Merge pull request #104281 from tkashem/not-ready-429

send retry-after until the apiserver is ready

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

@@ -240,6 +240,15 @@ type Config struct {
 	// rejected with a 429 status code and a 'Retry-After' response.
 	ShutdownSendRetryAfter bool
 
+	// StartupSendRetryAfterUntilReady once set will reject incoming requests with
+	// a 429 status code and a 'Retry-After' response header until the apiserver
+	// hasn't fully initialized.
+	// This option ensures that the system stays consistent even when requests
+	// are received before the server has been initialized.
+	// In particular, it prevents child deletion in case of GC or/and orphaned
+	// content in case of the namespaces controller.
+	StartupSendRetryAfterUntilReady bool
+
 	//===========================================================================
 	// values below here are targets for removal
 	//===========================================================================
@@ -473,6 +482,46 @@ func (c *Config) AddPostStartHookOrDie(name string, hook PostStartHookFunc) {
 	}
 }
 
+// shouldAddWithRetryAfterFilter returns an appropriate ShouldRespondWithRetryAfterFunc
+// if the apiserver should respond with a Retry-After response header based on option
+// 'shutdown-send-retry-after' or 'startup-send-retry-after-until-ready'.
+func (c *Config) shouldAddWithRetryAfterFilter() genericfilters.ShouldRespondWithRetryAfterFunc {
+	if !(c.ShutdownSendRetryAfter || c.StartupSendRetryAfterUntilReady) {
+		return nil
+	}
+
+	// follow lifecycle, avoiding go routines per request
+	const (
+		startup int32 = iota
+		running
+		terminating
+	)
+	state := startup
+	go func() {
+		<-c.lifecycleSignals.HasBeenReady.Signaled()
+		atomic.StoreInt32(&state, running)
+		<-c.lifecycleSignals.AfterShutdownDelayDuration.Signaled()
+		atomic.StoreInt32(&state, terminating)
+	}()
+
+	return func() (*genericfilters.RetryAfterParams, bool) {
+		state := atomic.LoadInt32(&state)
+		switch {
+		case c.StartupSendRetryAfterUntilReady && state == startup:
+			return &genericfilters.RetryAfterParams{
+				Message: "The apiserver hasn't been fully initialized yet, please try again later.",
+			}, true
+		case c.ShutdownSendRetryAfter && state == terminating:
+			return &genericfilters.RetryAfterParams{
+				TearDownConnection: true,
+				Message:            "The apiserver is shutting down, please try again later.",
+			}, true
+		default:
+			return nil, false
+		}
+	}
+}
+
 // Complete fills in any fields not set that are required to have valid data and can be derived
 // from other fields. If you're going to `ApplyOptions`, do that first. It's mutating the receiver.
 func (c *Config) Complete(informers informers.SharedInformerFactory) CompletedConfig {
@@ -799,8 +848,8 @@ func DefaultBuildHandlerChain(apiHandler http.Handler, c *Config) http.Handler {
 	handler = genericapifilters.WithWarningRecorder(handler)
 	handler = genericapifilters.WithCacheControl(handler)
 	handler = genericfilters.WithHSTS(handler, c.HSTSDirectives)
-	if c.ShutdownSendRetryAfter {
-		handler = genericfilters.WithRetryAfter(handler, c.lifecycleSignals.AfterShutdownDelayDuration.Signaled())
+	if shouldRespondWithRetryAfterFn := c.shouldAddWithRetryAfterFilter(); shouldRespondWithRetryAfterFn != nil {
+		handler = genericfilters.WithRetryAfter(handler, shouldRespondWithRetryAfterFn)
 	}
 	handler = genericfilters.WithHTTPLogging(handler)
 	if utilfeature.DefaultFeatureGate.Enabled(genericfeatures.APIServerTracing) {

