+package handler
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strconv"
+	"testing"
+	"time"
+
+	"github.com/TwiN/gatus/v3/config"
+	"github.com/TwiN/gatus/v3/core"
+	"github.com/TwiN/gatus/v3/storage/store"
+	"github.com/TwiN/gatus/v3/watchdog"
+)
+
+func TestUptimeBadge(t *testing.T) {
+	defer store.Get().Clear()
+	defer cache.Clear()
+	cfg := &config.Config{
+		Metrics: true,
+		Endpoints: []*core.Endpoint{
+			{
+				Name:  "frontend",
+				Group: "core",
+			},
+			{
+				Name:  "backend",
+				Group: "core",
+			},
+		},
+	}
+	watchdog.UpdateEndpointStatuses(cfg.Endpoints[0], &core.Result{Success: true, Duration: time.Millisecond, Timestamp: time.Now()})
+	watchdog.UpdateEndpointStatuses(cfg.Endpoints[1], &core.Result{Success: false, Duration: time.Second, Timestamp: time.Now()})
+	router := CreateRouter("../../web/static", cfg.Security, nil, cfg.Metrics)
+	type Scenario struct {
+		Name         string
+		Path         string
+		ExpectedCode int
+		Gzip         bool
+	}
+	scenarios := []Scenario{
+		{
+			Name:         "badge-uptime-1h",
+			Path:         "/api/v1/endpoints/core_frontend/uptimes/1h/badge.svg",
+			ExpectedCode: http.StatusOK,
+		},
+		{
+			Name:         "badge-uptime-24h",
+			Path:         "/api/v1/endpoints/core_backend/uptimes/24h/badge.svg",
+			ExpectedCode: http.StatusOK,
+		},
+		{
+			Name:         "badge-uptime-7d",
+			Path:         "/api/v1/endpoints/core_frontend/uptimes/7d/badge.svg",
+			ExpectedCode: http.StatusOK,
+		},
+		{
+			Name:         "badge-uptime-with-invalid-duration",
+			Path:         "/api/v1/endpoints/core_backend/uptimes/3d/badge.svg",
+			ExpectedCode: http.StatusBadRequest,
+		},
+		{
+			Name:         "badge-uptime-for-invalid-key",
+			Path:         "/api/v1/endpoints/invalid_key/uptimes/7d/badge.svg",
+			ExpectedCode: http.StatusNotFound,
+		},
+		{
+			Name:         "badge-response-time-1h",
+			Path:         "/api/v1/endpoints/core_frontend/response-times/1h/badge.svg",
+			ExpectedCode: http.StatusOK,
+		},
+		{
+			Name:         "badge-response-time-24h",
+			Path:         "/api/v1/endpoints/core_backend/response-times/24h/badge.svg",
+			ExpectedCode: http.StatusOK,
+		},
+		{
+			Name:         "badge-response-time-7d",
+			Path:         "/api/v1/endpoints/core_frontend/response-times/7d/badge.svg",
+			ExpectedCode: http.StatusOK,
+		},
+		{
+			Name:         "badge-response-time-with-invalid-duration",
+			Path:         "/api/v1/endpoints/core_backend/response-times/3d/badge.svg",
+			ExpectedCode: http.StatusBadRequest,
+		},
+		{
+			Name:         "badge-response-time-for-invalid-key",
+			Path:         "/api/v1/endpoints/invalid_key/response-times/7d/badge.svg",
+			ExpectedCode: http.StatusNotFound,
+		},
+		{
+			Name:         "chart-response-time-24h",
+			Path:         "/api/v1/endpoints/core_backend/response-times/24h/chart.svg",
+			ExpectedCode: http.StatusOK,
+		},
+		{ // XXX: Remove this in v4.0.0
+			Name:         "backward-compatible-services-badge-uptime-1h",
+			Path:         "/api/v1/services/core_frontend/uptimes/1h/badge.svg",
+			ExpectedCode: http.StatusOK,
+		},
+		{ // XXX: Remove this in v4.0.0
+			Name:         "backward-compatible-services-chart-response-time-24h",
+			Path:         "/api/v1/services/core_backend/response-times/24h/chart.svg",
+			ExpectedCode: http.StatusOK,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			request, _ := http.NewRequest("GET", scenario.Path, http.NoBody)
+			if scenario.Gzip {
+				request.Header.Set("Accept-Encoding", "gzip")
+			}
+			responseRecorder := httptest.NewRecorder()
+			router.ServeHTTP(responseRecorder, request)
+			if responseRecorder.Code != scenario.ExpectedCode {
+				t.Errorf("%s %s should have returned %d, but returned %d instead", request.Method, request.URL, scenario.ExpectedCode, responseRecorder.Code)
+			}
+		})
+	}
+}
+
+func TestGetBadgeColorFromUptime(t *testing.T) {
+	scenarios := []struct {
+		Uptime        float64
+		ExpectedColor string
+	}{
+		{
+			Uptime:        1,
+			ExpectedColor: badgeColorHexAwesome,
+		},
+		{
+			Uptime:        0.99,
+			ExpectedColor: badgeColorHexAwesome,
+		},
+		{
+			Uptime:        0.97,
+			ExpectedColor: badgeColorHexGreat,
+		},
+		{
+			Uptime:        0.95,
+			ExpectedColor: badgeColorHexGreat,
+		},
+		{
+			Uptime:        0.93,
+			ExpectedColor: badgeColorHexGood,
+		},
+		{
+			Uptime:        0.9,
+			ExpectedColor: badgeColorHexGood,
+		},
+		{
+			Uptime:        0.85,
+			ExpectedColor: badgeColorHexPassable,
+		},
+		{
+			Uptime:        0.7,
+			ExpectedColor: badgeColorHexBad,
+		},
+		{
+			Uptime:        0.65,
+			ExpectedColor: badgeColorHexBad,
+		},
+		{
+			Uptime:        0.6,
+			ExpectedColor: badgeColorHexVeryBad,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run("uptime-"+strconv.Itoa(int(scenario.Uptime*100)), func(t *testing.T) {
+			if getBadgeColorFromUptime(scenario.Uptime) != scenario.ExpectedColor {
+				t.Errorf("expected %s from %f, got %v", scenario.ExpectedColor, scenario.Uptime, getBadgeColorFromUptime(scenario.Uptime))
+			}
+		})
+	}
+}
+
+func TestGetBadgeColorFromResponseTime(t *testing.T) {
+	scenarios := []struct {
+		ResponseTime  int
+		ExpectedColor string
+	}{
+		{
+			ResponseTime:  10,
+			ExpectedColor: badgeColorHexAwesome,
+		},
+		{
+			ResponseTime:  50,
+			ExpectedColor: badgeColorHexAwesome,
+		},
+		{
+			ResponseTime:  75,
+			ExpectedColor: badgeColorHexGreat,
+		},
+		{
+			ResponseTime:  150,
+			ExpectedColor: badgeColorHexGreat,
+		},
+		{
+			ResponseTime:  201,
+			ExpectedColor: badgeColorHexGood,
+		},
+		{
+			ResponseTime:  300,
+			ExpectedColor: badgeColorHexGood,
+		},
+		{
+			ResponseTime:  301,
+			ExpectedColor: badgeColorHexPassable,
+		},
+		{
+			ResponseTime:  450,
+			ExpectedColor: badgeColorHexPassable,
+		},
+		{
+			ResponseTime:  700,
+			ExpectedColor: badgeColorHexBad,
+		},
+		{
+			ResponseTime:  1500,
+			ExpectedColor: badgeColorHexVeryBad,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run("response-time-"+strconv.Itoa(scenario.ResponseTime), func(t *testing.T) {
+			if getBadgeColorFromResponseTime(scenario.ResponseTime) != scenario.ExpectedColor {
+				t.Errorf("expected %s from %d, got %v", scenario.ExpectedColor, scenario.ResponseTime, getBadgeColorFromResponseTime(scenario.ResponseTime))
+			}
+		})
+	}
+}

