Implement resilient watchcache initialization post-start-hook

cmd/kube-apiserver/app/options/options_test.go

@@ -139,16 +139,17 @@ func TestAddFlags(t *testing.T) {
 	expected := &ServerRunOptions{
 		Options: &controlplaneapiserver.Options{
 			GenericServerRunOptions: &apiserveroptions.ServerRunOptions{
-				AdvertiseAddress:            netutils.ParseIPSloppy("192.168.10.10"),
+				AdvertiseAddress:             netutils.ParseIPSloppy("192.168.10.10"),
-				CorsAllowedOriginList:       []string{"10.10.10.100", "10.10.10.200"},
+				CorsAllowedOriginList:        []string{"10.10.10.100", "10.10.10.200"},
-				MaxRequestsInFlight:         400,
+				MaxRequestsInFlight:          400,
-				MaxMutatingRequestsInFlight: 200,
+				MaxMutatingRequestsInFlight:  200,
-				RequestTimeout:              time.Duration(2) * time.Minute,
+				RequestTimeout:               time.Duration(2) * time.Minute,
-				MinRequestTimeout:           1800,
+				MinRequestTimeout:            1800,
-				JSONPatchMaxCopyBytes:       int64(3 * 1024 * 1024),
+				StorageInitializationTimeout: time.Minute,
-				MaxRequestBodyBytes:         int64(3 * 1024 * 1024),
+				JSONPatchMaxCopyBytes:        int64(3 * 1024 * 1024),
-				ComponentGlobalsRegistry:    componentGlobalsRegistry,
+				MaxRequestBodyBytes:          int64(3 * 1024 * 1024),
-				ComponentName:               utilversion.DefaultKubeComponent,
+				ComponentGlobalsRegistry:     componentGlobalsRegistry,
+				ComponentName:                utilversion.DefaultKubeComponent,
 			},
 			Admission: &kubeoptions.AdmissionOptions{
 				GenericAdmission: &apiserveroptions.AdmissionOptions{

pkg/controlplane/apiserver/options/options_test.go

@@ -123,16 +123,17 @@ func TestAddFlags(t *testing.T) {
 	// This is a snapshot of expected options parsed by args.
 	expected := &Options{
 		GenericServerRunOptions: &apiserveroptions.ServerRunOptions{
-			AdvertiseAddress:            netutils.ParseIPSloppy("192.168.10.10"),
+			AdvertiseAddress:             netutils.ParseIPSloppy("192.168.10.10"),
-			CorsAllowedOriginList:       []string{"10.10.10.100", "10.10.10.200"},
+			CorsAllowedOriginList:        []string{"10.10.10.100", "10.10.10.200"},
-			MaxRequestsInFlight:         400,
+			MaxRequestsInFlight:          400,
-			MaxMutatingRequestsInFlight: 200,
+			MaxMutatingRequestsInFlight:  200,
-			RequestTimeout:              time.Duration(2) * time.Minute,
+			RequestTimeout:               time.Duration(2) * time.Minute,
-			MinRequestTimeout:           1800,
+			MinRequestTimeout:            1800,
-			JSONPatchMaxCopyBytes:       int64(3 * 1024 * 1024),
+			StorageInitializationTimeout: time.Minute,
-			MaxRequestBodyBytes:         int64(3 * 1024 * 1024),
+			JSONPatchMaxCopyBytes:        int64(3 * 1024 * 1024),
-			ComponentGlobalsRegistry:    componentGlobalsRegistry,
+			MaxRequestBodyBytes:          int64(3 * 1024 * 1024),
-			ComponentName:               utilversion.DefaultKubeComponent,
+			ComponentGlobalsRegistry:     componentGlobalsRegistry,
+			ComponentName:                utilversion.DefaultKubeComponent,
 		},
 		Admission: &kubeoptions.AdmissionOptions{
 			GenericAdmission: &apiserveroptions.AdmissionOptions{

pkg/controlplane/apiserver/server.go

@@ -245,6 +245,10 @@ func (c completedConfig) New(name string, delegationTarget genericapiserver.Dele
 		})
 	}
 