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

@@ -38,6 +38,7 @@ import (
 	"k8s.io/apiserver/pkg/authentication/authenticator"
 	"k8s.io/apiserver/pkg/authentication/user"
 	"k8s.io/apiserver/pkg/endpoints/request"
+	genericfilters "k8s.io/apiserver/pkg/server/filters"
 	"k8s.io/apiserver/pkg/server/healthz"
 	"k8s.io/client-go/informers"
 	"k8s.io/client-go/kubernetes/fake"
@@ -345,6 +346,159 @@ func TestAuthenticationAuditAnnotationsDefaultChain(t *testing.T) {
 	}
 }
 
+func TestShouldRespondWithRetryAfterFunc(t *testing.T) {
+	tests := []struct {
+		name                            string
+		config                          *Config
+		addWithRetryAfterFilterExpected bool
+		sendRetryAfterExpected          bool
+		retryAfterParamsExpected        *genericfilters.RetryAfterParams
+	}{
+		{
+			name: "both shutdown-send-retry-after and startup-send-retry-after-until-ready are not enabled",
+			config: &Config{
+				StartupSendRetryAfterUntilReady: false,
+				ShutdownSendRetryAfter:          false,
+			},
+			addWithRetryAfterFilterExpected: false,
+			sendRetryAfterExpected:          false,
+			retryAfterParamsExpected:        nil,
+		},
+		{
+			name: "shutdown-send-retry-after is enabled, the apserver is shutting down",
+			config: func() *Config {
+				c := &Config{
+					lifecycleSignals:                newLifecycleSignals(),
+					StartupSendRetryAfterUntilReady: false,
+					ShutdownSendRetryAfter:          true,
+				}
+				c.lifecycleSignals.HasBeenReady.Signal()
+				c.lifecycleSignals.AfterShutdownDelayDuration.Signal()
+				return c
+			}(),
+			addWithRetryAfterFilterExpected: true,
+			sendRetryAfterExpected:          true,
+			retryAfterParamsExpected: &genericfilters.RetryAfterParams{
+				TearDownConnection: true,
+				Message:            "The apiserver is shutting down, please try again later.",
+			},
+		},
+		{
+			name: "shutdown-send-retry-after is enabled, the apserver is not in shutdown mode",
+			config: &Config{
+				lifecycleSignals:                newLifecycleSignals(),
+				StartupSendRetryAfterUntilReady: false,
+				ShutdownSendRetryAfter:          true,
+			},
+			addWithRetryAfterFilterExpected: true,
+			sendRetryAfterExpected:          false,
+			retryAfterParamsExpected:        nil,
+		},
+		{
+			name: "startup-send-retry-after-until-ready is enabled, the apserver is not ready yet",
+			config: &Config{
+				lifecycleSignals:                newLifecycleSignals(),
+				StartupSendRetryAfterUntilReady: true,
+				ShutdownSendRetryAfter:          false,
+			},
+			addWithRetryAfterFilterExpected: true,
+			sendRetryAfterExpected:          true,
+			retryAfterParamsExpected: &genericfilters.RetryAfterParams{
+				TearDownConnection: false,
+				Message:            "The apiserver hasn't been fully initialized yet, please try again later.",
+			},
+		},
+		{
+			name: "startup-send-retry-after-until-ready is enabled, the apserver is ready",
+			config: func() *Config {
+				c := &Config{
+					lifecycleSignals:                newLifecycleSignals(),
+					StartupSendRetryAfterUntilReady: true,
+					ShutdownSendRetryAfter:          false,
+				}
+				c.lifecycleSignals.HasBeenReady.Signal()