controller/handler/chart.go

@@ -0,0 +1,122 @@
+package handler
+
+import (
+	"log"
+	"math"
+	"net/http"
+	"sort"
+	"time"
+
+	"github.com/TwiN/gatus/v3/storage/store"
+	"github.com/TwiN/gatus/v3/storage/store/common"
+	"github.com/gorilla/mux"
+	"github.com/wcharczuk/go-chart/v2"
+	"github.com/wcharczuk/go-chart/v2/drawing"
+)
+
+const timeFormat = "3:04PM"
+
+var (
+	gridStyle = chart.Style{
+		StrokeColor: drawing.Color{R: 119, G: 119, B: 119, A: 40},
+		StrokeWidth: 1.0,
+	}
+	axisStyle = chart.Style{
+		FontColor: drawing.Color{R: 119, G: 119, B: 119, A: 255},
+	}
+	transparentStyle = chart.Style{
+		FillColor: drawing.Color{R: 255, G: 255, B: 255, A: 0},
+	}
+)
+
+func ResponseTimeChart(writer http.ResponseWriter, r *http.Request) {
+	vars := mux.Vars(r)
+	duration := vars["duration"]
+	var from time.Time
+	switch duration {
+	case "7d":
+		from = time.Now().Truncate(time.Hour).Add(-24 * 7 * time.Hour)
+	case "24h":
+		from = time.Now().Truncate(time.Hour).Add(-24 * time.Hour)
+	default:
+		http.Error(writer, "Durations supported: 7d, 24h", http.StatusBadRequest)
+		return
+	}
+	hourlyAverageResponseTime, err := store.Get().GetHourlyAverageResponseTimeByKey(vars["key"], from, time.Now())
+	if err != nil {
+		if err == common.ErrEndpointNotFound {
+			http.Error(writer, err.Error(), http.StatusNotFound)
+		} else if err == common.ErrInvalidTimeRange {
+			http.Error(writer, err.Error(), http.StatusBadRequest)
+		} else {
+			http.Error(writer, err.Error(), http.StatusInternalServerError)
+		}
+		return
+	}
+	if len(hourlyAverageResponseTime) == 0 {
+		http.Error(writer, "", http.StatusNoContent)
+		return
+	}
+	series := chart.TimeSeries{
+		Name: "Average response time per hour",
+		Style: chart.Style{
+			StrokeWidth: 1.5,
+			DotWidth:    2.0,
+		},
+	}
+	keys := make([]int, 0, len(hourlyAverageResponseTime))
+	earliestTimestamp := int64(0)
+	for hourlyTimestamp := range hourlyAverageResponseTime {
+		keys = append(keys, int(hourlyTimestamp))
+		if earliestTimestamp == 0 || hourlyTimestamp < earliestTimestamp {
+			earliestTimestamp = hourlyTimestamp
+		}
+	}
+	for earliestTimestamp > from.Unix() {
+		earliestTimestamp -= int64(time.Hour.Seconds())
+		keys = append(keys, int(earliestTimestamp))
+	}
+	sort.Ints(keys)
+	var maxAverageResponseTime float64
+	for _, key := range keys {
+		averageResponseTime := float64(hourlyAverageResponseTime[int64(key)])
+		if maxAverageResponseTime < averageResponseTime {
+			maxAverageResponseTime = averageResponseTime
+		}
+		series.XValues = append(series.XValues, time.Unix(int64(key), 0))
+		series.YValues = append(series.YValues, averageResponseTime)
+	}
+	graph := chart.Chart{
+		Canvas:     transparentStyle,
+		Background: transparentStyle,
+		Width:      1280,
+		Height:     300,
+		XAxis: chart.XAxis{
+			ValueFormatter: chart.TimeValueFormatterWithFormat(timeFormat),
+			GridMajorStyle: gridStyle,
+			GridMinorStyle: gridStyle,
+			Style:          axisStyle,
+			NameStyle:      axisStyle,
+		},
+		YAxis: chart.YAxis{
+			Name:           "Average response time",
+			GridMajorStyle: gridStyle,
+			GridMinorStyle: gridStyle,
+			Style:          axisStyle,
+			NameStyle:      axisStyle,
+			Range: &chart.ContinuousRange{
+				Min: 0,
+				Max: math.Ceil(maxAverageResponseTime * 1.25),
+			},
+		},
+		Series: []chart.Series{series},
+	}
+	writer.Header().Set("Content-Type", "image/svg+xml")
+	writer.Header().Set("Cache-Control", "no-cache, no-store")
+	writer.Header().Set("Expires", "0")
+	writer.WriteHeader(http.StatusOK)
+	if err := graph.Render(chart.SVG, writer); err != nil {
+		log.Println("[handler][ResponseTimeChart] Failed to render response time chart:", err.Error())
+		return
+	}
+}

