Alerting: Send external URL to the remote Alertmanager (#89701)

* Alerting: Send external URL to the remote Alertmanager

* test that the URL is sent to the remote Alertmanager

* AppURL -> ExternalURL

pkg/services/ngalert/ngalert.go

@@ -203,6 +203,7 @@ func (ng *AlertNG) init() error {
 						URL:               ng.Cfg.UnifiedAlerting.RemoteAlertmanager.URL,
 						PromoteConfig:     true,
 						SyncInterval:      ng.Cfg.UnifiedAlerting.RemoteAlertmanager.SyncInterval,
+						ExternalURL:       ng.Cfg.AppURL,
 					}
 					remoteAM, err := createRemoteAlertmanager(cfg, ng.KVStore, ng.SecretsService.Decrypt, autogenFn, m, ng.tracer)
 					if err != nil {
@@ -237,6 +238,7 @@ func (ng *AlertNG) init() error {
 						PromoteConfig:     true,
 						TenantID:          ng.Cfg.UnifiedAlerting.RemoteAlertmanager.TenantID,
 						URL:               ng.Cfg.UnifiedAlerting.RemoteAlertmanager.URL,
+						ExternalURL:       ng.Cfg.AppURL,
 					}
 					remoteAM, err := createRemoteAlertmanager(cfg, ng.KVStore, ng.SecretsService.Decrypt, autogenFn, m, ng.tracer)
 					if err != nil {
@@ -273,6 +275,7 @@ func (ng *AlertNG) init() error {
 						TenantID:          ng.Cfg.UnifiedAlerting.RemoteAlertmanager.TenantID,
 						URL:               ng.Cfg.UnifiedAlerting.RemoteAlertmanager.URL,
 						SyncInterval:      ng.Cfg.UnifiedAlerting.RemoteAlertmanager.SyncInterval,
+						ExternalURL:       ng.Cfg.AppURL,
 					}
 					remoteAM, err := createRemoteAlertmanager(cfg, ng.KVStore, ng.SecretsService.Decrypt, autogenFn, m, ng.tracer)
 					if err != nil {

pkg/services/ngalert/remote/alertmanager.go

@@ -77,10 +77,12 @@ type AlertmanagerConfig struct {
 	BasicAuthPassword string
 
 	DefaultConfig string
+
+	// ExternalURL is used in notifications sent by the remote Alertmanager.
+	ExternalURL string
 	// PromoteConfig is a flag that determines whether the configuration should be used in the remote Alertmanager.
 	// The same flag is used for promoting state.
 	PromoteConfig bool
-
 	// SyncInterval determines how often we should attempt to synchronize configuration.
 	SyncInterval time.Duration
 }
@@ -117,6 +119,7 @@ func NewAlertmanager(cfg AlertmanagerConfig, store stateStore, decryptFn Decrypt
 		TenantID:      cfg.TenantID,
 		URL:           u,
 		PromoteConfig: cfg.PromoteConfig,
+		ExternalURL:   cfg.ExternalURL,
 	}
 	mc, err := remoteClient.New(mcCfg, metrics, tracer)
 	if err != nil {

pkg/services/ngalert/remote/alertmanager_test.go

@@ -168,6 +168,7 @@ func TestApplyConfig(t *testing.T) {
 		DefaultConfig: defaultGrafanaConfig,
 		PromoteConfig: true,
 		SyncInterval:  1 * time.Hour,
+		ExternalURL:   "https://test.grafana.com",
 	}
 
 	ctx := context.Background()
@@ -198,6 +199,9 @@ func TestApplyConfig(t *testing.T) {
 	require.JSONEq(t, testGrafanaConfigWithSecret, string(amCfg))
 	require.True(t, configSent.Promoted)
 
+	// Grafana's URL should be sent alongside the configuration.
+	require.Equal(t, cfg.ExternalURL, configSent.ExternalURL)
+
 	// If we already got a 200 status code response and the sync interval hasn't elapsed,
 	// we shouldn't send the state/configuration again.
 	expStateSync := lastStateSync

pkg/services/ngalert/remote/client/alertmanager_configuration.go

@@ -21,6 +21,7 @@ type UserGrafanaConfig struct {
 	CreatedAt                 int64                         `json:"created"`
 	Default                   bool                          `json:"default"`
 	Promoted                  bool                          `json:"promoted"`
+	ExternalURL               string                        `json:"external_url"`
 }
 
 func (mc *Mimir) ShouldPromoteConfig() bool {
@@ -53,6 +54,7 @@ func (mc *Mimir) CreateGrafanaAlertmanagerConfig(ctx context.Context, cfg *apimo
 		CreatedAt:                 createdAt,
 		Default:                   isDefault,
 		Promoted:                  mc.promoteConfig,
+		ExternalURL:               mc.externalURL,
 	})
 	if err != nil {
 		return err

pkg/services/ngalert/remote/client/mimir.go

@@ -40,6 +40,7 @@ type Mimir struct {
 	logger        log.Logger
 	metrics       *metrics.RemoteAlertmanager
 	promoteConfig bool
+	externalURL   string
 }
 
 type Config struct {
@@ -49,6 +50,7 @@ type Config struct {
 
 	Logger        log.Logger
 	PromoteConfig bool
+	ExternalURL   string
 }
 
 // successResponse represents a successful response from the Mimir API.
@@ -91,6 +93,7 @@ func New(cfg *Config, metrics *metrics.RemoteAlertmanager, tracer tracing.Tracer
 		logger:        cfg.Logger,
 		metrics:       metrics,
 		promoteConfig: cfg.PromoteConfig,
+		externalURL:   cfg.ExternalURL,
 	}, nil
 }