+				return c
+			}(),
+			addWithRetryAfterFilterExpected: true,
+			sendRetryAfterExpected:          false,
+			retryAfterParamsExpected:        nil,
+		},
+		{
+			name: "both shutdown-send-retry-after is enabled and startup-send-retry-after-until-ready are enabled, the apserver is not ready",
+			config: &Config{
+				lifecycleSignals:                newLifecycleSignals(),
+				StartupSendRetryAfterUntilReady: true,
+				ShutdownSendRetryAfter:          true,
+			},
+			addWithRetryAfterFilterExpected: true,
+			sendRetryAfterExpected:          true,
+			retryAfterParamsExpected: &genericfilters.RetryAfterParams{
+				TearDownConnection: false,
+				Message:            "The apiserver hasn't been fully initialized yet, please try again later.",
+			},
+		},
+		{
+			name: "both shutdown-send-retry-after is enabled and startup-send-retry-after-until-ready are enabled, the apserver is ready",
+			config: func() *Config {
+				c := &Config{
+					lifecycleSignals:                newLifecycleSignals(),
+					StartupSendRetryAfterUntilReady: true,
+					ShutdownSendRetryAfter:          true,
+				}
+				c.lifecycleSignals.HasBeenReady.Signal()
+				return c
+			}(),
+			addWithRetryAfterFilterExpected: true,
+			sendRetryAfterExpected:          false,
+			retryAfterParamsExpected:        nil,
+		},
+		{
+			name: "both shutdown-send-retry-after is enabled and startup-send-retry-after-until-ready are enabled, the apserver is shutting down",
+			config: func() *Config {
+				c := &Config{
+					lifecycleSignals:                newLifecycleSignals(),
+					StartupSendRetryAfterUntilReady: true,
+					ShutdownSendRetryAfter:          true,
+				}
+				c.lifecycleSignals.HasBeenReady.Signal()
+				c.lifecycleSignals.AfterShutdownDelayDuration.Signal()
+				return c
+			}(),
+			addWithRetryAfterFilterExpected: true,
+			sendRetryAfterExpected:          true,
+			retryAfterParamsExpected: &genericfilters.RetryAfterParams{
+				TearDownConnection: true,
+				Message:            "The apiserver is shutting down, please try again later.",
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			shouldRespondWithRetryAfterFn := test.config.shouldAddWithRetryAfterFilter()
+
+			// we need to sleep some time to allow the goroutine launched by
+			// shouldAddWithRetryAfterFilter to finish
+			time.Sleep(100 * time.Millisecond)
+
+			if test.addWithRetryAfterFilterExpected != (shouldRespondWithRetryAfterFn != nil) {
+				t.Errorf("Expected add WithRetryAfter: %t, but got: %t", test.addWithRetryAfterFilterExpected, shouldRespondWithRetryAfterFn != nil)
+			}
+			if !test.addWithRetryAfterFilterExpected {
+				return
+			}
+
+			paramsGot, sendRetryAfterGot := shouldRespondWithRetryAfterFn()
+			if test.sendRetryAfterExpected != sendRetryAfterGot {
+				t.Errorf("Expected send retry-after: %t, but got: %t", test.sendRetryAfterExpected, sendRetryAfterGot)
+			}
+			if !reflect.DeepEqual(test.retryAfterParamsExpected, paramsGot) {
+				t.Errorf("Expected retry-after params to match, diff: %s", cmp.Diff(test.retryAfterParamsExpected, paramsGot))
+			}
+		})
+	}
+}
+
 type testBackend struct {
 	events []*auditinternal.Event
 