controller/handler/chart_test.go

@@ -0,0 +1,80 @@
+package handler
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/TwiN/gatus/v3/config"
+	"github.com/TwiN/gatus/v3/core"
+	"github.com/TwiN/gatus/v3/storage/store"
+	"github.com/TwiN/gatus/v3/watchdog"
+)
+
+func TestResponseTimeChart(t *testing.T) {
+	defer store.Get().Clear()
+	defer cache.Clear()
+	cfg := &config.Config{
+		Metrics: true,
+		Endpoints: []*core.Endpoint{
+			{
+				Name:  "frontend",
+				Group: "core",
+			},
+			{
+				Name:  "backend",
+				Group: "core",
+			},
+		},
+	}
+	watchdog.UpdateEndpointStatuses(cfg.Endpoints[0], &core.Result{Success: true, Duration: time.Millisecond, Timestamp: time.Now()})
+	watchdog.UpdateEndpointStatuses(cfg.Endpoints[1], &core.Result{Success: false, Duration: time.Second, Timestamp: time.Now()})
+	router := CreateRouter("../../web/static", cfg.Security, nil, cfg.Metrics)
+	type Scenario struct {
+		Name         string
+		Path         string
+		ExpectedCode int
+		Gzip         bool
+	}
+	scenarios := []Scenario{
+		{
+			Name:         "chart-response-time-24h",
+			Path:         "/api/v1/endpoints/core_backend/response-times/24h/chart.svg",
+			ExpectedCode: http.StatusOK,
+		},
+		{
+			Name:         "chart-response-time-7d",
+			Path:         "/api/v1/endpoints/core_frontend/response-times/7d/chart.svg",
+			ExpectedCode: http.StatusOK,
+		},
+		{
+			Name:         "chart-response-time-with-invalid-duration",
+			Path:         "/api/v1/endpoints/core_backend/response-times/3d/chart.svg",
+			ExpectedCode: http.StatusBadRequest,
+		},
+		{
+			Name:         "chart-response-time-for-invalid-key",
+			Path:         "/api/v1/endpoints/invalid_key/response-times/7d/chart.svg",
+			ExpectedCode: http.StatusNotFound,
+		},
+		{ // XXX: Remove this in v4.0.0
+			Name:         "backward-compatible-services-chart-response-time-24h",
+			Path:         "/api/v1/services/core_backend/response-times/24h/chart.svg",
+			ExpectedCode: http.StatusOK,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			request, _ := http.NewRequest("GET", scenario.Path, http.NoBody)
+			if scenario.Gzip {
+				request.Header.Set("Accept-Encoding", "gzip")
+			}
+			responseRecorder := httptest.NewRecorder()
+			router.ServeHTTP(responseRecorder, request)
+			if responseRecorder.Code != scenario.ExpectedCode {
+				t.Errorf("%s %s should have returned %d, but returned %d instead", request.Method, request.URL, scenario.ExpectedCode, responseRecorder.Code)
+			}
+		})
+	}
+}

controller/handler/cors.go

@@ -0,0 +1,10 @@
+package handler
+
+import "net/http"
+
+func DevelopmentCORS(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Access-Control-Allow-Origin", "http://localhost:8081")
+		next.ServeHTTP(w, r)
+	})
+}