+	if utilfeature.DefaultFeatureGate.Enabled(apiserverfeatures.WatchCacheInitializationPostStartHook) {
+		s.GenericAPIServer.AddPostStartHookOrDie("storage-readiness", s.GenericAPIServer.StorageReadinessHook.Hook)
+	}
+
 	s.GenericAPIServer.AddPostStartHookOrDie("start-legacy-token-tracking-controller", func(hookContext genericapiserver.PostStartHookContext) error {
 		go legacytokentracking.NewController(client).Run(hookContext.StopCh)
 		return nil

pkg/features/kube_features.go

@@ -1275,6 +1275,8 @@ var defaultKubernetesFeatureGates = map[featuregate.Feature]featuregate.FeatureS
 
 	genericfeatures.WatchBookmark: {Default: true, PreRelease: featuregate.GA, LockToDefault: true},
 
+	genericfeatures.WatchCacheInitializationPostStartHook: {Default: false, PreRelease: featuregate.Beta},
+
 	genericfeatures.WatchFromStorageWithoutResourceVersion: {Default: false, PreRelease: featuregate.Beta},
 
 	genericfeatures.WatchList: {Default: false, PreRelease: featuregate.Alpha},

staging/src/k8s.io/apiserver/pkg/features/kube_features.go

@@ -290,6 +290,12 @@ const (
 	// Enables support for watch bookmark events.
 	WatchBookmark featuregate.Feature = "WatchBookmark"
 
+	// owner: @wojtek-t
+	// beta: v1.31
+	//
+	// Enables post-start-hook for storage readiness
+	WatchCacheInitializationPostStartHook featuregate.Feature = "WatchCacheInitializationPostStartHook"
+
 	// owner: @serathius
 	// beta: 1.30
 	// Enables watches without resourceVersion to be served from storage.
@@ -407,6 +413,8 @@ var defaultKubernetesFeatureGates = map[featuregate.Feature]featuregate.FeatureS
 
 	WatchBookmark: {Default: true, PreRelease: featuregate.GA, LockToDefault: true},
 
+	WatchCacheInitializationPostStartHook: {Default: false, PreRelease: featuregate.Beta},
+
 	WatchFromStorageWithoutResourceVersion: {Default: false, PreRelease: featuregate.Beta},
 
 	InPlacePodVerticalScaling: {Default: false, PreRelease: featuregate.Alpha},

staging/src/k8s.io/apiserver/pkg/registry/generic/registry/store.go

@@ -226,6 +226,10 @@ type Store struct {
 	// storageVersionHash as empty in the discovery document.
 	StorageVersioner runtime.GroupVersioner
 
+	// ReadinessCheckFunc checks if the storage is ready for accepting requests.
+	// The field is optional, if set needs to be thread-safe.
+	ReadinessCheckFunc func() error
+
 	// DestroyFunc cleans up clients used by the underlying Storage; optional.
 	// If set, DestroyFunc has to be implemented in thread-safe way and
 	// be prepared for being called more than once.
@@ -234,6 +238,7 @@ type Store struct {
 
 // Note: the rest.StandardStorage interface aggregates the common REST verbs
 var _ rest.StandardStorage = &Store{}
+var _ rest.StorageWithReadiness = &Store{}
 var _ rest.TableConvertor = &Store{}
 var _ GenericStore = &Store{}
 
@@ -292,6 +297,14 @@ func (e *Store) New() runtime.Object {
 	return e.NewFunc()
 }
 
+// ReadinessCheck checks if the storage is ready for accepting requests.
+func (e *Store) ReadinessCheck() error {
+	if e.ReadinessCheckFunc != nil {
+		return e.ReadinessCheckFunc()
+	}
+	return nil
+}
+
 // Destroy cleans up its resources on shutdown.
 func (e *Store) Destroy() {
 	if e.DestroyFunc != nil {
@@ -1614,6 +1627,9 @@ func (e *Store) CompleteWithOptions(options *generic.StoreOptions) error {
 			}
 		}
 	}
+	if e.Storage.Storage != nil {
+		e.ReadinessCheckFunc = e.Storage.Storage.ReadinessCheck
+	}
 
 	return nil
 }

staging/src/k8s.io/apiserver/pkg/registry/rest/rest.go

@@ -52,6 +52,8 @@ import (
 // Storage is a generic interface for RESTful storage services.
 // Resources which are exported to the RESTful API of apiserver need to implement this interface. It is expected
 // that objects may implement any of the below interfaces.
+//
+// Consider using StorageWithReadiness whenever possible.
 type Storage interface {
 	// New returns an empty object that can be used with Create and Update after request data has been put into it.
 	// This object must be a pointer type for use with Codec.DecodeInto([]byte, runtime.Object)
@@ -63,6 +65,14 @@ type Storage interface {
 	Destroy()
 }
 
