✨ add health check for webhook server

pkg/webhook/server.go

@@ -32,6 +32,7 @@ import (
 	"k8s.io/apimachinery/pkg/runtime"
 	kscheme "k8s.io/client-go/kubernetes/scheme"
 	"sigs.k8s.io/controller-runtime/pkg/certwatcher"
+	"sigs.k8s.io/controller-runtime/pkg/healthz"
 	"sigs.k8s.io/controller-runtime/pkg/runtime/inject"
 	"sigs.k8s.io/controller-runtime/pkg/webhook/internal/metrics"
 )
@@ -87,6 +88,10 @@ type Server struct {
 	// defaultingOnce ensures that the default fields are only ever set once.
 	defaultingOnce sync.Once
 
+	// started is set to true immediately before the server is started
+	// and thus can be used to check if the server has been started
+	started bool
+
 	// mu protects access to the webhook map & setFields for Start, Register, etc
 	mu sync.Mutex
 }
@@ -272,6 +277,9 @@ func (s *Server) Start(ctx context.Context) error {
 		close(idleConnsClosed)
 	}()
 
+	s.mu.Lock()
+	s.started = true
+	s.mu.Unlock()
 	if err := srv.Serve(listener); err != nil && err != http.ErrServerClosed {
 		return err
 	}
@@ -280,6 +288,19 @@ func (s *Server) Start(ctx context.Context) error {
 	return nil
 }
 
+// StartedChecker returns an healthz.Checker which is healthy after the
+// server has been started.
+func (s *Server) StartedChecker() healthz.Checker {
+	return func(req *http.Request) error {
+		s.mu.Lock()
+		defer s.mu.Unlock()
+		if !s.started {
+			return fmt.Errorf("webhook server has not been started yet")
+		}
+		return nil
+	}
+}
+
 // InjectFunc injects the field setter into the server.
 func (s *Server) InjectFunc(f inject.Func) error {
 	s.setFields = f

pkg/webhook/server_test.go

@@ -137,6 +137,8 @@ var _ = Describe("Webhook Server", func() {
 				return ioutil.ReadAll(resp.Body)
 			}).Should(Equal([]byte("gadzooks!")))
 
+			Expect(server.StartedChecker()(nil)).To(Succeed())
+
 			ctxCancel()
 			Eventually(doneCh, "4s").Should(BeClosed())
 		})