Use Linkerd metrics when NGINX is the mesh ingress

Set the metrics provider to Linkerd Prometheus when using NGINX as Linkerd Ingress. This mitigates the lack of canary metrics in the NGINX controller exporter.

pkg/controller/scheduler.go

@@ -567,8 +567,19 @@ func (c *Controller) analyseCanary(r *flaggerv1.Canary) bool {
 		}
 	}
 
+	// override the global provider if one is specified in the canary spec
+	metricsProvider := c.meshProvider
+	if r.Spec.Provider != "" {
+		metricsProvider = r.Spec.Provider
+
+		// set the metrics provider to Linkerd Prometheus when using NGINX as Linkerd Ingress
+		if r.Spec.Provider == "nginx" && strings.Contains(c.meshProvider, "linkerd") {
+			metricsProvider = "linkerd"
+		}
+	}
+
 	// create observer based on the mesh provider
-	observer := c.observerFactory.Observer()
+	observer := c.observerFactory.Observer(metricsProvider)
 
 	// run metrics checks
 	for _, metric := range r.Spec.CanaryAnalysis.Metrics {

pkg/metrics/factory.go

@@ -22,29 +22,29 @@ func NewFactory(metricsServer string, meshProvider string, timeout time.Duration
 	}, nil
 }
 
-func (factory Factory) Observer() Interface {
+func (factory Factory) Observer(provider string) Interface {
 	switch {
-	case factory.MeshProvider == "none":
+	case provider == "none":
 		return &HttpObserver{
 			client: factory.Client,
 		}
-	case factory.MeshProvider == "appmesh":
+	case provider == "appmesh":
 		return &EnvoyObserver{
 			client: factory.Client,
 		}
-	case factory.MeshProvider == "nginx":
+	case provider == "nginx":
 		return &NginxObserver{
 			client: factory.Client,
 		}
-	case strings.HasPrefix(factory.MeshProvider, "gloo"):
+	case strings.HasPrefix(provider, "gloo"):
 		return &GlooObserver{
 			client: factory.Client,
 		}
-	case factory.MeshProvider == "smi:linkerd":
+	case provider == "smi:linkerd":
 		return &LinkerdObserver{
 			client: factory.Client,
 		}
-	case factory.MeshProvider == "linkerd":
+	case provider == "linkerd":
 		return &LinkerdObserver{
 			client: factory.Client,
 		}