+// StorageWithReadiness extends Storage interface with the readiness check.
+type StorageWithReadiness interface {
+	Storage
+
+	// ReadinessCheck allows for checking storage readiness.
+	ReadinessCheck() error
+}
+
 // Scoper indicates what scope the resource is at. It must be specified.
 // It is usually provided automatically based on your strategy.
 type Scoper interface {

staging/src/k8s.io/apiserver/pkg/server/config.go

@@ -216,6 +216,10 @@ type Config struct {
 	// twice this value.  Note that it is up to the request handlers to ignore or honor this timeout. In seconds.
 	MinRequestTimeout int
 
+	// StorageInitializationTimeout defines the maximum amount of time to wait for storage initialization
+	// before declaring apiserver ready.
+	StorageInitializationTimeout time.Duration
+
 	// This represents the maximum amount of time it should take for apiserver to complete its startup
 	// sequence and become healthy. From apiserver's start time to when this amount of time has
 	// elapsed, /livez will assume that unfinished post-start hooks will complete successfully and
@@ -426,6 +430,7 @@ func NewConfig(codecs serializer.CodecFactory) *Config {
 		MaxMutatingRequestsInFlight:    200,
 		RequestTimeout:                 time.Duration(60) * time.Second,
 		MinRequestTimeout:              1800,
+		StorageInitializationTimeout:   time.Minute,
 		LivezGracePeriod:               time.Duration(0),
 		ShutdownDelayDuration:          time.Duration(0),
 		// 1.5MB is the default client request size in bytes
@@ -824,6 +829,7 @@ func (c completedConfig) New(name string, delegationTarget DelegationTarget) (*G
 		ShutdownSendRetryAfter: c.ShutdownSendRetryAfter,
 
 		APIServerID:           c.APIServerID,
+		StorageReadinessHook:  NewStorageReadinessHook(c.StorageInitializationTimeout),
 		StorageVersionManager: c.StorageVersionManager,
 
 		EffectiveVersion: c.EffectiveVersion,

staging/src/k8s.io/apiserver/pkg/server/genericapiserver.go

@@ -233,6 +233,10 @@ type GenericAPIServer struct {
 	// APIServerID is the ID of this API server
 	APIServerID string
 
+	// StorageReadinessHook implements post-start-hook functionality for checking readiness
+	// of underlying storage for registered resources.
+	StorageReadinessHook *StorageReadinessHook
+
 	// StorageVersionManager holds the storage versions of the API resources installed by this server.
 	StorageVersionManager storageversion.Manager
 
@@ -844,6 +848,7 @@ func (s *GenericAPIServer) InstallLegacyAPIGroup(apiPrefix string, apiGroupInfo
 	} else {
 		s.Handler.GoRestfulContainer.Add(legacyRootAPIHandler.WebService())
 	}
+	s.registerStorageReadinessCheck("", apiGroupInfo)
 
 	return nil
 }
@@ -902,10 +907,28 @@ func (s *GenericAPIServer) InstallAPIGroups(apiGroupInfos ...*APIGroupInfo) erro
 
 		s.DiscoveryGroupManager.AddGroup(apiGroup)
 		s.Handler.GoRestfulContainer.Add(discovery.NewAPIGroupHandler(s.Serializer, apiGroup).WebService())
+		s.registerStorageReadinessCheck(apiGroupInfo.PrioritizedVersions[0].Group, apiGroupInfo)
 	}
 	return nil
 }
 
+// registerStorageReadinessCheck registers the readiness checks for all underlying storages
+// for a given APIGroup.
+func (s *GenericAPIServer) registerStorageReadinessCheck(groupName string, apiGroupInfo *APIGroupInfo) {
+	for version, storageMap := range apiGroupInfo.VersionedResourcesStorageMap {
+		for resource, storage := range storageMap {
+			if withReadiness, ok := storage.(rest.StorageWithReadiness); ok {
+				gvr := metav1.GroupVersionResource{
+					Group:    groupName,
+					Version:  version,
+					Resource: resource,
+				}
+				s.StorageReadinessHook.RegisterStorage(gvr, withReadiness)
+			}
+		}
+	}
+}
+
 // InstallAPIGroup exposes the given api group in the API.
 // The <apiGroupInfo> passed into this function shouldn't be used elsewhere as the
 // underlying storage will be destroyed on this servers shutdown.

