ceph-csi/vendor/k8s.io/apiserver/pkg/server/genericapiserver.go

/*
Copyright 2014 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"
	"net/http"
	gpath "path"
	"strings"
	"sync"
	"time"

	systemd "github.com/coreos/go-systemd/v22/daemon"

	"golang.org/x/time/rate"
	apidiscoveryv2beta1 "k8s.io/api/apidiscovery/v2beta1"
	"k8s.io/apimachinery/pkg/api/meta"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/apimachinery/pkg/runtime/serializer"
	"k8s.io/apimachinery/pkg/util/managedfields"
	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
	"k8s.io/apimachinery/pkg/util/sets"
	utilwaitgroup "k8s.io/apimachinery/pkg/util/waitgroup"
	"k8s.io/apimachinery/pkg/version"
	"k8s.io/apiserver/pkg/admission"
	"k8s.io/apiserver/pkg/audit"
	"k8s.io/apiserver/pkg/authorization/authorizer"
	genericapi "k8s.io/apiserver/pkg/endpoints"
	"k8s.io/apiserver/pkg/endpoints/discovery"
	discoveryendpoint "k8s.io/apiserver/pkg/endpoints/discovery/aggregated"
	"k8s.io/apiserver/pkg/features"
	"k8s.io/apiserver/pkg/registry/rest"
	"k8s.io/apiserver/pkg/server/healthz"
	"k8s.io/apiserver/pkg/server/routes"
	"k8s.io/apiserver/pkg/storageversion"
	utilfeature "k8s.io/apiserver/pkg/util/feature"
	restclient "k8s.io/client-go/rest"
	"k8s.io/klog/v2"
	openapibuilder3 "k8s.io/kube-openapi/pkg/builder3"
	openapicommon "k8s.io/kube-openapi/pkg/common"
	"k8s.io/kube-openapi/pkg/handler"
	"k8s.io/kube-openapi/pkg/handler3"
	openapiutil "k8s.io/kube-openapi/pkg/util"
	"k8s.io/kube-openapi/pkg/validation/spec"
	"k8s.io/utils/clock"
)

// Info about an API group.
type APIGroupInfo struct {
	PrioritizedVersions []schema.GroupVersion
	// Info about the resources in this group. It's a map from version to resource to the storage.
	VersionedResourcesStorageMap map[string]map[string]rest.Storage
	// OptionsExternalVersion controls the APIVersion used for common objects in the
	// schema like api.Status, api.DeleteOptions, and metav1.ListOptions. Other implementors may
	// define a version "v1beta1" but want to use the Kubernetes "v1" internal objects.
	// If nil, defaults to groupMeta.GroupVersion.
	// TODO: Remove this when https://github.com/kubernetes/kubernetes/issues/19018 is fixed.
	OptionsExternalVersion *schema.GroupVersion
	// MetaGroupVersion defaults to "meta.k8s.io/v1" and is the scheme group version used to decode
	// common API implementations like ListOptions. Future changes will allow this to vary by group
	// version (for when the inevitable meta/v2 group emerges).
	MetaGroupVersion *schema.GroupVersion

	// Scheme includes all of the types used by this group and how to convert between them (or
	// to convert objects from outside of this group that are accepted in this API).
	// TODO: replace with interfaces
	Scheme *runtime.Scheme
	// NegotiatedSerializer controls how this group encodes and decodes data
	NegotiatedSerializer runtime.NegotiatedSerializer
	// ParameterCodec performs conversions for query parameters passed to API calls
	ParameterCodec runtime.ParameterCodec

	// StaticOpenAPISpec is the spec derived from the definitions of all resources installed together.
	// It is set during InstallAPIGroups, InstallAPIGroup, and InstallLegacyAPIGroup.
	StaticOpenAPISpec map[string]*spec.Schema
}

func (a *APIGroupInfo) destroyStorage() {
	for _, stores := range a.VersionedResourcesStorageMap {
		for _, store := range stores {
			store.Destroy()
		}
	}
}

// GenericAPIServer contains state for a Kubernetes cluster api server.
type GenericAPIServer struct {
	// discoveryAddresses is used to build cluster IPs for discovery.
	discoveryAddresses discovery.Addresses

	// LoopbackClientConfig is a config for a privileged loopback connection to the API server
	LoopbackClientConfig *restclient.Config

	// minRequestTimeout is how short the request timeout can be.  This is used to build the RESTHandler
	minRequestTimeout time.Duration

	// ShutdownTimeout is the timeout used for server shutdown. This specifies the timeout before server
	// gracefully shutdown returns.
	ShutdownTimeout time.Duration

	// legacyAPIGroupPrefixes is used to set up URL parsing for authorization and for validating requests
	// to InstallLegacyAPIGroup
	legacyAPIGroupPrefixes sets.String

	// admissionControl is used to build the RESTStorage that backs an API Group.
	admissionControl admission.Interface

	// SecureServingInfo holds configuration of the TLS server.
	SecureServingInfo *SecureServingInfo

	// ExternalAddress is the address (hostname or IP and port) that should be used in
	// external (public internet) URLs for this GenericAPIServer.
	ExternalAddress string

	// Serializer controls how common API objects not in a group/version prefix are serialized for this server.
	// Individual APIGroups may define their own serializers.
	Serializer runtime.NegotiatedSerializer