controller/handler/endpoint_status.go

@@ -0,0 +1,103 @@
+package handler
+
+import (
+	"bytes"
+	"compress/gzip"
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"strings"
+	"time"
+
+	"github.com/TwiN/gatus/v3/storage/store"
+	"github.com/TwiN/gatus/v3/storage/store/common"
+	"github.com/TwiN/gatus/v3/storage/store/common/paging"
+	"github.com/TwiN/gocache"
+	"github.com/gorilla/mux"
+)
+
+const (
+	cacheTTL = 10 * time.Second
+)
+
+var (
+	cache = gocache.NewCache().WithMaxSize(100).WithEvictionPolicy(gocache.FirstInFirstOut)
+)
+
+// EndpointStatuses handles requests to retrieve all EndpointStatus
+// Due to the size of the response, this function leverages a cache.
+// Must not be wrapped by GzipHandler
+func EndpointStatuses(writer http.ResponseWriter, r *http.Request) {
+	page, pageSize := extractPageAndPageSizeFromRequest(r)
+	gzipped := strings.Contains(r.Header.Get("Accept-Encoding"), "gzip")
+	var exists bool
+	var value interface{}
+	if gzipped {
+		writer.Header().Set("Content-Encoding", "gzip")
+		value, exists = cache.Get(fmt.Sprintf("endpoint-status-%d-%d-gzipped", page, pageSize))
+	} else {
+		value, exists = cache.Get(fmt.Sprintf("endpoint-status-%d-%d", page, pageSize))
+	}
+	var data []byte
+	if !exists {
+		var err error
+		buffer := &bytes.Buffer{}
+		gzipWriter := gzip.NewWriter(buffer)
+		endpointStatuses, err := store.Get().GetAllEndpointStatuses(paging.NewEndpointStatusParams().WithResults(page, pageSize))
+		if err != nil {
+			log.Printf("[handler][EndpointStatuses] Failed to retrieve endpoint statuses: %s", err.Error())
+			http.Error(writer, err.Error(), http.StatusInternalServerError)
+			return
+		}
+		data, err = json.Marshal(endpointStatuses)
+		if err != nil {
+			log.Printf("[handler][EndpointStatuses] Unable to marshal object to JSON: %s", err.Error())
+			http.Error(writer, "unable to marshal object to JSON", http.StatusInternalServerError)
+			return
+		}
+		_, _ = gzipWriter.Write(data)
+		_ = gzipWriter.Close()
+		gzippedData := buffer.Bytes()
+		cache.SetWithTTL(fmt.Sprintf("endpoint-status-%d-%d", page, pageSize), data, cacheTTL)
+		cache.SetWithTTL(fmt.Sprintf("endpoint-status-%d-%d-gzipped", page, pageSize), gzippedData, cacheTTL)
+		if gzipped {
+			data = gzippedData
+		}
+	} else {
+		data = value.([]byte)
+	}
+	writer.Header().Add("Content-Type", "application/json")
+	writer.WriteHeader(http.StatusOK)
+	_, _ = writer.Write(data)
+}
+
+// EndpointStatus retrieves a single core.EndpointStatus by group and endpoint name
+func EndpointStatus(writer http.ResponseWriter, r *http.Request) {
+	page, pageSize := extractPageAndPageSizeFromRequest(r)
+	vars := mux.Vars(r)
+	endpointStatus, err := store.Get().GetEndpointStatusByKey(vars["key"], paging.NewEndpointStatusParams().WithResults(page, pageSize).WithEvents(1, common.MaximumNumberOfEvents))
+	if err != nil {
+		if err == common.ErrEndpointNotFound {
+			http.Error(writer, err.Error(), http.StatusNotFound)
+			return
+		}
+		log.Printf("[handler][EndpointStatus] Failed to retrieve endpoint status: %s", err.Error())
+		http.Error(writer, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	if endpointStatus == nil {
+		log.Printf("[handler][EndpointStatus] Endpoint with key=%s not found", vars["key"])
+		http.Error(writer, "not found", http.StatusNotFound)
+		return
+	}
+	output, err := json.Marshal(endpointStatus)
+	if err != nil {
+		log.Printf("[handler][EndpointStatus] Unable to marshal object to JSON: %s", err.Error())
+		http.Error(writer, "unable to marshal object to JSON", http.StatusInternalServerError)
+		return
+	}
+	writer.Header().Add("Content-Type", "application/json")
+	writer.WriteHeader(http.StatusOK)
+	_, _ = writer.Write(output)
+}