staging/src/k8s.io/apiserver/pkg/server/options/server_run_options.go

@@ -47,16 +47,17 @@ const (
 type ServerRunOptions struct {
 	AdvertiseAddress net.IP
 
-	CorsAllowedOriginList       []string
+	CorsAllowedOriginList        []string
-	HSTSDirectives              []string
+	HSTSDirectives               []string
-	ExternalHost                string
+	ExternalHost                 string
-	MaxRequestsInFlight         int
+	MaxRequestsInFlight          int
-	MaxMutatingRequestsInFlight int
+	MaxMutatingRequestsInFlight  int
-	RequestTimeout              time.Duration
+	RequestTimeout               time.Duration
-	GoawayChance                float64
+	GoawayChance                 float64
-	LivezGracePeriod            time.Duration
+	LivezGracePeriod             time.Duration
-	MinRequestTimeout           int
+	MinRequestTimeout            int
-	ShutdownDelayDuration       time.Duration
+	StorageInitializationTimeout time.Duration
+	ShutdownDelayDuration        time.Duration
 	// We intentionally did not add a flag for this option. Users of the
 	// apiserver library can wire it to a flag.
 	JSONPatchMaxCopyBytes int64
@@ -116,6 +117,7 @@ func NewServerRunOptionsForComponent(componentName string, componentGlobalsRegis
 		RequestTimeout:                      defaults.RequestTimeout,
 		LivezGracePeriod:                    defaults.LivezGracePeriod,
 		MinRequestTimeout:                   defaults.MinRequestTimeout,
+		StorageInitializationTimeout:        defaults.StorageInitializationTimeout,
 		ShutdownDelayDuration:               defaults.ShutdownDelayDuration,
 		ShutdownWatchTerminationGracePeriod: defaults.ShutdownWatchTerminationGracePeriod,
 		JSONPatchMaxCopyBytes:               defaults.JSONPatchMaxCopyBytes,
@@ -140,6 +142,7 @@ func (s *ServerRunOptions) ApplyTo(c *server.Config) error {
 	c.RequestTimeout = s.RequestTimeout
 	c.GoawayChance = s.GoawayChance
 	c.MinRequestTimeout = s.MinRequestTimeout
+	c.StorageInitializationTimeout = s.StorageInitializationTimeout
 	c.ShutdownDelayDuration = s.ShutdownDelayDuration
 	c.JSONPatchMaxCopyBytes = s.JSONPatchMaxCopyBytes
 	c.MaxRequestBodyBytes = s.MaxRequestBodyBytes
@@ -197,6 +200,10 @@ func (s *ServerRunOptions) Validate() []error {
 		errors = append(errors, fmt.Errorf("--min-request-timeout can not be negative value"))
 	}
 
+	if s.StorageInitializationTimeout < 0 {
+		errors = append(errors, fmt.Errorf("--storage-initialization-timeout can not be negative value"))
+	}
+
 	if s.ShutdownDelayDuration < 0 {
 		errors = append(errors, fmt.Errorf("--shutdown-delay-duration can not be negative value"))
 	}
@@ -350,6 +357,9 @@ func (s *ServerRunOptions) AddUniversalFlags(fs *pflag.FlagSet) {
 		"handler, which picks a randomized value above this number as the connection timeout, "+
 		"to spread out load.")
 
+	fs.DurationVar(&s.StorageInitializationTimeout, "storage-initialization-timeout", s.StorageInitializationTimeout,
+		"Maximum amount of time to wait for storage initialization before declaring apiserver ready. Defaults to 1m.")
+
 	fs.DurationVar(&s.ShutdownDelayDuration, "shutdown-delay-duration", s.ShutdownDelayDuration, ""+
 		"Time to delay the termination. During that time the server keeps serving requests normally. The endpoints /healthz and /livez "+
 		"will return success, but /readyz immediately returns failure. Graceful termination starts after this delay "+