	// "Outputs"
	// Handler holds the handlers being used by this API server
	Handler *APIServerHandler

	// UnprotectedDebugSocket is used to serve pprof information in a unix-domain socket. This socket is
	// not protected by authentication/authorization.
	UnprotectedDebugSocket *routes.DebugSocket

	// listedPathProvider is a lister which provides the set of paths to show at /
	listedPathProvider routes.ListedPathProvider

	// DiscoveryGroupManager serves /apis in an unaggregated form.
	DiscoveryGroupManager discovery.GroupManager

	// AggregatedDiscoveryGroupManager serves /apis in an aggregated form.
	AggregatedDiscoveryGroupManager discoveryendpoint.ResourceManager

	// AggregatedLegacyDiscoveryGroupManager serves /api in an aggregated form.
	AggregatedLegacyDiscoveryGroupManager discoveryendpoint.ResourceManager

	// Enable swagger and/or OpenAPI if these configs are non-nil.
	openAPIConfig *openapicommon.Config

	// Enable swagger and/or OpenAPI V3 if these configs are non-nil.
	openAPIV3Config *openapicommon.Config

	// SkipOpenAPIInstallation indicates not to install the OpenAPI handler
	// during PrepareRun.
	// Set this to true when the specific API Server has its own OpenAPI handler
	// (e.g. kube-aggregator)
	skipOpenAPIInstallation bool

	// OpenAPIVersionedService controls the /openapi/v2 endpoint, and can be used to update the served spec.
	// It is set during PrepareRun if `openAPIConfig` is non-nil unless `skipOpenAPIInstallation` is true.
	OpenAPIVersionedService *handler.OpenAPIService

	// OpenAPIV3VersionedService controls the /openapi/v3 endpoint and can be used to update the served spec.
	// It is set during PrepareRun if `openAPIConfig` is non-nil unless `skipOpenAPIInstallation` is true.
	OpenAPIV3VersionedService *handler3.OpenAPIService

	// StaticOpenAPISpec is the spec derived from the restful container endpoints.
	// It is set during PrepareRun.
	StaticOpenAPISpec *spec.Swagger

	// PostStartHooks are each called after the server has started listening, in a separate go func for each
	// with no guarantee of ordering between them.  The map key is a name used for error reporting.
	// It may kill the process with a panic if it wishes to by returning an error.
	postStartHookLock      sync.Mutex
	postStartHooks         map[string]postStartHookEntry
	postStartHooksCalled   bool
	disabledPostStartHooks sets.String

	preShutdownHookLock    sync.Mutex
	preShutdownHooks       map[string]preShutdownHookEntry
	preShutdownHooksCalled bool

	// healthz checks
	healthzLock            sync.Mutex
	healthzChecks          []healthz.HealthChecker
	healthzChecksInstalled bool
	// livez checks
	livezLock            sync.Mutex
	livezChecks          []healthz.HealthChecker
	livezChecksInstalled bool
	// readyz checks
	readyzLock            sync.Mutex
	readyzChecks          []healthz.HealthChecker
	readyzChecksInstalled bool
	livezGracePeriod      time.Duration
	livezClock            clock.Clock

	// auditing. The backend is started before the server starts listening.
	AuditBackend audit.Backend

	// Authorizer determines whether a user is allowed to make a certain request. The Handler does a preliminary
	// authorization check using the request URI but it may be necessary to make additional checks, such as in
	// the create-on-update case
	Authorizer authorizer.Authorizer

	// EquivalentResourceRegistry provides information about resources equivalent to a given resource,
	// and the kind associated with a given resource. As resources are installed, they are registered here.
	EquivalentResourceRegistry runtime.EquivalentResourceRegistry

	// delegationTarget is the next delegate in the chain. This is never nil.
	delegationTarget DelegationTarget

	// NonLongRunningRequestWaitGroup allows you to wait for all chain
	// handlers associated with non long-running requests
	// to complete while the server is shuting down.
	NonLongRunningRequestWaitGroup *utilwaitgroup.SafeWaitGroup
	// WatchRequestWaitGroup allows us to wait for all chain
	// handlers associated with active watch requests to
	// complete while the server is shuting down.
	WatchRequestWaitGroup *utilwaitgroup.RateLimitedSafeWaitGroup

	// ShutdownDelayDuration allows to block shutdown for some time, e.g. until endpoints pointing to this API server
	// have converged on all node. During this time, the API server keeps serving, /healthz will return 200,
	// but /readyz will return failure.
	ShutdownDelayDuration time.Duration

	// The limit on the request body size that would be accepted and decoded in a write request.
	// 0 means no limit.
	maxRequestBodyBytes int64

	// APIServerID is the ID of this API server
	APIServerID string

	// StorageVersionManager holds the storage versions of the API resources installed by this server.
	StorageVersionManager storageversion.Manager

	// Version will enable the /version endpoint if non-nil
	Version *version.Info

	// lifecycleSignals provides access to the various signals that happen during the life cycle of the apiserver.
	lifecycleSignals lifecycleSignals

	// destroyFns contains a list of functions that should be called on shutdown to clean up resources.
	destroyFns []func()