controller/handler/endpoint_status_test.go

@@ -0,0 +1,226 @@
+package handler
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/TwiN/gatus/v3/config"
+	"github.com/TwiN/gatus/v3/core"
+	"github.com/TwiN/gatus/v3/storage/store"
+	"github.com/TwiN/gatus/v3/watchdog"
+)
+
+var (
+	firstCondition  = core.Condition("[STATUS] == 200")
+	secondCondition = core.Condition("[RESPONSE_TIME] < 500")
+	thirdCondition  = core.Condition("[CERTIFICATE_EXPIRATION] < 72h")
+
+	timestamp = time.Now()
+
+	testEndpoint = core.Endpoint{
+		Name:                    "name",
+		Group:                   "group",
+		URL:                     "https://example.org/what/ever",
+		Method:                  "GET",
+		Body:                    "body",
+		Interval:                30 * time.Second,
+		Conditions:              []*core.Condition{&firstCondition, &secondCondition, &thirdCondition},
+		Alerts:                  nil,
+		NumberOfFailuresInARow:  0,
+		NumberOfSuccessesInARow: 0,
+	}
+	testSuccessfulResult = core.Result{
+		Hostname:              "example.org",
+		IP:                    "127.0.0.1",
+		HTTPStatus:            200,
+		Errors:                nil,
+		Connected:             true,
+		Success:               true,
+		Timestamp:             timestamp,
+		Duration:              150 * time.Millisecond,
+		CertificateExpiration: 10 * time.Hour,
+		ConditionResults: []*core.ConditionResult{
+			{
+				Condition: "[STATUS] == 200",
+				Success:   true,
+			},
+			{
+				Condition: "[RESPONSE_TIME] < 500",
+				Success:   true,
+			},
+			{
+				Condition: "[CERTIFICATE_EXPIRATION] < 72h",
+				Success:   true,
+			},
+		},
+	}
+	testUnsuccessfulResult = core.Result{
+		Hostname:              "example.org",
+		IP:                    "127.0.0.1",
+		HTTPStatus:            200,
+		Errors:                []string{"error-1", "error-2"},
+		Connected:             true,
+		Success:               false,
+		Timestamp:             timestamp,
+		Duration:              750 * time.Millisecond,
+		CertificateExpiration: 10 * time.Hour,
+		ConditionResults: []*core.ConditionResult{
+			{
+				Condition: "[STATUS] == 200",
+				Success:   true,
+			},
+			{
+				Condition: "[RESPONSE_TIME] < 500",
+				Success:   false,
+			},
+			{
+				Condition: "[CERTIFICATE_EXPIRATION] < 72h",
+				Success:   false,
+			},
+		},
+	}
+)
+
+func TestEndpointStatus(t *testing.T) {
+	defer store.Get().Clear()
+	defer cache.Clear()
+	cfg := &config.Config{
+		Metrics: true,
+		Endpoints: []*core.Endpoint{
+			{
+				Name:  "frontend",
+				Group: "core",
+			},
+			{
+				Name:  "backend",
+				Group: "core",
+			},
+		},
+	}
+	watchdog.UpdateEndpointStatuses(cfg.Endpoints[0], &core.Result{Success: true, Duration: time.Millisecond, Timestamp: time.Now()})
+	watchdog.UpdateEndpointStatuses(cfg.Endpoints[1], &core.Result{Success: false, Duration: time.Second, Timestamp: time.Now()})
+	router := CreateRouter("../../web/static", cfg.Security, nil, cfg.Metrics)
+
+	type Scenario struct {
+		Name         string
+		Path         string
+		ExpectedCode int
+		Gzip         bool
+	}
+	scenarios := []Scenario{
+		{
+			Name:         "endpoint-status",
+			Path:         "/api/v1/endpoints/core_frontend/statuses",
+			ExpectedCode: http.StatusOK,
+		},
+		{
+			Name:         "endpoint-status-gzip",
+			Path:         "/api/v1/endpoints/core_frontend/statuses",
+			ExpectedCode: http.StatusOK,
+			Gzip:         true,
+		},
+		{
+			Name:         "endpoint-status-pagination",
+			Path:         "/api/v1/endpoints/core_frontend/statuses?page=1&pageSize=20",
+			ExpectedCode: http.StatusOK,
+		},
+		{
+			Name:         "endpoint-status-for-invalid-key",
+			Path:         "/api/v1/endpoints/invalid_key/statuses",
+			ExpectedCode: http.StatusNotFound,
+		},
+		{ // XXX: Remove this in v4.0.0
+			Name:         "backward-compatible-service-status",
+			Path:         "/api/v1/services/core_frontend/statuses",
+			ExpectedCode: http.StatusOK,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			request, _ := http.NewRequest("GET", scenario.Path, http.NoBody)
+			if scenario.Gzip {
+				request.Header.Set("Accept-Encoding", "gzip")
+			}
+			responseRecorder := httptest.NewRecorder()
+			router.ServeHTTP(responseRecorder, request)
+			if responseRecorder.Code != scenario.ExpectedCode {
+				t.Errorf("%s %s should have returned %d, but returned %d instead", request.Method, request.URL, scenario.ExpectedCode, responseRecorder.Code)
+			}
+		})
+	}
+}
+
+func TestEndpointStatuses(t *testing.T) {
+	defer store.Get().Clear()
+	defer cache.Clear()
+	firstResult := &testSuccessfulResult
+	secondResult := &testUnsuccessfulResult
+	store.Get().Insert(&testEndpoint, firstResult)
+	store.Get().Insert(&testEndpoint, secondResult)
+	// Can't be bothered dealing with timezone issues on the worker that runs the automated tests
+	firstResult.Timestamp = time.Time{}
+	secondResult.Timestamp = time.Time{}
