feat: Implement push-based external endpoints (#724)

* refactor: Move SSH outside of endpoint.go
* refactor: Use pointers for Alert receivers
* feat: Implement push-based external endpoints
* Fix failing tests
* Validate external endpoints on start
* Add tests for external endpoints
* refactor some error equality checks
* Improve docs and refactor some code
* Fix UI-related issues with external endpoints

config/config.go

@@ -67,15 +67,18 @@ type Config struct {
 	// Disabling this may lead to inaccurate response times
 	DisableMonitoringLock bool `yaml:"disable-monitoring-lock,omitempty"`
 
-	// Security Configuration for securing access to Gatus
+	// Security is the configuration for securing access to Gatus
 	Security *security.Config `yaml:"security,omitempty"`
 
-	// Alerting Configuration for alerting
+	// Alerting is the configuration for alerting providers
 	Alerting *alerting.Config `yaml:"alerting,omitempty"`
 
-	// Endpoints List of endpoints to monitor
+	// Endpoints is the list of endpoints to monitor
 	Endpoints []*core.Endpoint `yaml:"endpoints,omitempty"`
 
+	// ExternalEndpoints is the list of all external endpoints
+	ExternalEndpoints []*core.ExternalEndpoint `yaml:"external-endpoints,omitempty"`
+
 	// Storage is the configuration for how the data is stored
 	Storage *storage.Config `yaml:"storage,omitempty"`
 
@@ -100,7 +103,6 @@ type Config struct {
 }
 
 func (config *Config) GetEndpointByKey(key string) *core.Endpoint {
-	// TODO: Should probably add a mutex here to prevent concurrent access
 	for i := 0; i < len(config.Endpoints); i++ {
 		ep := config.Endpoints[i]
 		if util.ConvertGroupAndEndpointNameToKey(ep.Group, ep.Name) == key {
@@ -110,9 +112,19 @@ func (config *Config) GetEndpointByKey(key string) *core.Endpoint {
 	return nil
 }
 
+func (config *Config) GetExternalEndpointByKey(key string) *core.ExternalEndpoint {
+	for i := 0; i < len(config.ExternalEndpoints); i++ {
+		ee := config.ExternalEndpoints[i]
+		if util.ConvertGroupAndEndpointNameToKey(ee.Group, ee.Name) == key {
+			return ee
+		}
+	}
+	return nil
+}
+
 // HasLoadedConfigurationBeenModified returns whether one of the file that the
 // configuration has been loaded from has been modified since it was last read
-func (config Config) HasLoadedConfigurationBeenModified() bool {
+func (config *Config) HasLoadedConfigurationBeenModified() bool {
 	lastMod := config.lastFileModTime.Unix()
 	fileInfo, err := os.Stat(config.configPath)
 	if err != nil {
@@ -125,7 +137,7 @@ func (config Config) HasLoadedConfigurationBeenModified() bool {
 			}
 			return nil
 		})
-		return err == errEarlyReturn
+		return errors.Is(err, errEarlyReturn)
 	}
 	return !fileInfo.ModTime().IsZero() && config.lastFileModTime.Unix() < fileInfo.ModTime().Unix()
 }
@@ -135,7 +147,7 @@ func (config *Config) UpdateLastFileModTime() {
 	config.lastFileModTime = time.Now()
 }
 
-// LoadConfiguration loads the full configuration composed from the main configuration file
+// LoadConfiguration loads the full configuration composed of the main configuration file
 // and all composed configuration files
 func LoadConfiguration(configPath string) (*Config, error) {
 	var configBytes []byte
@@ -241,6 +253,9 @@ func parseAndValidateConfigBytes(yamlBytes []byte) (config *Config, err error) {
 		if err := validateEndpointsConfig(config); err != nil {
 			return nil, err
 		}
+		if err := validateExternalEndpointsConfig(config); err != nil {
+			return nil, err
+		}
 		if err := validateWebConfig(config); err != nil {
 			return nil, err
 		}
@@ -336,6 +351,19 @@ func validateEndpointsConfig(config *Config) error {
 	return nil
 }
 