	// muxAndDiscoveryCompleteSignals holds signals that indicate all known HTTP paths have been registered.
	// it exists primarily to avoid returning a 404 response when a resource actually exists but we haven't installed the path to a handler.
	// it is exposed for easier composition of the individual servers.
	// the primary users of this field are the WithMuxCompleteProtection filter and the NotFoundHandler
	muxAndDiscoveryCompleteSignals map[string]<-chan struct{}

	// ShutdownSendRetryAfter dictates when to initiate shutdown of the HTTP
	// Server during the graceful termination of the apiserver. If true, we wait
	// for non longrunning requests in flight to be drained and then initiate a
	// shutdown of the HTTP Server. If false, we initiate a shutdown of the HTTP
	// Server as soon as ShutdownDelayDuration has elapsed.
	// If enabled, after ShutdownDelayDuration elapses, any incoming request is
	// rejected with a 429 status code and a 'Retry-After' response.
	ShutdownSendRetryAfter bool

	// ShutdownWatchTerminationGracePeriod, if set to a positive value,
	// is the maximum duration the apiserver will wait for all active
	// watch request(s) to drain.
	// Once this grace period elapses, the apiserver will no longer
	// wait for any active watch request(s) in flight to drain, it will
	// proceed to the next step in the graceful server shutdown process.
	// If set to a positive value, the apiserver will keep track of the
	// number of active watch request(s) in flight and during shutdown
	// it will wait, at most, for the specified duration and allow these
	// active watch requests to drain with some rate limiting in effect.
	// The default is zero, which implies the apiserver will not keep
	// track of active watch request(s) in flight and will not wait
	// for them to drain, this maintains backward compatibility.
	// This grace period is orthogonal to other grace periods, and
	// it is not overridden by any other grace period.
	ShutdownWatchTerminationGracePeriod time.Duration
}

// DelegationTarget is an interface which allows for composition of API servers with top level handling that works
// as expected.
type DelegationTarget interface {
	// UnprotectedHandler returns a handler that is NOT protected by a normal chain
	UnprotectedHandler() http.Handler

	// PostStartHooks returns the post-start hooks that need to be combined
	PostStartHooks() map[string]postStartHookEntry

	// PreShutdownHooks returns the pre-stop hooks that need to be combined
	PreShutdownHooks() map[string]preShutdownHookEntry

	// HealthzChecks returns the healthz checks that need to be combined
	HealthzChecks() []healthz.HealthChecker

	// ListedPaths returns the paths for supporting an index
	ListedPaths() []string

	// NextDelegate returns the next delegationTarget in the chain of delegations
	NextDelegate() DelegationTarget

	// PrepareRun does post API installation setup steps. It calls recursively the same function of the delegates.
	PrepareRun() preparedGenericAPIServer

	// MuxAndDiscoveryCompleteSignals exposes registered signals that indicate if all known HTTP paths have been installed.
	MuxAndDiscoveryCompleteSignals() map[string]<-chan struct{}

	// Destroy cleans up its resources on shutdown.
	// Destroy has to be implemented in thread-safe way and be prepared
	// for being called more than once.
	Destroy()
}

func (s *GenericAPIServer) UnprotectedHandler() http.Handler {
	// when we delegate, we need the server we're delegating to choose whether or not to use gorestful
	return s.Handler.Director
}
func (s *GenericAPIServer) PostStartHooks() map[string]postStartHookEntry {
	return s.postStartHooks
}
func (s *GenericAPIServer) PreShutdownHooks() map[string]preShutdownHookEntry {
	return s.preShutdownHooks
}
func (s *GenericAPIServer) HealthzChecks() []healthz.HealthChecker {
	return s.healthzChecks
}
func (s *GenericAPIServer) ListedPaths() []string {
	return s.listedPathProvider.ListedPaths()
}

func (s *GenericAPIServer) NextDelegate() DelegationTarget {
	return s.delegationTarget
}

// RegisterMuxAndDiscoveryCompleteSignal registers the given signal that will be used to determine if all known
// HTTP paths have been registered. It is okay to call this method after instantiating the generic server but before running.
func (s *GenericAPIServer) RegisterMuxAndDiscoveryCompleteSignal(signalName string, signal <-chan struct{}) error {
	if _, exists := s.muxAndDiscoveryCompleteSignals[signalName]; exists {
		return fmt.Errorf("%s already registered", signalName)
	}
	s.muxAndDiscoveryCompleteSignals[signalName] = signal
	return nil
}

func (s *GenericAPIServer) MuxAndDiscoveryCompleteSignals() map[string]<-chan struct{} {
	return s.muxAndDiscoveryCompleteSignals
}

// RegisterDestroyFunc registers a function that will be called during Destroy().
// The function have to be idempotent and prepared to be called more than once.
func (s *GenericAPIServer) RegisterDestroyFunc(destroyFn func()) {
	s.destroyFns = append(s.destroyFns, destroyFn)
}

