[release-0.17] 🐛 Reintroduce AddMetricsServerExtraHandler on manager

pkg/manager/internal.go

@@ -179,6 +179,24 @@ func (cm *controllerManager) add(r Runnable) error {
 	return cm.runnables.Add(r)
 }
 
+// AddMetricsServerExtraHandler adds extra handler served on path to the http server that serves metrics.
+func (cm *controllerManager) AddMetricsServerExtraHandler(path string, handler http.Handler) error {
+	cm.Lock()
+	defer cm.Unlock()
+	if cm.started {
+		return fmt.Errorf("unable to add new metrics handler because metrics endpoint has already been created")
+	}
+	if cm.metricsServer == nil {
+		cm.GetLogger().Info("warn: metrics server is currently disabled, registering extra handler %q will be ignored", path)
+		return nil
+	}
+	if err := cm.metricsServer.AddExtraHandler(path, handler); err != nil {
+		return err
+	}
+	cm.logger.V(2).Info("Registering metrics http server extra handler", "path", path)
+	return nil
+}
+
 // AddHealthzCheck allows you to add Healthz checker.
 func (cm *controllerManager) AddHealthzCheck(name string, check healthz.Checker) error {
 	cm.Lock()

pkg/manager/manager.go

@@ -67,6 +67,15 @@ type Manager interface {
 	// election was configured.
 	Elected() <-chan struct{}
 
+	// AddMetricsServerExtraHandler adds an extra handler served on path to the http server that serves metrics.
+	// Might be useful to register some diagnostic endpoints e.g. pprof.
+	//
+	// Note that these endpoints are meant to be sensitive and shouldn't be exposed publicly.
+	//
+	// If the simple path -> handler mapping offered here is not enough,
+	// a new http server/listener should be added as Runnable to the manager via Add method.
+	AddMetricsServerExtraHandler(path string, handler http.Handler) error
+
 	// AddHealthzCheck allows you to add Healthz checker
 	AddHealthzCheck(name string, check healthz.Checker) error
 

pkg/manager/manager_test.go

@@ -1453,6 +1453,12 @@ var _ = Describe("manger.Manager", func() {
 				m, err := New(cfg, opts)
 				Expect(err).NotTo(HaveOccurred())
 
+				// Should error when we add another extra endpoint on the already registered path.
+				err = m.AddMetricsServerExtraHandler("/debug", http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+					_, _ = w.Write([]byte("Another debug info"))
+				}))
+				Expect(err).To(HaveOccurred())
+
 				ctx, cancel := context.WithCancel(context.Background())
 				defer cancel()
 				go func() {

pkg/metrics/server/server.go

@@ -46,6 +46,9 @@ var DefaultBindAddress = ":8080"
 
 // Server is a server that serves metrics.
 type Server interface {
+	// AddExtraHandler adds extra handler served on path to the http server that serves metrics.
+	AddExtraHandler(path string, handler http.Handler) error
+
 	// NeedLeaderElection implements the LeaderElectionRunnable interface, which indicates
 	// the metrics server doesn't need leader election.
 	NeedLeaderElection() bool
@@ -179,6 +182,23 @@ func (*defaultServer) NeedLeaderElection() bool {
 	return false
 }
 
+// AddExtraHandler adds extra handler served on path to the http server that serves metrics.
+func (s *defaultServer) AddExtraHandler(path string, handler http.Handler) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.options.ExtraHandlers == nil {
+		s.options.ExtraHandlers = make(map[string]http.Handler)
+	}
+	if path == defaultMetricsEndpoint {
+		return fmt.Errorf("overriding builtin %s endpoint is not allowed", defaultMetricsEndpoint)
+	}
+	if _, found := s.options.ExtraHandlers[path]; found {
+		return fmt.Errorf("can't register extra handler by duplicate path %q on metrics http server", path)
+	}
+	s.options.ExtraHandlers[path] = handler
+	return nil
+}
+
 // Start runs the server.
 // It will install the metrics related resources depend on the server configuration.
 func (s *defaultServer) Start(ctx context.Context) error {