staging/src/k8s.io/apiserver/pkg/server/storage_readiness_hook.go

@@ -0,0 +1,91 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package server
+
+import (
+	"context"
+	"errors"
+	"sync"
+	"time"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/util/wait"
+	"k8s.io/apiserver/pkg/registry/rest"
+	"k8s.io/klog/v2"
+)
+
+// StorageReadinessHook implements PostStartHook functionality for checking readiness
+// of underlying storage for registered resources.
+type StorageReadinessHook struct {
+	timeout time.Duration
+
+	lock   sync.Mutex
+	checks map[string]func() error
+}
+
+// NewStorageReadinessHook created new StorageReadinessHook.
+func NewStorageReadinessHook(timeout time.Duration) *StorageReadinessHook {
+	return &StorageReadinessHook{
+		checks:  make(map[string]func() error),
+		timeout: timeout,
+	}
+}
+
+func (h *StorageReadinessHook) RegisterStorage(gvr metav1.GroupVersionResource, storage rest.StorageWithReadiness) {
+	h.lock.Lock()
+	defer h.lock.Unlock()
+
+	if _, ok := h.checks[gvr.String()]; !ok {
+		h.checks[gvr.String()] = storage.ReadinessCheck
+	} else {
+		klog.Errorf("Registering storage readiness hook for %s again: ", gvr.String())
+	}
+}
+
+func (h *StorageReadinessHook) check() bool {
+	h.lock.Lock()
+	defer h.lock.Unlock()
+
+	failedChecks := []string{}
+	for gvr, check := range h.checks {
+		if err := check(); err != nil {
+			failedChecks = append(failedChecks, gvr)
+		}
+	}
+	if len(failedChecks) == 0 {
+		klog.Infof("Storage is ready for all registered resources")
+		return true
+	}
+	klog.V(4).Infof("Storage is not ready for: %v", failedChecks)
+	return false
+}
+
+func (h *StorageReadinessHook) Hook(ctx PostStartHookContext) error {
+	deadlineCtx, cancel := context.WithTimeout(ctx, h.timeout)
+	defer cancel()
+	err := wait.PollUntilContextCancel(deadlineCtx, 100*time.Millisecond, true,
+		func(_ context.Context) (bool, error) {
+			if ok := h.check(); ok {
+				return true, nil
+			}
+			return false, nil
+		})
+	if errors.Is(err, context.DeadlineExceeded) {
+		klog.Warningf("Deadline exceeded while waiting for storage readiness... ignoring")
+	}
+	return nil
+}

staging/src/k8s.io/apiserver/pkg/server/storage_readiness_hook_test.go

@@ -0,0 +1,85 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package server
+
+import (
+	"context"
+	"fmt"
+	"testing"
+	"time"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+)
+
+type fakeReadinessStorage struct {
+	result error
+}
+
+func (s *fakeReadinessStorage) New() runtime.Object   { return nil }
+func (s *fakeReadinessStorage) Destroy()              {}
+func (s *fakeReadinessStorage) ReadinessCheck() error { return s.result }
+
+func testGVR(index int) metav1.GroupVersionResource {
+	return metav1.GroupVersionResource{
+		Group:    "group",
+		Version:  "version",
+		Resource: fmt.Sprintf("resource-%d", index),
+	}
+}
+
+func TestStorageReadinessHook(t *testing.T) {
+	h := NewStorageReadinessHook(time.Second)
+
+	numChecks := 5
+	storages := make([]*fakeReadinessStorage, numChecks)
+	for i := 0; i < numChecks; i++ {
+		storages[i] = &fakeReadinessStorage{
+			result: fmt.Errorf("failed"),
+		}
+		h.RegisterStorage(testGVR(i), storages[i])
+	}
+
+	for i := 0; i < numChecks; i++ {
+		if ok := h.check(); ok {
+			t.Errorf("%d: unexpected check pass", i)
+		}
+		storages[i].result = nil
+	}
+	if ok := h.check(); !ok {
+		t.Errorf("unexpected check failure")
+	}
+}
+
+func TestStorageReadinessHookTimeout(t *testing.T) {
+	h := NewStorageReadinessHook(time.Second)
+
+	storage := &fakeReadinessStorage{
+		result: fmt.Errorf("failed"),
+	}
+	h.RegisterStorage(testGVR(0), storage)
+
+	ctx := context.Background()
+	hookCtx := PostStartHookContext{
+		LoopbackClientConfig: nil,
+		StopCh:               ctx.Done(),
+		Context:              ctx,
+	}
+	if err := h.Hook(hookCtx); err != nil {
+		t.Errorf("unexpected hook failure on timeout")
+	}
+}

staging/src/k8s.io/apiserver/pkg/storage/cacher/cacher.go

@@ -962,6 +962,14 @@ func (c *Cacher) Count(pathPrefix string) (int64, error) {
 	return c.storage.Count(pathPrefix)
 }
 