// Destroy cleans up all its and its delegation target resources on shutdown.
// It starts with destroying its own resources and later proceeds with
// its delegation target.
func (s *GenericAPIServer) Destroy() {
	for _, destroyFn := range s.destroyFns {
		destroyFn()
	}
	if s.delegationTarget != nil {
		s.delegationTarget.Destroy()
	}
}

type emptyDelegate struct {
	// handler is called at the end of the delegation chain
	// when a request has been made against an unregistered HTTP path the individual servers will simply pass it through until it reaches the handler.
	handler http.Handler
}

func NewEmptyDelegate() DelegationTarget {
	return emptyDelegate{}
}

// NewEmptyDelegateWithCustomHandler allows for registering a custom handler usually for special handling of 404 requests
func NewEmptyDelegateWithCustomHandler(handler http.Handler) DelegationTarget {
	return emptyDelegate{handler}
}

func (s emptyDelegate) UnprotectedHandler() http.Handler {
	return s.handler
}
func (s emptyDelegate) PostStartHooks() map[string]postStartHookEntry {
	return map[string]postStartHookEntry{}
}
func (s emptyDelegate) PreShutdownHooks() map[string]preShutdownHookEntry {
	return map[string]preShutdownHookEntry{}
}
func (s emptyDelegate) HealthzChecks() []healthz.HealthChecker {
	return []healthz.HealthChecker{}
}
func (s emptyDelegate) ListedPaths() []string {
	return []string{}
}
func (s emptyDelegate) NextDelegate() DelegationTarget {
	return nil
}
func (s emptyDelegate) PrepareRun() preparedGenericAPIServer {
	return preparedGenericAPIServer{nil}
}
func (s emptyDelegate) MuxAndDiscoveryCompleteSignals() map[string]<-chan struct{} {
	return map[string]<-chan struct{}{}
}
func (s emptyDelegate) Destroy() {
}

// preparedGenericAPIServer is a private wrapper that enforces a call of PrepareRun() before Run can be invoked.
type preparedGenericAPIServer struct {
	*GenericAPIServer
}

// PrepareRun does post API installation setup steps. It calls recursively the same function of the delegates.
func (s *GenericAPIServer) PrepareRun() preparedGenericAPIServer {
	s.delegationTarget.PrepareRun()

	if s.openAPIConfig != nil && !s.skipOpenAPIInstallation {
		s.OpenAPIVersionedService, s.StaticOpenAPISpec = routes.OpenAPI{
			Config: s.openAPIConfig,
		}.InstallV2(s.Handler.GoRestfulContainer, s.Handler.NonGoRestfulMux)
	}

	if s.openAPIV3Config != nil && !s.skipOpenAPIInstallation {
		if utilfeature.DefaultFeatureGate.Enabled(features.OpenAPIV3) {
			s.OpenAPIV3VersionedService = routes.OpenAPI{
				Config: s.openAPIV3Config,
			}.InstallV3(s.Handler.GoRestfulContainer, s.Handler.NonGoRestfulMux)
		}
	}

	s.installHealthz()
	s.installLivez()

	// as soon as shutdown is initiated, readiness should start failing
	readinessStopCh := s.lifecycleSignals.ShutdownInitiated.Signaled()
	err := s.addReadyzShutdownCheck(readinessStopCh)
	if err != nil {
		klog.Errorf("Failed to install readyz shutdown check %s", err)
	}
	s.installReadyz()

	return preparedGenericAPIServer{s}
}

// Run spawns the secure http server. It only returns if stopCh is closed
// or the secure port cannot be listened on initially.
// This is the diagram of what channels/signals are dependent on each other:
//
// |                                  stopCh
// |                                    |
// |           ---------------------------------------------------------
// |           |                                                       |
// |    ShutdownInitiated (shutdownInitiatedCh)                        |
// |           |                                                       |
// | (ShutdownDelayDuration)                                    (PreShutdownHooks)
// |           |                                                       |
// |  AfterShutdownDelayDuration (delayedStopCh)   PreShutdownHooksStopped (preShutdownHooksHasStoppedCh)
// |           |                                                       |
// |           |-------------------------------------------------------|
// |                                    |
// |                                    |
// |               NotAcceptingNewRequest (notAcceptingNewRequestCh)
// |                                    |
// |                                    |
// |           |----------------------------------------------------------------------------------|
// |           |                        |              |                                          |
// |        [without                 [with             |                                          |
// | ShutdownSendRetryAfter]  ShutdownSendRetryAfter]  |                                          |
// |           |                        |              |                                          |
// |           |                        ---------------|                                          |
// |           |                                       |                                          |
// |           |                      |----------------|-----------------------|                  |
// |           |                      |                                        |                  |
// |           |         (NonLongRunningRequestWaitGroup::Wait)   (WatchRequestWaitGroup::Wait)   |
// |           |                      |                                        |                  |
// |           |                      |------------------|---------------------|                  |
// |           |                                         |                                        |
// |           |                         InFlightRequestsDrained (drainedCh)                      |
// |           |                                         |                                        |
// |           |-------------------|---------------------|----------------------------------------|
// |                               |                     |
// |                       stopHttpServerCh     (AuditBackend::Shutdown())
// |                               |
// |                       listenerStoppedCh
// |                               |
// |      HTTPServerStoppedListening (httpServerStoppedListeningCh)
func (s preparedGenericAPIServer) Run(stopCh <-chan struct{}) error {
	delayedStopCh := s.lifecycleSignals.AfterShutdownDelayDuration
	shutdownInitiatedCh := s.lifecycleSignals.ShutdownInitiated

	// Clean up resources on shutdown.
	defer s.Destroy()