+	router := CreateRouter("../../web/static", nil, nil, false)
+
+	type Scenario struct {
+		Name         string
+		Path         string
+		ExpectedCode int
+		ExpectedBody string
+	}
+	scenarios := []Scenario{
+		{
+			Name:         "no-pagination",
+			Path:         "/api/v1/endpoints/statuses",
+			ExpectedCode: http.StatusOK,
+			ExpectedBody: `[{"name":"name","group":"group","key":"group_name","results":[{"status":200,"hostname":"example.org","duration":150000000,"conditionResults":[{"condition":"[STATUS] == 200","success":true},{"condition":"[RESPONSE_TIME] \u003c 500","success":true},{"condition":"[CERTIFICATE_EXPIRATION] \u003c 72h","success":true}],"success":true,"timestamp":"0001-01-01T00:00:00Z"},{"status":200,"hostname":"example.org","duration":750000000,"errors":["error-1","error-2"],"conditionResults":[{"condition":"[STATUS] == 200","success":true},{"condition":"[RESPONSE_TIME] \u003c 500","success":false},{"condition":"[CERTIFICATE_EXPIRATION] \u003c 72h","success":false}],"success":false,"timestamp":"0001-01-01T00:00:00Z"}]}]`,
+		},
+		{
+			Name:         "pagination-first-result",
+			Path:         "/api/v1/endpoints/statuses?page=1&pageSize=1",
+			ExpectedCode: http.StatusOK,
+			ExpectedBody: `[{"name":"name","group":"group","key":"group_name","results":[{"status":200,"hostname":"example.org","duration":750000000,"errors":["error-1","error-2"],"conditionResults":[{"condition":"[STATUS] == 200","success":true},{"condition":"[RESPONSE_TIME] \u003c 500","success":false},{"condition":"[CERTIFICATE_EXPIRATION] \u003c 72h","success":false}],"success":false,"timestamp":"0001-01-01T00:00:00Z"}]}]`,
+		},
+		{
+			Name:         "pagination-second-result",
+			Path:         "/api/v1/endpoints/statuses?page=2&pageSize=1",
+			ExpectedCode: http.StatusOK,
+			ExpectedBody: `[{"name":"name","group":"group","key":"group_name","results":[{"status":200,"hostname":"example.org","duration":150000000,"conditionResults":[{"condition":"[STATUS] == 200","success":true},{"condition":"[RESPONSE_TIME] \u003c 500","success":true},{"condition":"[CERTIFICATE_EXPIRATION] \u003c 72h","success":true}],"success":true,"timestamp":"0001-01-01T00:00:00Z"}]}]`,
+		},
+		{
+			Name:         "pagination-no-results",
+			Path:         "/api/v1/endpoints/statuses?page=5&pageSize=20",
+			ExpectedCode: http.StatusOK,
+			ExpectedBody: `[{"name":"name","group":"group","key":"group_name","results":[]}]`,
+		},
+		{
+			Name:         "invalid-pagination-should-fall-back-to-default",
+			Path:         "/api/v1/endpoints/statuses?page=INVALID&pageSize=INVALID",
+			ExpectedCode: http.StatusOK,
+			ExpectedBody: `[{"name":"name","group":"group","key":"group_name","results":[{"status":200,"hostname":"example.org","duration":150000000,"conditionResults":[{"condition":"[STATUS] == 200","success":true},{"condition":"[RESPONSE_TIME] \u003c 500","success":true},{"condition":"[CERTIFICATE_EXPIRATION] \u003c 72h","success":true}],"success":true,"timestamp":"0001-01-01T00:00:00Z"},{"status":200,"hostname":"example.org","duration":750000000,"errors":["error-1","error-2"],"conditionResults":[{"condition":"[STATUS] == 200","success":true},{"condition":"[RESPONSE_TIME] \u003c 500","success":false},{"condition":"[CERTIFICATE_EXPIRATION] \u003c 72h","success":false}],"success":false,"timestamp":"0001-01-01T00:00:00Z"}]}]`,
+		},
+		{ // XXX: Remove this in v4.0.0
+			Name:         "backward-compatible-service-status",
+			Path:         "/api/v1/services/statuses",
+			ExpectedCode: http.StatusOK,
+			ExpectedBody: `[{"name":"name","group":"group","key":"group_name","results":[{"status":200,"hostname":"example.org","duration":150000000,"conditionResults":[{"condition":"[STATUS] == 200","success":true},{"condition":"[RESPONSE_TIME] \u003c 500","success":true},{"condition":"[CERTIFICATE_EXPIRATION] \u003c 72h","success":true}],"success":true,"timestamp":"0001-01-01T00:00:00Z"},{"status":200,"hostname":"example.org","duration":750000000,"errors":["error-1","error-2"],"conditionResults":[{"condition":"[STATUS] == 200","success":true},{"condition":"[RESPONSE_TIME] \u003c 500","success":false},{"condition":"[CERTIFICATE_EXPIRATION] \u003c 72h","success":false}],"success":false,"timestamp":"0001-01-01T00:00:00Z"}]}]`,
+		},
+	}
+
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			request, _ := http.NewRequest("GET", scenario.Path, http.NoBody)
+			responseRecorder := httptest.NewRecorder()
+			router.ServeHTTP(responseRecorder, request)
+			if responseRecorder.Code != scenario.ExpectedCode {
+				t.Errorf("%s %s should have returned %d, but returned %d instead", request.Method, request.URL, scenario.ExpectedCode, responseRecorder.Code)
+			}
+			output := responseRecorder.Body.String()
+			if output != scenario.ExpectedBody {
+				t.Errorf("expected:\n %s\n\ngot:\n %s", scenario.ExpectedBody, output)
+			}
+		})
+	}
+}