+func validateExternalEndpointsConfig(config *Config) error {
+	for _, externalEndpoint := range config.ExternalEndpoints {
+		if config.Debug {
+			log.Printf("[config.validateExternalEndpointsConfig] Validating external endpoint '%s'", externalEndpoint.Name)
+		}
+		if err := externalEndpoint.ValidateAndSetDefaults(); err != nil {
+			return fmt.Errorf("invalid external endpoint %s: %w", externalEndpoint.DisplayName(), err)
+		}
+	}
+	log.Printf("[config.validateExternalEndpointsConfig] Validated %d external endpoints", len(config.ExternalEndpoints))
+	return nil
+}
+
 func validateSecurityConfig(config *Config) error {
 	if config.Security != nil {
 		if config.Security.IsValid() {

config/config_test.go

@@ -304,11 +304,13 @@ func TestParseAndValidateConfigBytes(t *testing.T) {
 storage:
   type: sqlite
   path: %s
+
 maintenance:
   enabled: true
   start: 00:00
   duration: 4h
   every: [Monday, Thursday]
+
 ui:
   title: T
   header: H
@@ -318,6 +320,16 @@ ui:
       link: "https://example.org"
     - name: "Status page"
       link: "https://status.example.org"
+
+external-endpoints:
+  - name: ext-ep-test
+    group: core
+    token: "potato"
+    alerts:
+      - type: discord
+        description: "healthcheck failed"
+        send-on-resolved: true
+
 endpoints:
   - name: website
     url: https://twin.sh/health
@@ -358,10 +370,33 @@ endpoints:
 	if mc := config.Maintenance; mc == nil || mc.Start != "00:00" || !mc.IsEnabled() || mc.Duration != 4*time.Hour || len(mc.Every) != 2 {
 		t.Error("Expected Config.Maintenance to be configured properly")
 	}
+	if len(config.ExternalEndpoints) != 1 {
+		t.Error("Should have returned one external endpoint")
+	}
+	if config.ExternalEndpoints[0].Name != "ext-ep-test" {
+		t.Errorf("Name should have been %s", "ext-ep-test")
+	}
+	if config.ExternalEndpoints[0].Group != "core" {
+		t.Errorf("Group should have been %s", "core")
+	}
+	if config.ExternalEndpoints[0].Token != "potato" {
+		t.Errorf("Token should have been %s", "potato")
+	}
+	if len(config.ExternalEndpoints[0].Alerts) != 1 {
+		t.Error("Should have returned one alert")
+	}
+	if config.ExternalEndpoints[0].Alerts[0].Type != alert.TypeDiscord {
+		t.Errorf("Type should have been %s", alert.TypeDiscord)
+	}
+	if config.ExternalEndpoints[0].Alerts[0].FailureThreshold != 3 {
+		t.Errorf("FailureThreshold should have been %d, got %d", 3, config.ExternalEndpoints[0].Alerts[0].FailureThreshold)
+	}
+	if config.ExternalEndpoints[0].Alerts[0].SuccessThreshold != 2 {
+		t.Errorf("SuccessThreshold should have been %d, got %d", 2, config.ExternalEndpoints[0].Alerts[0].SuccessThreshold)
+	}
 	if len(config.Endpoints) != 3 {
 		t.Error("Should have returned two endpoints")
 	}
-
 	if config.Endpoints[0].URL != "https://twin.sh/health" {
 		t.Errorf("URL should have been %s", "https://twin.sh/health")
 	}
@@ -383,7 +418,6 @@ endpoints:
 	if len(config.Endpoints[0].Conditions) != 1 {
 		t.Errorf("There should have been %d conditions", 1)
 	}
-
 	if config.Endpoints[1].URL != "https://api.github.com/healthz" {
 		t.Errorf("URL should have been %s", "https://api.github.com/healthz")
 	}