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 {

pkg/tests/api/alerting/api_notification_channel_test.go

@@ -122,6 +122,30 @@ func TestNotificationChannels(t *testing.T) {
 	mockChannel.matchesExpNotifications(t, expNonEmailNotifications)
 	require.Equal(t, expEmailNotifications, mockEmail.emails)
 	require.NoError(t, mockChannel.Close())
+
+	{
+		// Delete the configuration; so it returns the default configuration.
+		u := fmt.Sprintf("http://grafana:password@%s/api/alertmanager/grafana/config/api/v1/alerts", grafanaListedAddr)
+		req, err := http.NewRequest(http.MethodDelete, u, nil)
+		require.NoError(t, err)
+		client := &http.Client{}
+		resp, err := client.Do(req)
+		require.NoError(t, err)
+		t.Cleanup(func() {
+			err := resp.Body.Close()
+			require.NoError(t, err)
+		})
+		b, err := ioutil.ReadAll(resp.Body)
+		require.NoError(t, err)
+		require.Equal(t, 202, resp.StatusCode)
+		require.JSONEq(t, `{"message":"configuration deleted; the default is applied"}`, string(b))
+
+		alertsURL := fmt.Sprintf("http://grafana:password@%s/api/alertmanager/grafana/config/api/v1/alerts", grafanaListedAddr)
+		resp = getRequest(t, alertsURL, http.StatusOK) // nolint
+		b, err = ioutil.ReadAll(resp.Body)
+		require.NoError(t, err)
+		require.JSONEq(t, defaultAlertmanagerConfigJSON, string(b))
+	}
 }
 
 func getAlertmanagerConfig(channelAddr string) string {