	// If UDS profiling is enabled, start a local http server listening on that socket
	if s.UnprotectedDebugSocket != nil {
		go func() {
			defer utilruntime.HandleCrash()
			klog.Error(s.UnprotectedDebugSocket.Run(stopCh))
		}()
	}

	// spawn a new goroutine for closing the MuxAndDiscoveryComplete signal
	// registration happens during construction of the generic api server
	// the last server in the chain aggregates signals from the previous instances
	go func() {
		for _, muxAndDiscoveryCompletedSignal := range s.GenericAPIServer.MuxAndDiscoveryCompleteSignals() {
			select {
			case <-muxAndDiscoveryCompletedSignal:
				continue
			case <-stopCh:
				klog.V(1).Infof("haven't completed %s, stop requested", s.lifecycleSignals.MuxAndDiscoveryComplete.Name())
				return
			}
		}
		s.lifecycleSignals.MuxAndDiscoveryComplete.Signal()
		klog.V(1).Infof("%s has all endpoints registered and discovery information is complete", s.lifecycleSignals.MuxAndDiscoveryComplete.Name())
	}()

	go func() {
		defer delayedStopCh.Signal()
		defer klog.V(1).InfoS("[graceful-termination] shutdown event", "name", delayedStopCh.Name())

		<-stopCh

		// As soon as shutdown is initiated, /readyz should start returning failure.
		// This gives the load balancer a window defined by ShutdownDelayDuration to detect that /readyz is red
		// and stop sending traffic to this server.
		shutdownInitiatedCh.Signal()
		klog.V(1).InfoS("[graceful-termination] shutdown event", "name", shutdownInitiatedCh.Name())

		time.Sleep(s.ShutdownDelayDuration)
	}()

	// close socket after delayed stopCh
	shutdownTimeout := s.ShutdownTimeout
	if s.ShutdownSendRetryAfter {
		// when this mode is enabled, we do the following:
		// - the server will continue to listen until all existing requests in flight
		//   (not including active long running requests) have been drained.
		// - once drained, http Server Shutdown is invoked with a timeout of 2s,
		//   net/http waits for 1s for the peer to respond to a GO_AWAY frame, so
		//   we should wait for a minimum of 2s
		shutdownTimeout = 2 * time.Second
		klog.V(1).InfoS("[graceful-termination] using HTTP Server shutdown timeout", "shutdownTimeout", shutdownTimeout)
	}

	notAcceptingNewRequestCh := s.lifecycleSignals.NotAcceptingNewRequest
	drainedCh := s.lifecycleSignals.InFlightRequestsDrained
	stopHttpServerCh := make(chan struct{})
	go func() {
		defer close(stopHttpServerCh)

		timeToStopHttpServerCh := notAcceptingNewRequestCh.Signaled()
		if s.ShutdownSendRetryAfter {
			timeToStopHttpServerCh = drainedCh.Signaled()
		}

		<-timeToStopHttpServerCh
	}()

	// Start the audit backend before any request comes in. This means we must call Backend.Run
	// before http server start serving. Otherwise the Backend.ProcessEvents call might block.
	// AuditBackend.Run will stop as soon as all in-flight requests are drained.
	if s.AuditBackend != nil {
		if err := s.AuditBackend.Run(drainedCh.Signaled()); err != nil {
			return fmt.Errorf("failed to run the audit backend: %v", err)
		}
	}

	stoppedCh, listenerStoppedCh, err := s.NonBlockingRun(stopHttpServerCh, shutdownTimeout)
	if err != nil {
		return err
	}

	httpServerStoppedListeningCh := s.lifecycleSignals.HTTPServerStoppedListening
	go func() {
		<-listenerStoppedCh
		httpServerStoppedListeningCh.Signal()
		klog.V(1).InfoS("[graceful-termination] shutdown event", "name", httpServerStoppedListeningCh.Name())
	}()

	// we don't accept new request as soon as both ShutdownDelayDuration has
	// elapsed and preshutdown hooks have completed.
	preShutdownHooksHasStoppedCh := s.lifecycleSignals.PreShutdownHooksStopped
	go func() {
		defer klog.V(1).InfoS("[graceful-termination] shutdown event", "name", notAcceptingNewRequestCh.Name())
		defer notAcceptingNewRequestCh.Signal()

		// wait for the delayed stopCh before closing the handler chain
		<-delayedStopCh.Signaled()

		// Additionally wait for preshutdown hooks to also be finished, as some of them need
		// to send API calls to clean up after themselves (e.g. lease reconcilers removing
		// itself from the active servers).
		<-preShutdownHooksHasStoppedCh.Signaled()
	}()

	// wait for all in-flight non-long running requests to finish
	nonLongRunningRequestDrainedCh := make(chan struct{})
	go func() {
		defer close(nonLongRunningRequestDrainedCh)
		defer klog.V(1).Info("[graceful-termination] in-flight non long-running request(s) have drained")

		// wait for the delayed stopCh before closing the handler chain (it rejects everything after Wait has been called).
		<-notAcceptingNewRequestCh.Signaled()