staging/src/k8s.io/apiserver/pkg/server/filters/with_retry_after.go

@@ -36,8 +36,8 @@ var (
 // with a Retry-After response, otherwise it returns false.
 type isRequestExemptFunc func(*http.Request) bool
 
-// retryAfterParams dictates how the Retry-After response is constructed
-type retryAfterParams struct {
+// RetryAfterParams dictates how the Retry-After response is constructed
+type RetryAfterParams struct {
 	// TearDownConnection is true when we should send a 'Connection: close'
 	// header in the response so net/http can tear down the TCP connection.
 	TearDownConnection bool
@@ -46,11 +46,11 @@ type retryAfterParams struct {
 	Message string
 }
 
-// shouldRespondWithRetryAfterFunc returns true if the requests should
+// ShouldRespondWithRetryAfterFunc returns true if the requests should
 // be rejected with a Retry-After response once certain conditions are met.
-// The retryAfterParams returned contains instructions on how to
+// The RetryAfterParams returned contains instructions on how to
 // construct the Retry-After response.
-type shouldRespondWithRetryAfterFunc func() (*retryAfterParams, bool)
+type ShouldRespondWithRetryAfterFunc func() (*RetryAfterParams, bool)
 
 // WithRetryAfter rejects any incoming new request(s) with a 429
 // if the specified shutdownDelayDurationElapsedFn channel is closed
@@ -62,25 +62,13 @@ type shouldRespondWithRetryAfterFunc func() (*retryAfterParams, bool)
 //   - 'Connection: close': tear down the TCP connection
 //
 // TODO: is there a way to merge WithWaitGroup and this filter?
-func WithRetryAfter(handler http.Handler, shutdownDelayDurationElapsedCh <-chan struct{}) http.Handler {
-	shutdownRetryAfterParams := &retryAfterParams{
-		TearDownConnection: true,
-		Message:            "The apiserver is shutting down, please try again later.",
-	}
-
+func WithRetryAfter(handler http.Handler, when ShouldRespondWithRetryAfterFunc) http.Handler {
 	// NOTE: both WithRetryAfter and WithWaitGroup must use the same exact isRequestExemptFunc 'isRequestExemptFromRetryAfter,
 	// otherwise SafeWaitGroup might wait indefinitely and will prevent the server from shutting down gracefully.
-	return withRetryAfter(handler, isRequestExemptFromRetryAfter, func() (*retryAfterParams, bool) {
-		select {
-		case <-shutdownDelayDurationElapsedCh:
-			return shutdownRetryAfterParams, true
-		default:
-			return nil, false
-		}
-	})
+	return withRetryAfter(handler, isRequestExemptFromRetryAfter, when)
 }
 
-func withRetryAfter(handler http.Handler, isRequestExemptFn isRequestExemptFunc, shouldRespondWithRetryAfterFn shouldRespondWithRetryAfterFunc) http.Handler {
+func withRetryAfter(handler http.Handler, isRequestExemptFn isRequestExemptFunc, shouldRespondWithRetryAfterFn ShouldRespondWithRetryAfterFunc) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
 		params, send := shouldRespondWithRetryAfterFn()
 		if !send || isRequestExemptFn(req) {