controller/handler/favicon.go

@@ -0,0 +1,12 @@
+package handler
+
+import (
+	"net/http"
+)
+
+// FavIcon handles requests for /favicon.ico
+func FavIcon(staticFolder string) http.HandlerFunc {
+	return func(writer http.ResponseWriter, request *http.Request) {
+		http.ServeFile(writer, request, staticFolder+"/favicon.ico")
+	}
+}

controller/handler/favicon_test.go

@@ -0,0 +1,33 @@
+package handler
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestFavIcon(t *testing.T) {
+	router := CreateRouter("../../web/static", nil, nil, false)
+	type Scenario struct {
+		Name         string
+		Path         string
+		ExpectedCode int
+	}
+	scenarios := []Scenario{
+		{
+			Name:         "favicon",
+			Path:         "/favicon.ico",
+			ExpectedCode: http.StatusOK,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			request, _ := http.NewRequest("GET", scenario.Path, http.NoBody)
+			responseRecorder := httptest.NewRecorder()
+			router.ServeHTTP(responseRecorder, request)
+			if responseRecorder.Code != scenario.ExpectedCode {
+				t.Errorf("%s %s should have returned %d, but returned %d instead", request.Method, request.URL, scenario.ExpectedCode, responseRecorder.Code)
+			}
+		})
+	}
+}

controller/handler/gzip.go

@@ -0,0 +1,59 @@
+package handler
+
+import (
+	"compress/gzip"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"strings"
+	"sync"
+)
+
+var gzPool = sync.Pool{
+	New: func() interface{} {
+		return gzip.NewWriter(ioutil.Discard)
+	},
+}
+
+type gzipResponseWriter struct {
+	io.Writer
+	http.ResponseWriter
+}
+
+// WriteHeader sends an HTTP response header with the provided status code.
+// It also deletes the Content-Length header, since the GZIP compression may modify the size of the payload
+func (w *gzipResponseWriter) WriteHeader(status int) {
+	w.Header().Del("Content-Length")
+	w.ResponseWriter.WriteHeader(status)
+}
+
+// Write writes len(b) bytes from b to the underlying data stream.
+func (w *gzipResponseWriter) Write(b []byte) (int, error) {
+	return w.Writer.Write(b)
+}
+
+// GzipHandler compresses the response of a given http.Handler if the request's headers specify that the client
+// supports gzip encoding
+func GzipHandler(next http.Handler) http.Handler {
+	return GzipHandlerFunc(func(writer http.ResponseWriter, r *http.Request) {
+		next.ServeHTTP(writer, r)
+	})
+}
+
+// GzipHandlerFunc compresses the response of a given http.HandlerFunc if the request's headers specify that the client
+// supports gzip encoding
+func GzipHandlerFunc(next http.HandlerFunc) http.HandlerFunc {
+	return func(writer http.ResponseWriter, r *http.Request) {
+		// If the request doesn't specify that it supports gzip, then don't compress it
+		if !strings.Contains(r.Header.Get("Accept-Encoding"), "gzip") {
+			next.ServeHTTP(writer, r)
+			return
+		}
+		writer.Header().Set("Content-Encoding", "gzip")
+		gz := gzPool.Get().(*gzip.Writer)
+		defer gzPool.Put(gz)
+		gz.Reset(writer)
+		defer gz.Close()
+		next.ServeHTTP(&gzipResponseWriter{ResponseWriter: writer, Writer: gz}, r)
+	}
+}

controller/handler/handler.go

@@ -0,0 +1,47 @@
+package handler
+
+import (
+	"net/http"
+
+	"github.com/TwiN/gatus/v3/config/ui"
+	"github.com/TwiN/gatus/v3/security"
+	"github.com/TwiN/health"
+	"github.com/gorilla/mux"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+func CreateRouter(staticFolder string, securityConfig *security.Config, uiConfig *ui.Config, enabledMetrics bool) *mux.Router {
+	router := mux.NewRouter()
+	if enabledMetrics {
+		router.Handle("/metrics", promhttp.Handler()).Methods("GET")
+	}
+	router.Handle("/health", health.Handler().WithJSON(true)).Methods("GET")
+	router.HandleFunc("/favicon.ico", FavIcon(staticFolder)).Methods("GET")
+	// Endpoints
+	router.HandleFunc("/api/v1/endpoints/statuses", secureIfNecessary(securityConfig, EndpointStatuses)).Methods("GET") // No GzipHandler for this one, because we cache the content as Gzipped already
+	router.HandleFunc("/api/v1/endpoints/{key}/statuses", secureIfNecessary(securityConfig, GzipHandlerFunc(EndpointStatus))).Methods("GET")
+	router.HandleFunc("/api/v1/endpoints/{key}/uptimes/{duration}/badge.svg", UptimeBadge).Methods("GET")
+	router.HandleFunc("/api/v1/endpoints/{key}/response-times/{duration}/badge.svg", ResponseTimeBadge).Methods("GET")
+	router.HandleFunc("/api/v1/endpoints/{key}/response-times/{duration}/chart.svg", ResponseTimeChart).Methods("GET")
+	// XXX: Remove the lines between this and the next XXX comment in v4.0.0
+	router.HandleFunc("/api/v1/services/statuses", secureIfNecessary(securityConfig, EndpointStatuses)).Methods("GET") // No GzipHandler for this one, because we cache the content as Gzipped already
+	router.HandleFunc("/api/v1/services/{key}/statuses", secureIfNecessary(securityConfig, GzipHandlerFunc(EndpointStatus))).Methods("GET")
+	router.HandleFunc("/api/v1/services/{key}/uptimes/{duration}/badge.svg", UptimeBadge).Methods("GET")
+	router.HandleFunc("/api/v1/services/{key}/response-times/{duration}/badge.svg", ResponseTimeBadge).Methods("GET")
+	router.HandleFunc("/api/v1/services/{key}/response-times/{duration}/chart.svg", ResponseTimeChart).Methods("GET")
+	// XXX: Remove the lines between this and the previous XXX comment in v4.0.0
+	// SPA
+	router.HandleFunc("/services/{name}", SinglePageApplication(staticFolder, uiConfig)).Methods("GET") // XXX: Remove this in v4.0.0
+	router.HandleFunc("/endpoints/{name}", SinglePageApplication(staticFolder, uiConfig)).Methods("GET")
+	router.HandleFunc("/", SinglePageApplication(staticFolder, uiConfig)).Methods("GET")
+	// Everything else falls back on static content
+	router.PathPrefix("/").Handler(GzipHandler(http.FileServer(http.Dir(staticFolder))))
+	return router
+}
+
+func secureIfNecessary(securityConfig *security.Config, handler http.HandlerFunc) http.HandlerFunc {
+	if securityConfig != nil && securityConfig.IsValid() {
+		return security.Handler(handler, securityConfig)
+	}
+	return handler
+}