		// Wait for all requests to finish, which are bounded by the RequestTimeout variable.
		// once NonLongRunningRequestWaitGroup.Wait is invoked, the apiserver is
		// expected to reject any incoming request with a {503, Retry-After}
		// response via the WithWaitGroup filter. On the contrary, we observe
		// that incoming request(s) get a 'connection refused' error, this is
		// because, at this point, we have called 'Server.Shutdown' and
		// net/http server has stopped listening. This causes incoming
		// request to get a 'connection refused' error.
		// On the other hand, if 'ShutdownSendRetryAfter' is enabled incoming
		// requests will be rejected with a {429, Retry-After} since
		// 'Server.Shutdown' will be invoked only after in-flight requests
		// have been drained.
		// TODO: can we consolidate these two modes of graceful termination?
		s.NonLongRunningRequestWaitGroup.Wait()
	}()

	// wait for all in-flight watches to finish
	activeWatchesDrainedCh := make(chan struct{})
	go func() {
		defer close(activeWatchesDrainedCh)

		<-notAcceptingNewRequestCh.Signaled()
		if s.ShutdownWatchTerminationGracePeriod <= time.Duration(0) {
			klog.V(1).InfoS("[graceful-termination] not going to wait for active watch request(s) to drain")
			return
		}

		// Wait for all active watches to finish
		grace := s.ShutdownWatchTerminationGracePeriod
		activeBefore, activeAfter, err := s.WatchRequestWaitGroup.Wait(func(count int) (utilwaitgroup.RateLimiter, context.Context, context.CancelFunc) {
			qps := float64(count) / grace.Seconds()
			// TODO: we don't want the QPS (max requests drained per second) to
			//  get below a certain floor value, since we want the server to
			//  drain the active watch requests as soon as possible.
			//  For now, it's hard coded to 200, and it is subject to change
			//  based on the result from the scale testing.
			if qps < 200 {
				qps = 200
			}

			ctx, cancel := context.WithTimeout(context.Background(), grace)
			// We don't expect more than one token to be consumed
			// in a single Wait call, so setting burst to 1.
			return rate.NewLimiter(rate.Limit(qps), 1), ctx, cancel
		})
		klog.V(1).InfoS("[graceful-termination] active watch request(s) have drained",
			"duration", grace, "activeWatchesBefore", activeBefore, "activeWatchesAfter", activeAfter, "error", err)
	}()

	go func() {
		defer klog.V(1).InfoS("[graceful-termination] shutdown event", "name", drainedCh.Name())
		defer drainedCh.Signal()

		<-nonLongRunningRequestDrainedCh
		<-activeWatchesDrainedCh
	}()

	klog.V(1).Info("[graceful-termination] waiting for shutdown to be initiated")
	<-stopCh

	// run shutdown hooks directly. This includes deregistering from
	// the kubernetes endpoint in case of kube-apiserver.
	func() {
		defer func() {
			preShutdownHooksHasStoppedCh.Signal()
			klog.V(1).InfoS("[graceful-termination] pre-shutdown hooks completed", "name", preShutdownHooksHasStoppedCh.Name())
		}()
		err = s.RunPreShutdownHooks()
	}()
	if err != nil {
		return err
	}

	// Wait for all requests in flight to drain, bounded by the RequestTimeout variable.
	<-drainedCh.Signaled()

	if s.AuditBackend != nil {
		s.AuditBackend.Shutdown()
		klog.V(1).InfoS("[graceful-termination] audit backend shutdown completed")
	}

	// wait for stoppedCh that is closed when the graceful termination (server.Shutdown) is finished.
	<-listenerStoppedCh
	<-stoppedCh

	klog.V(1).Info("[graceful-termination] apiserver is exiting")
	return nil
}

// NonBlockingRun spawns the secure http server. An error is
// returned if the secure port cannot be listened on.
// The returned channel is closed when the (asynchronous) termination is finished.
func (s preparedGenericAPIServer) NonBlockingRun(stopCh <-chan struct{}, shutdownTimeout time.Duration) (<-chan struct{}, <-chan struct{}, error) {
	// Use an internal stop channel to allow cleanup of the listeners on error.
	internalStopCh := make(chan struct{})
	var stoppedCh <-chan struct{}
	var listenerStoppedCh <-chan struct{}
	if s.SecureServingInfo != nil && s.Handler != nil {
		var err error
		stoppedCh, listenerStoppedCh, err = s.SecureServingInfo.Serve(s.Handler, shutdownTimeout, internalStopCh)
		if err != nil {
			close(internalStopCh)
			return nil, nil, err
		}
	}

	// Now that listener have bound successfully, it is the
	// responsibility of the caller to close the provided channel to
	// ensure cleanup.
	go func() {
		<-stopCh
		close(internalStopCh)
	}()

	s.RunPostStartHooks(stopCh)

	if _, err := systemd.SdNotify(true, "READY=1\n"); err != nil {
		klog.Errorf("Unable to send systemd daemon successful start message: %v\n", err)
	}

	return stoppedCh, listenerStoppedCh, nil
}

// installAPIResources is a private method for installing the REST storage backing each api groupversionresource
func (s *GenericAPIServer) installAPIResources(apiPrefix string, apiGroupInfo *APIGroupInfo, openAPIModels map[string]*spec.Schema) error {
	var typeConverter managedfields.TypeConverter