staging/src/k8s.io/apiserver/pkg/server/filters/with_retry_after_test.go

@@ -27,20 +27,20 @@ import (
 
 func TestWithRetryAfter(t *testing.T) {
 	tests := []struct {
-		name                           string
-		shutdownDelayDurationElapsedFn func() <-chan struct{}
-		requestURL                     string
-		userAgent                      string
-		safeWaitGroupIsWaiting         bool
-		handlerInvoked                 int
-		closeExpected                  string
-		retryAfterExpected             string
-		statusCodeExpected             int
+		name                   string
+		when                   ShouldRespondWithRetryAfterFunc
+		requestURL             string
+		userAgent              string
+		safeWaitGroupIsWaiting bool
+		handlerInvoked         int
+		closeExpected          string
+		retryAfterExpected     string
+		statusCodeExpected     int
 	}{
 		{
 			name: "retry-after disabled",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(false)
+			when: func() (*RetryAfterParams, bool) {
+				return nil, false
 			},
 			requestURL:         "/api/v1/namespaces",
 			userAgent:          "foo",
@@ -51,8 +51,11 @@ func TestWithRetryAfter(t *testing.T) {
 		},
 		{
 			name: "retry-after enabled, request is not exempt",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(true)
+			when: func() (*RetryAfterParams, bool) {
+				return &RetryAfterParams{
+					TearDownConnection: true,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
 			},
 			requestURL:         "/api/v1/namespaces",
 			userAgent:          "foo",
@@ -61,10 +64,28 @@ func TestWithRetryAfter(t *testing.T) {
 			retryAfterExpected: "5",
 			statusCodeExpected: http.StatusTooManyRequests,
 		},
+		{
+			name: "retry-after enabled, request is not exempt, no connection tear down",
+			when: func() (*RetryAfterParams, bool) {
+				return &RetryAfterParams{
+					TearDownConnection: false,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
+			},
+			requestURL:         "/api/v1/namespaces",
+			userAgent:          "foo",
+			handlerInvoked:     0,
+			closeExpected:      "",
+			retryAfterExpected: "5",
+			statusCodeExpected: http.StatusTooManyRequests,
+		},
 		{
 			name: "retry-after enabled, request is exempt(/metrics)",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(true)
+			when: func() (*RetryAfterParams, bool) {
+				return &RetryAfterParams{
+					TearDownConnection: true,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
 			},
 			requestURL:         "/metrics?foo=bar",
 			userAgent:          "foo",
@@ -75,8 +96,11 @@ func TestWithRetryAfter(t *testing.T) {
 		},
 		{
 			name: "retry-after enabled, request is exempt(/livez)",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(true)
+			when: func() (*RetryAfterParams, bool) {
+				return &RetryAfterParams{
+					TearDownConnection: true,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
 			},
 			requestURL:         "/livez?verbose",
 			userAgent:          "foo",
@@ -87,8 +111,11 @@ func TestWithRetryAfter(t *testing.T) {
 		},
 		{
 			name: "retry-after enabled, request is exempt(/readyz)",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(true)
+			when: func() (*RetryAfterParams, bool) {
+				return &RetryAfterParams{
+					TearDownConnection: true,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
 			},
 			requestURL:         "/readyz?verbose",
 			userAgent:          "foo",
@@ -99,8 +126,11 @@ func TestWithRetryAfter(t *testing.T) {
 		},
 		{
 			name: "retry-after enabled, request is exempt(/healthz)",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(true)
+			when: func() (*RetryAfterParams, bool) {
+				return &RetryAfterParams{
+					TearDownConnection: true,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
 			},
 			requestURL:         "/healthz?verbose",
 			userAgent:          "foo",
@@ -111,8 +141,11 @@ func TestWithRetryAfter(t *testing.T) {
 		},
 		{
 			name: "retry-after enabled, request is exempt(local loopback)",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(true)
+			when: func() (*RetryAfterParams, bool) {
+				return &RetryAfterParams{
+					TearDownConnection: true,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
 			},
 			requestURL:         "/api/v1/namespaces",
 			userAgent:          "kube-apiserver/",
@@ -121,22 +154,13 @@ func TestWithRetryAfter(t *testing.T) {
 			retryAfterExpected: "",
 			statusCodeExpected: http.StatusOK,
 		},
-		{
-			name: "nil channel",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return nil
-			},
-			requestURL:         "/api/v1/namespaces",
-			userAgent:          "foo",
-			handlerInvoked:     1,
-			closeExpected:      "",
-			retryAfterExpected: "",
-			statusCodeExpected: http.StatusOK,
-		},
 		{
 			name: "retry-after enabled, request is exempt(/readyz), SafeWaitGroup is in waiting mode",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(true)
+			when: func() (*RetryAfterParams, bool) {
+				return &RetryAfterParams{
+					TearDownConnection: true,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
 			},
 			requestURL:             "/readyz?verbose",
 			userAgent:              "foo",
@@ -165,7 +189,7 @@ func TestWithRetryAfter(t *testing.T) {
 			wrapped := WithWaitGroup(handler, func(*http.Request, *apirequest.RequestInfo) bool {
 				return false
 			}, safeWG)
-			wrapped = WithRetryAfter(wrapped, test.shutdownDelayDurationElapsedFn())
+			wrapped = WithRetryAfter(wrapped, test.when)
 
 			req, err := http.NewRequest(http.MethodGet, test.requestURL, nil)
 			if err != nil {
@@ -197,11 +221,3 @@ func TestWithRetryAfter(t *testing.T) {
 		})
 	}
 }
-
-func newChannel(closed bool) <-chan struct{} {
-	ch := make(chan struct{})
-	if closed {
-		close(ch)
-	}
-	return ch
-}

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

@@ -518,8 +518,8 @@ func newGenericAPIServer(t *testing.T, keepListening bool) *GenericAPIServer {
 	config.ShutdownSendRetryAfter = keepListening
 	config.BuildHandlerChainFunc = func(apiHandler http.Handler, c *Config) http.Handler {
 		handler := genericfilters.WithWaitGroup(apiHandler, c.LongRunningFunc, c.HandlerChainWaitGroup)
-		if c.ShutdownSendRetryAfter {
-			handler = genericfilters.WithRetryAfter(handler, c.lifecycleSignals.AfterShutdownDelayDuration.Signaled())
+		if shouldRetryAfterFn := c.shouldAddWithRetryAfterFilter(); shouldRetryAfterFn != nil {
+			handler = genericfilters.WithRetryAfter(handler, shouldRetryAfterFn)
 		}
 		handler = genericapifilters.WithRequestInfo(handler, c.RequestInfoResolver)
 		return handler

