Add /readyz for kube-scheduler

/readyz contains `sched-handler-sync`, `leaderElection` (when election is
enabled) and `shutdown` checks

Kubernetes-commit: 44c08fdbd592b7c167ad0c3b0b4a3b52b99c116f

pkg/server/healthz.go

@@ -118,7 +118,7 @@ func (s *GenericAPIServer) AddLivezChecks(delay time.Duration, checks ...healthz
 // that we can register that the api-server is no longer ready while we attempt to gracefully
 // shutdown.
 func (s *GenericAPIServer) addReadyzShutdownCheck(stopCh <-chan struct{}) error {
-	return s.AddReadyzChecks(shutdownCheck{stopCh})
+	return s.AddReadyzChecks(healthz.NewShutdownHealthz(stopCh))
 }
 
 // installHealthz creates the healthz endpoint for this server
@@ -139,25 +139,6 @@ func (s *GenericAPIServer) installLivez() {
 	s.livezRegistry.installHandler(s.Handler.NonGoRestfulMux)
 }
 
-// shutdownCheck fails if the embedded channel is closed. This is intended to allow for graceful shutdown sequences
-// for the apiserver.
-type shutdownCheck struct {
-	StopCh <-chan struct{}
-}
-
-func (shutdownCheck) Name() string {
-	return "shutdown"
-}
-
-func (c shutdownCheck) Check(req *http.Request) error {
-	select {
-	case <-c.StopCh:
-		return fmt.Errorf("process is shutting down")
-	default:
-	}
-	return nil
-}
-
 // delayedHealthCheck wraps a health check which will not fail until the explicitly defined delay has elapsed. This
 // is intended for use primarily for livez health checks.
 func delayedHealthCheck(check healthz.HealthChecker, clock clock.Clock, delay time.Duration) healthz.HealthChecker {

pkg/server/healthz/healthz.go

@@ -105,6 +105,29 @@ func (i *informerSync) Name() string {
 	return "informer-sync"
 }
 
+type shutdown struct {
+	stopCh <-chan struct{}
+}
+
+// NewShutdownHealthz returns a new HealthChecker that will fail if the embedded channel is closed.
+// This is intended to allow for graceful shutdown sequences.
+func NewShutdownHealthz(stopCh <-chan struct{}) HealthChecker {
+	return &shutdown{stopCh}
+}
+
+func (s *shutdown) Name() string {
+	return "shutdown"
+}
+
+func (s *shutdown) Check(req *http.Request) error {
+	select {
+	case <-s.stopCh:
+		return fmt.Errorf("process is shutting down")
+	default:
+	}
+	return nil
+}
+
 func (i *informerSync) Check(_ *http.Request) error {
 	stopCh := make(chan struct{})
 	// Close stopCh to force checking if informers are synced now.