controller/handler/handler_test.go

@@ -0,0 +1,58 @@
+package handler
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestCreateRouter(t *testing.T) {
+	router := CreateRouter("../../web/static", nil, nil, true)
+	type Scenario struct {
+		Name         string
+		Path         string
+		ExpectedCode int
+		Gzip         bool
+	}
+	scenarios := []Scenario{
+		{
+			Name:         "health",
+			Path:         "/health",
+			ExpectedCode: http.StatusOK,
+		},
+		{
+			Name:         "metrics",
+			Path:         "/metrics",
+			ExpectedCode: http.StatusOK,
+		},
+		{
+			Name:         "scripts",
+			Path:         "/js/app.js",
+			ExpectedCode: http.StatusOK,
+		},
+		{
+			Name:         "scripts-gzipped",
+			Path:         "/js/app.js",
+			ExpectedCode: http.StatusOK,
+			Gzip:         true,
+		},
+		{
+			Name:         "index-redirect",
+			Path:         "/index.html",
+			ExpectedCode: http.StatusMovedPermanently,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			request, _ := http.NewRequest("GET", scenario.Path, http.NoBody)
+			if scenario.Gzip {
+				request.Header.Set("Accept-Encoding", "gzip")
+			}
+			responseRecorder := httptest.NewRecorder()
+			router.ServeHTTP(responseRecorder, request)
+			if responseRecorder.Code != scenario.ExpectedCode {
+				t.Errorf("%s %s should have returned %d, but returned %d instead", request.Method, request.URL, scenario.ExpectedCode, responseRecorder.Code)
+			}
+		})
+	}
+}

controller/handler/spa.go

@@ -0,0 +1,27 @@
+package handler
+
+import (
+	"html/template"
+	"log"
+	"net/http"
+
+	"github.com/TwiN/gatus/v3/config/ui"
+)
+
+func SinglePageApplication(staticFolder string, ui *ui.Config) http.HandlerFunc {
+	return func(writer http.ResponseWriter, request *http.Request) {
+		t, err := template.ParseFiles(staticFolder + "/index.html")
+		if err != nil {
+			log.Println("[handler][SinglePageApplication] Failed to parse template:", err.Error())
+			http.ServeFile(writer, request, staticFolder+"/index.html")
+			return
+		}
+		writer.Header().Set("Content-Type", "text/html")
+		err = t.Execute(writer, ui)
+		if err != nil {
+			log.Println("[handler][SinglePageApplication] Failed to parse template:", err.Error())
+			http.ServeFile(writer, request, staticFolder+"/index.html")
+			return
+		}
+	}
+}

controller/handler/spa_test.go

@@ -0,0 +1,70 @@
+package handler
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/TwiN/gatus/v3/config"
+	"github.com/TwiN/gatus/v3/core"
+	"github.com/TwiN/gatus/v3/storage/store"
+	"github.com/TwiN/gatus/v3/watchdog"
+)
+
+func TestSinglePageApplication(t *testing.T) {
+	defer store.Get().Clear()
+	defer cache.Clear()
+	cfg := &config.Config{
+		Metrics: true,
+		Endpoints: []*core.Endpoint{
+			{
+				Name:  "frontend",
+				Group: "core",
+			},
+			{
+				Name:  "backend",
+				Group: "core",
+			},
+		},
+	}
+	watchdog.UpdateEndpointStatuses(cfg.Endpoints[0], &core.Result{Success: true, Duration: time.Millisecond, Timestamp: time.Now()})
+	watchdog.UpdateEndpointStatuses(cfg.Endpoints[1], &core.Result{Success: false, Duration: time.Second, Timestamp: time.Now()})
+	router := CreateRouter("../../web/static", cfg.Security, nil, cfg.Metrics)
+	type Scenario struct {
+		Name         string
+		Path         string
+		ExpectedCode int
+		Gzip         bool
+	}
+	scenarios := []Scenario{
+		{
+			Name:         "frontend-home",
+			Path:         "/",
+			ExpectedCode: http.StatusOK,
+		},
+		{
+			Name:         "frontend-endpoint",
+			Path:         "/endpoints/core_frontend",
+			ExpectedCode: http.StatusOK,
+		},
+		{ // XXX: Remove this in v4.0.0
+			Name:         "frontend-service",
+			Path:         "/services/core_frontend",
+			ExpectedCode: http.StatusOK,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			request, _ := http.NewRequest("GET", scenario.Path, http.NoBody)
+			if scenario.Gzip {
+				request.Header.Set("Accept-Encoding", "gzip")
+			}
+			responseRecorder := httptest.NewRecorder()
+			router.ServeHTTP(responseRecorder, request)
+			if responseRecorder.Code != scenario.ExpectedCode {
+				t.Errorf("%s %s should have returned %d, but returned %d instead", request.Method, request.URL, scenario.ExpectedCode, responseRecorder.Code)
+			}
+		})
+	}
+}