	if len(openAPIModels) > 0 {
		var err error
		typeConverter, err = managedfields.NewTypeConverter(openAPIModels, false)
		if err != nil {
			return err
		}
	}
	var resourceInfos []*storageversion.ResourceInfo
	for _, groupVersion := range apiGroupInfo.PrioritizedVersions {
		if len(apiGroupInfo.VersionedResourcesStorageMap[groupVersion.Version]) == 0 {
			klog.Warningf("Skipping API %v because it has no resources.", groupVersion)
			continue
		}

		apiGroupVersion, err := s.getAPIGroupVersion(apiGroupInfo, groupVersion, apiPrefix)
		if err != nil {
			return err
		}
		if apiGroupInfo.OptionsExternalVersion != nil {
			apiGroupVersion.OptionsExternalVersion = apiGroupInfo.OptionsExternalVersion
		}
		apiGroupVersion.TypeConverter = typeConverter
		apiGroupVersion.MaxRequestBodyBytes = s.maxRequestBodyBytes

		discoveryAPIResources, r, err := apiGroupVersion.InstallREST(s.Handler.GoRestfulContainer)

		if err != nil {
			return fmt.Errorf("unable to setup API %v: %v", apiGroupInfo, err)
		}
		resourceInfos = append(resourceInfos, r...)

		if utilfeature.DefaultFeatureGate.Enabled(features.AggregatedDiscoveryEndpoint) {
			// Aggregated discovery only aggregates resources under /apis
			if apiPrefix == APIGroupPrefix {
				s.AggregatedDiscoveryGroupManager.AddGroupVersion(
					groupVersion.Group,
					apidiscoveryv2beta1.APIVersionDiscovery{
						Freshness: apidiscoveryv2beta1.DiscoveryFreshnessCurrent,
						Version:   groupVersion.Version,
						Resources: discoveryAPIResources,
					},
				)
			} else {
				// There is only one group version for legacy resources, priority can be defaulted to 0.
				s.AggregatedLegacyDiscoveryGroupManager.AddGroupVersion(
					groupVersion.Group,
					apidiscoveryv2beta1.APIVersionDiscovery{
						Freshness: apidiscoveryv2beta1.DiscoveryFreshnessCurrent,
						Version:   groupVersion.Version,
						Resources: discoveryAPIResources,
					},
				)
			}
		}

	}

	s.RegisterDestroyFunc(apiGroupInfo.destroyStorage)

	if utilfeature.DefaultFeatureGate.Enabled(features.StorageVersionAPI) &&
		utilfeature.DefaultFeatureGate.Enabled(features.APIServerIdentity) {
		// API installation happens before we start listening on the handlers,
		// therefore it is safe to register ResourceInfos here. The handler will block
		// write requests until the storage versions of the targeting resources are updated.
		s.StorageVersionManager.AddResourceInfo(resourceInfos...)
	}

	return nil
}

// InstallLegacyAPIGroup exposes the given legacy 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.
func (s *GenericAPIServer) InstallLegacyAPIGroup(apiPrefix string, apiGroupInfo *APIGroupInfo) error {
	if !s.legacyAPIGroupPrefixes.Has(apiPrefix) {
		return fmt.Errorf("%q is not in the allowed legacy API prefixes: %v", apiPrefix, s.legacyAPIGroupPrefixes.List())
	}

	openAPIModels, err := s.getOpenAPIModels(apiPrefix, apiGroupInfo)
	if err != nil {
		return fmt.Errorf("unable to get openapi models: %v", err)
	}

	if err := s.installAPIResources(apiPrefix, apiGroupInfo, openAPIModels); err != nil {
		return err
	}

	// Install the version handler.
	// Add a handler at /<apiPrefix> to enumerate the supported api versions.
	legacyRootAPIHandler := discovery.NewLegacyRootAPIHandler(s.discoveryAddresses, s.Serializer, apiPrefix)
	if utilfeature.DefaultFeatureGate.Enabled(features.AggregatedDiscoveryEndpoint) {
		wrapped := discoveryendpoint.WrapAggregatedDiscoveryToHandler(legacyRootAPIHandler, s.AggregatedLegacyDiscoveryGroupManager)
		s.Handler.GoRestfulContainer.Add(wrapped.GenerateWebService("/api", metav1.APIVersions{}))
	} else {
		s.Handler.GoRestfulContainer.Add(legacyRootAPIHandler.WebService())
	}

	return nil
}

// InstallAPIGroups exposes given api groups in the API.
// The <apiGroupInfos> passed into this function shouldn't be used elsewhere as the
// underlying storage will be destroyed on this servers shutdown.
func (s *GenericAPIServer) InstallAPIGroups(apiGroupInfos ...*APIGroupInfo) error {
	for _, apiGroupInfo := range apiGroupInfos {
		// Do not register empty group or empty version.  Doing so claims /apis/ for the wrong entity to be returned.
		// Catching these here places the error  much closer to its origin
		if len(apiGroupInfo.PrioritizedVersions[0].Group) == 0 {
			return fmt.Errorf("cannot register handler with an empty group for %#v", *apiGroupInfo)
		}
		if len(apiGroupInfo.PrioritizedVersions[0].Version) == 0 {
			return fmt.Errorf("cannot register handler with an empty version for %#v", *apiGroupInfo)
		}
	}

	openAPIModels, err := s.getOpenAPIModels(APIGroupPrefix, apiGroupInfos...)
	if err != nil {
		return fmt.Errorf("unable to get openapi models: %v", err)
	}

	for _, apiGroupInfo := range apiGroupInfos {
		if err := s.installAPIResources(APIGroupPrefix, apiGroupInfo, openAPIModels); err != nil {
			return fmt.Errorf("unable to install api resources: %v", err)
		}