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

@@ -63,21 +63,31 @@ type ServerRunOptions struct {
 	// If enabled, after ShutdownDelayDuration elapses, any incoming request is
 	// rejected with a 429 status code and a 'Retry-After' response.
 	ShutdownSendRetryAfter bool
+
+	// StartupSendRetryAfterUntilReady once set will reject incoming requests with
+	// a 429 status code and a 'Retry-After' response header until the apiserver
+	// hasn't fully initialized.
+	// This option ensures that the system stays consistent even when requests
+	// are received before the server has been initialized.
+	// In particular, it prevents child deletion in case of GC or/and orphaned
+	// content in case of the namespaces controller.
+	StartupSendRetryAfterUntilReady bool
 }
 
 func NewServerRunOptions() *ServerRunOptions {
 	defaults := server.NewConfig(serializer.CodecFactory{})
 	return &ServerRunOptions{
-		MaxRequestsInFlight:         defaults.MaxRequestsInFlight,
-		MaxMutatingRequestsInFlight: defaults.MaxMutatingRequestsInFlight,
-		RequestTimeout:              defaults.RequestTimeout,
-		LivezGracePeriod:            defaults.LivezGracePeriod,
-		MinRequestTimeout:           defaults.MinRequestTimeout,
-		ShutdownDelayDuration:       defaults.ShutdownDelayDuration,
-		JSONPatchMaxCopyBytes:       defaults.JSONPatchMaxCopyBytes,
-		MaxRequestBodyBytes:         defaults.MaxRequestBodyBytes,
-		EnablePriorityAndFairness:   true,
-		ShutdownSendRetryAfter:      false,
+		MaxRequestsInFlight:             defaults.MaxRequestsInFlight,
+		MaxMutatingRequestsInFlight:     defaults.MaxMutatingRequestsInFlight,
+		RequestTimeout:                  defaults.RequestTimeout,
+		LivezGracePeriod:                defaults.LivezGracePeriod,
+		MinRequestTimeout:               defaults.MinRequestTimeout,
+		ShutdownDelayDuration:           defaults.ShutdownDelayDuration,
+		JSONPatchMaxCopyBytes:           defaults.JSONPatchMaxCopyBytes,
+		MaxRequestBodyBytes:             defaults.MaxRequestBodyBytes,
+		EnablePriorityAndFairness:       true,
+		ShutdownSendRetryAfter:          false,
+		StartupSendRetryAfterUntilReady: false,
 	}
 }
 
@@ -97,6 +107,7 @@ func (s *ServerRunOptions) ApplyTo(c *server.Config) error {
 	c.MaxRequestBodyBytes = s.MaxRequestBodyBytes
 	c.PublicAddress = s.AdvertiseAddress
 	c.ShutdownSendRetryAfter = s.ShutdownSendRetryAfter
+	c.StartupSendRetryAfterUntilReady = s.StartupSendRetryAfterUntilReady
 
 	return nil
 }
@@ -261,5 +272,10 @@ func (s *ServerRunOptions) AddUniversalFlags(fs *pflag.FlagSet) {
 		"during this window all incoming requests will be rejected with a status code 429 and a 'Retry-After' response header, "+
 		"in addition 'Connection: close' response header is set in order to tear down the TCP connection when idle.")
 
+	fs.BoolVar(&s.StartupSendRetryAfterUntilReady, "startup-send-retry-after-until-ready", s.ShutdownSendRetryAfter, ""+
+		"If true, incoming request(s) will be rejected with a '429' status code and a 'Retry-After' response header "+
+		"until the apiserver has initialized. This option ensures that the system stays consistent even when requests "+
+		"arrive at the server before it has been initialized.")
+
 	utilfeature.DefaultMutableFeatureGate.AddFlag(fs)
 }