feat(external-endpoint): Implement heartbeat (#1173)

Fixes #741

config/endpoint/external_endpoint.go

@@ -2,13 +2,19 @@ package endpoint
 
 import (
 	"errors"
+	"time"
 
 	"github.com/TwiN/gatus/v5/alerting/alert"
+	"github.com/TwiN/gatus/v5/config/endpoint/heartbeat"
+	"github.com/TwiN/gatus/v5/config/maintenance"
 )
 
 var (
 	// ErrExternalEndpointWithNoToken is the error with which Gatus will panic if an external endpoint is configured without a token.
 	ErrExternalEndpointWithNoToken = errors.New("you must specify a token for each external endpoint")
+
+	// ErrExternalEndpointHeartbeatIntervalTooLow is the error with which Gatus will panic if an external endpoint's heartbeat interval is less than 10 seconds.
+	ErrExternalEndpointHeartbeatIntervalTooLow = errors.New("heartbeat interval must be at least 10 seconds")
 )
 
 // ExternalEndpoint is an endpoint whose result is pushed from outside Gatus, which means that
@@ -30,6 +36,12 @@ type ExternalEndpoint struct {
 	// Alerts is the alerting configuration for the endpoint in case of failure
 	Alerts []*alert.Alert `yaml:"alerts,omitempty"`
 
+	// MaintenanceWindow is the configuration for per-endpoint maintenance windows
+	MaintenanceWindows []*maintenance.Config `yaml:"maintenance-windows,omitempty"`
+
+	// Heartbeat is the configuration that checks if the external endpoint has received new results when it should have.
+	Heartbeat heartbeat.Config `yaml:"heartbeat,omitempty"`
+
 	// NumberOfFailuresInARow is the number of unsuccessful evaluations in a row
 	NumberOfFailuresInARow int `yaml:"-"`
 
@@ -45,6 +57,10 @@ func (externalEndpoint *ExternalEndpoint) ValidateAndSetDefaults() error {
 	if len(externalEndpoint.Token) == 0 {
 		return ErrExternalEndpointWithNoToken
 	}
+	if externalEndpoint.Heartbeat.Interval != 0 && externalEndpoint.Heartbeat.Interval < 10*time.Second {
+		// If the heartbeat interval is set (non-0), it must be at least 10 seconds.
+		return ErrExternalEndpointHeartbeatIntervalTooLow
+	}
 	return nil
 }
 

config/endpoint/heartbeat/heartbeat.go

@@ -0,0 +1,11 @@
+package heartbeat
+
+import "time"
+
+// Config used to check if the external endpoint has received new results when it should have.
+// This configuration is used to trigger alerts when an external endpoint has no new results for a defined period of time
+type Config struct {
+	// Interval is the time interval at which Gatus verifies whether the external endpoint has received new results
+	// If no new result is received within the interval, the endpoint is marked as failed and alerts are triggered
+	Interval time.Duration `yaml:"interval"`
+}