Alerting: deactivate an Alertmanager configuration (#36794)

* Alerting: deactivate an Alertmanager configuration

Implement DELETE /api/alertmanager/grafana/config/api/v1/alerts
by storing the default configuration which stops existing cnfiguration
from being in use.

* Apply suggestions from code review

pkg/services/ngalert/api/api.go

@@ -25,6 +25,7 @@ var timeNow = time.Now
 type Alertmanager interface {
 	// Configuration
 	SaveAndApplyConfig(config *apimodels.PostableUserConfig) error
+	SaveAndApplyDefaultConfig() error
 	GetStatus() apimodels.GettableStatus
 
 	// Silences

pkg/services/ngalert/api/api_alertmanager.go

@@ -45,8 +45,15 @@ func (srv AlertmanagerSrv) RouteCreateSilence(c *models.ReqContext, postableSile
 }
 
 func (srv AlertmanagerSrv) RouteDeleteAlertingConfig(c *models.ReqContext) response.Response {
-	// not implemented
-	return NotImplementedResp
+	if !c.HasUserRole(models.ROLE_EDITOR) {
+		return ErrResp(http.StatusForbidden, errors.New("permission denied"), "")
+	}
+	if err := srv.am.SaveAndApplyDefaultConfig(); err != nil {
+		srv.log.Error("unable to save and apply default alertmanager configuration", "err", err)
+		return ErrResp(http.StatusInternalServerError, err, "failed to save and apply default Alertmanager configuration")
+	}
+
+	return response.JSON(http.StatusAccepted, util.DynMap{"message": "configuration deleted; the default is applied"})
 }
 
 func (srv AlertmanagerSrv) RouteDeleteSilence(c *models.ReqContext) response.Response {

pkg/services/ngalert/notifier/alertmanager.go

@@ -201,6 +201,37 @@ func (am *Alertmanager) StopAndWait() error {
 	return nil
 }
 
+// SaveAndApplyDefaultConfig saves the default configuration the database and applies the configuration to the Alertmanager.
+// It rollbacks the save if we fail to apply the configuration.
+func (am *Alertmanager) SaveAndApplyDefaultConfig() error {
+	am.reloadConfigMtx.Lock()
+	defer am.reloadConfigMtx.Unlock()
+
+	cmd := &ngmodels.SaveAlertmanagerConfigurationCmd{
+		AlertmanagerConfiguration: alertmanagerDefaultConfiguration,
+		Default:                   true,
+		ConfigurationVersion:      fmt.Sprintf("v%d", ngmodels.AlertConfigurationVersion),
+	}
+
+	cfg, err := Load([]byte(alertmanagerDefaultConfiguration))
+	if err != nil {
+		return err
+	}
+
+	err = am.Store.SaveAlertmanagerConfigurationWithCallback(cmd, func() error {
+		if err := am.applyConfig(cfg, []byte(alertmanagerDefaultConfiguration)); err != nil {
+			return err
+		}
+		return nil
+	})
+	if err != nil {
+		return err
+	}
+	am.Metrics.ActiveConfigurations.Set(1)
+
+	return nil
+}
+
 // SaveAndApplyConfig saves the configuration the database and applies the configuration to the Alertmanager.
 // It rollbacks the save if we fail to apply the configuration.
 func (am *Alertmanager) SaveAndApplyConfig(cfg *apimodels.PostableUserConfig) error {