add metric for tracking failure to start the controller-runtime manager (#1860)

Signed-off-by: Evan Baker <rbtr@users.noreply.github.com>

cns/service/main.go

@@ -1260,7 +1260,8 @@ func InitializeCRDState(ctx context.Context, httpRestService cns.HTTPService, cn
 			if err := manager.Start(ctx); err != nil {
 				logger.Errorf("[Azure CNS] Failed to start request controller: %v", err)
 				// retry to start the request controller
-				// todo: add a CNS metric to count # of failures
+				// inc the managerStartFailures metric for failure tracking
+				managerStartFailures.Inc()
 			} else {
 				logger.Printf("exiting NodeNetworkConfig reconciler")
 				return

cns/service/metrics.go

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"sigs.k8s.io/controller-runtime/pkg/metrics"
+)
+
+// managerStartFailures is a monotic counter which tracks the number of times the controller-runtime
+// manager failed to start. To drive alerting based on this metric, it is recommended to use the rate
+// of increase over a period of time. A positive rate of change indicates that the CNS is actively
+// failing and retrying.
+var managerStartFailures = prometheus.NewCounter(
+	prometheus.CounterOpts{
+		Name: "manager_start_failures_total",
+		Help: "Number of times the controller-runtime manager failed to start.",
+	},
+)
+
+func init() {
+	metrics.Registry.MustRegister(
+		managerStartFailures,
+	)
+}