Alerting: Upload error image when image renderer unavailable (#23713)

When Include image is enabled for an alert notification channel, but there's 
no image renderer available/installed when sending notification an error 
image will be uploaded/attached explaining that you need to install the 
Grafana Image Renderer plugin.

Ref #13802

Co-Authored-By: Arve Knudsen <arve.knudsen@gmail.com>

pkg/services/alerting/notifier.go

@@ -53,25 +53,19 @@ func (n *notificationService) SendIfNeeded(evalCtx *EvalContext) error {
 	}
 
 	if notifierStates.ShouldUploadImage() {
-		if n.renderService.IsAvailable() {
-			// Create a copy of EvalContext and give it a new, shorter, timeout context to upload the image
-			uploadEvalCtx := *evalCtx
-			timeout := setting.AlertingNotificationTimeout / 2
-			var uploadCtxCancel func()
-			uploadEvalCtx.Ctx, uploadCtxCancel = context.WithTimeout(evalCtx.Ctx, timeout)
+		// Create a copy of EvalContext and give it a new, shorter, timeout context to upload the image
+		uploadEvalCtx := *evalCtx
+		timeout := setting.AlertingNotificationTimeout / 2
+		var uploadCtxCancel func()
+		uploadEvalCtx.Ctx, uploadCtxCancel = context.WithTimeout(evalCtx.Ctx, timeout)
 
-			// Try to upload the image without consuming all the time allocated for EvalContext
-			if err = n.renderAndUploadImage(&uploadEvalCtx, timeout); err != nil {
-				n.log.Error("Failed to render and upload alert panel image.", "ruleId", uploadEvalCtx.Rule.ID, "error", err)
-			}
-			uploadCtxCancel()
-			evalCtx.ImageOnDiskPath = uploadEvalCtx.ImageOnDiskPath
-			evalCtx.ImagePublicURL = uploadEvalCtx.ImagePublicURL
-		} else {
-			n.log.Warn("Could not render image for alert notification, no image renderer found/installed. " +
-				"For image rendering support please install the grafana-image-renderer plugin. " +
-				"Read more at https://grafana.com/docs/grafana/latest/administration/image_rendering/")
+		// Try to upload the image without consuming all the time allocated for EvalContext
+		if err = n.renderAndUploadImage(&uploadEvalCtx, timeout); err != nil {
+			n.log.Error("Failed to render and upload alert panel image.", "ruleId", uploadEvalCtx.Rule.ID, "error", err)
 		}
+		uploadCtxCancel()
+		evalCtx.ImageOnDiskPath = uploadEvalCtx.ImageOnDiskPath
+		evalCtx.ImagePublicURL = uploadEvalCtx.ImagePublicURL
 	}
 
 	return n.sendNotifications(evalCtx, notifierStates)
@@ -174,6 +168,7 @@ func (n *notificationService) renderAndUploadImage(evalCtx *EvalContext, timeout
 	n.log.Debug("Rendered alert panel image", "ruleId", evalCtx.Rule.ID, "path", result.FilePath, "took", took)
 
 	evalCtx.ImageOnDiskPath = result.FilePath
+
 	n.log.Debug("Uploading alert panel image to external image store", "ruleId", evalCtx.Rule.ID, "path", evalCtx.ImageOnDiskPath)
 
 	start = time.Now()

pkg/services/alerting/notifier_test.go

@@ -39,13 +39,13 @@ func TestNotificationService(t *testing.T) {
 		require.Truef(t, evalCtx.Ctx.Value(notificationSent{}).(bool), "expected notification to be sent, but wasn't")
 	})
 
-	notificationServiceScenario(t, "Given alert rule with upload image enabled but no renderer available should not render and upload image, but send notification", evalCtx, true, func(scenarioCtx *scenarioContext) {
+	notificationServiceScenario(t, "Given alert rule with upload image enabled but no renderer available should render and upload unavailable image and send notification", evalCtx, true, func(scenarioCtx *scenarioContext) {
 		scenarioCtx.rendererAvailable = false
 		err := scenarioCtx.notificationService.SendIfNeeded(evalCtx)
 		require.NoError(t, err)
 
-		require.Equalf(t, 0, scenarioCtx.renderCount, "expected render to not be called, but it was")
-		require.Equalf(t, 0, scenarioCtx.imageUploadCount, "expected image to not be uploaded, but it was")
+		require.Equalf(t, 1, scenarioCtx.renderCount, "expected render to be called, but it wasn't")
+		require.Equalf(t, 1, scenarioCtx.imageUploadCount, "expected image to be uploaded, but it wasn't")
 		require.Truef(t, evalCtx.Ctx.Value(notificationSent{}).(bool), "expected notification to be sent, but wasn't")
 	})
 

pkg/services/rendering/rendering.go

@@ -121,6 +121,14 @@ func (rs *RenderingService) RenderErrorImage(err error) (*RenderResult, error) {
 	}, nil
 }
 
+func (rs *RenderingService) renderUnavailableImage() *RenderResult {
+	imgPath := "public/img/rendering_plugin_not_installed.png"
+
+	return &RenderResult{
+		FilePath: filepath.Join(setting.HomePath, imgPath),
+	}
+}
+
 func (rs *RenderingService) Render(ctx context.Context, opts Opts) (*RenderResult, error) {
 	if rs.inProgressCount > opts.ConcurrentLimit {
 		return &RenderResult{
@@ -128,8 +136,11 @@ func (rs *RenderingService) Render(ctx context.Context, opts Opts) (*RenderResul
 		}, nil
 	}
 
-	if rs.renderAction == nil {
-		return nil, fmt.Errorf("no renderer found")
+	if !rs.IsAvailable() {
+		rs.log.Warn("Could not render image, no image renderer found/installed. " +
+			"For image rendering support please install the grafana-image-renderer plugin. " +
+			"Read more at https://grafana.com/docs/grafana/latest/administration/image_rendering/")
+		return rs.renderUnavailableImage(), nil
 	}
 
 	rs.log.Info("Rendering", "path", opts.Path)