+// ReadinessCheck implements storage.Interface.
+func (c *Cacher) ReadinessCheck() error {
+	if !c.ready.check() {
+		return storage.ErrStorageNotReady
+	}
+	return nil
+}
+
 // baseObjectThreadUnsafe omits locking for cachingObject.
 func baseObjectThreadUnsafe(object runtime.Object) runtime.Object {
 	if co, ok := object.(*cachingObject); ok {

staging/src/k8s.io/apiserver/pkg/storage/cacher/cacher_whitebox_test.go

@@ -181,6 +181,9 @@ func (d *dummyStorage) GuaranteedUpdate(_ context.Context, _ string, _ runtime.O
 func (d *dummyStorage) Count(_ string) (int64, error) {
 	return 0, fmt.Errorf("unimplemented")
 }
+func (d *dummyStorage) ReadinessCheck() error {
+	return nil
+}
 func (d *dummyStorage) injectError(err error) {
 	d.Lock()
 	defer d.Unlock()

staging/src/k8s.io/apiserver/pkg/storage/errors.go

@@ -25,7 +25,10 @@ import (
 	"k8s.io/apimachinery/pkg/util/validation/field"
 )
 
-var ErrResourceVersionSetOnCreate = errors.New("resourceVersion should not be set on objects to be created")
+var (
+	ErrResourceVersionSetOnCreate = errors.New("resourceVersion should not be set on objects to be created")
+	ErrStorageNotReady            = errors.New("storage not ready")
+)
 
 const (
 	ErrCodeKeyNotFound int = iota + 1

staging/src/k8s.io/apiserver/pkg/storage/etcd3/store.go

@@ -591,6 +591,11 @@ func (s *store) Count(key string) (int64, error) {
 	return getResp.Count, nil
 }
 
+// ReadinessCheck implements storage.Interface.
+func (s *store) ReadinessCheck() error {
+	return nil
+}
+
 // resolveGetListRev is used by GetList to resolve the rev to use in the client.KV.Get request.
 func (s *store) resolveGetListRev(continueKey string, continueRV int64, opts storage.ListOptions) (int64, error) {
 	var withRev int64

staging/src/k8s.io/apiserver/pkg/storage/interfaces.go

@@ -243,6 +243,9 @@ type Interface interface {
 	// Count returns number of different entries under the key (generally being path prefix).
 	Count(key string) (int64, error)
 
+	// ReadinessCheck checks if the storage is ready for accepting requests.
+	ReadinessCheck() error
+
 	// RequestWatchProgress requests the a watch stream progress status be sent in the
 	// watch response stream as soon as possible.
 	// Used for monitor watch progress even if watching resources with no changes.

test/e2e/apimachinery/health_handlers.go

@@ -24,6 +24,8 @@ import (
 
 	"k8s.io/apimachinery/pkg/util/sets"
 	"k8s.io/apimachinery/pkg/util/wait"
+	apiserverfeatures "k8s.io/apiserver/pkg/features"
+	utilfeature "k8s.io/apiserver/pkg/util/feature"
 	clientset "k8s.io/client-go/kubernetes"
 	restclient "k8s.io/client-go/rest"
 	"k8s.io/kubernetes/test/e2e/framework"
@@ -126,6 +128,13 @@ var _ = SIGDescribe("health handlers", func() {
 	f.NamespacePodSecurityLevel = admissionapi.LevelPrivileged
 
 	ginkgo.It("should contain necessary checks", func(ctx context.Context) {
+		if utilfeature.DefaultFeatureGate.Enabled(apiserverfeatures.WatchCacheInitializationPostStartHook) {
+			storageReadinessCheck := "[+]poststarthook/storage-readiness ok"
+			requiredHealthzChecks.Insert(storageReadinessCheck)
+			requiredLivezChecks.Insert(storageReadinessCheck)
+			requiredReadyzChecks.Insert(storageReadinessCheck)
+		}
+
 		ginkgo.By("/health")
 		err := testPath(ctx, f.ClientSet, "/healthz?verbose=1", requiredHealthzChecks)
 		framework.ExpectNoError(err)