		// setup discovery
		// Install the version handler.
		// Add a handler at /apis/<groupName> to enumerate all versions supported by this group.
		apiVersionsForDiscovery := []metav1.GroupVersionForDiscovery{}
		for _, groupVersion := range apiGroupInfo.PrioritizedVersions {
			// Check the config to make sure that we elide versions that don't have any resources
			if len(apiGroupInfo.VersionedResourcesStorageMap[groupVersion.Version]) == 0 {
				continue
			}
			apiVersionsForDiscovery = append(apiVersionsForDiscovery, metav1.GroupVersionForDiscovery{
				GroupVersion: groupVersion.String(),
				Version:      groupVersion.Version,
			})
		}
		preferredVersionForDiscovery := metav1.GroupVersionForDiscovery{
			GroupVersion: apiGroupInfo.PrioritizedVersions[0].String(),
			Version:      apiGroupInfo.PrioritizedVersions[0].Version,
		}
		apiGroup := metav1.APIGroup{
			Name:             apiGroupInfo.PrioritizedVersions[0].Group,
			Versions:         apiVersionsForDiscovery,
			PreferredVersion: preferredVersionForDiscovery,
		}

		s.DiscoveryGroupManager.AddGroup(apiGroup)
		s.Handler.GoRestfulContainer.Add(discovery.NewAPIGroupHandler(s.Serializer, apiGroup).WebService())
	}
	return nil
}

// 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.
func (s *GenericAPIServer) InstallAPIGroup(apiGroupInfo *APIGroupInfo) error {
	return s.InstallAPIGroups(apiGroupInfo)
}

func (s *GenericAPIServer) getAPIGroupVersion(apiGroupInfo *APIGroupInfo, groupVersion schema.GroupVersion, apiPrefix string) (*genericapi.APIGroupVersion, error) {
	storage := make(map[string]rest.Storage)
	for k, v := range apiGroupInfo.VersionedResourcesStorageMap[groupVersion.Version] {
		if strings.ToLower(k) != k {
			return nil, fmt.Errorf("resource names must be lowercase only, not %q", k)
		}
		storage[k] = v
	}
	version := s.newAPIGroupVersion(apiGroupInfo, groupVersion)
	version.Root = apiPrefix
	version.Storage = storage
	return version, nil
}

func (s *GenericAPIServer) newAPIGroupVersion(apiGroupInfo *APIGroupInfo, groupVersion schema.GroupVersion) *genericapi.APIGroupVersion {
	return &genericapi.APIGroupVersion{
		GroupVersion:     groupVersion,
		MetaGroupVersion: apiGroupInfo.MetaGroupVersion,

		ParameterCodec:        apiGroupInfo.ParameterCodec,
		Serializer:            apiGroupInfo.NegotiatedSerializer,
		Creater:               apiGroupInfo.Scheme,
		Convertor:             apiGroupInfo.Scheme,
		ConvertabilityChecker: apiGroupInfo.Scheme,
		UnsafeConvertor:       runtime.UnsafeObjectConvertor(apiGroupInfo.Scheme),
		Defaulter:             apiGroupInfo.Scheme,
		Typer:                 apiGroupInfo.Scheme,
		Namer:                 runtime.Namer(meta.NewAccessor()),

		EquivalentResourceRegistry: s.EquivalentResourceRegistry,

		Admit:             s.admissionControl,
		MinRequestTimeout: s.minRequestTimeout,
		Authorizer:        s.Authorizer,
	}
}

// NewDefaultAPIGroupInfo returns an APIGroupInfo stubbed with "normal" values
// exposed for easier composition from other packages
func NewDefaultAPIGroupInfo(group string, scheme *runtime.Scheme, parameterCodec runtime.ParameterCodec, codecs serializer.CodecFactory) APIGroupInfo {
	return APIGroupInfo{
		PrioritizedVersions:          scheme.PrioritizedVersionsForGroup(group),
		VersionedResourcesStorageMap: map[string]map[string]rest.Storage{},
		// TODO unhardcode this.  It was hardcoded before, but we need to re-evaluate
		OptionsExternalVersion: &schema.GroupVersion{Version: "v1"},
		Scheme:                 scheme,
		ParameterCodec:         parameterCodec,
		NegotiatedSerializer:   codecs,
	}
}

// getOpenAPIModels is a private method for getting the OpenAPI models
func (s *GenericAPIServer) getOpenAPIModels(apiPrefix string, apiGroupInfos ...*APIGroupInfo) (map[string]*spec.Schema, error) {
	if s.openAPIV3Config == nil {
		//!TODO: A future work should add a requirement that
		// OpenAPIV3 config is required. May require some refactoring of tests.
		return nil, nil
	}
	pathsToIgnore := openapiutil.NewTrie(s.openAPIConfig.IgnorePrefixes)
	resourceNames := make([]string, 0)
	for _, apiGroupInfo := range apiGroupInfos {
		groupResources, err := getResourceNamesForGroup(apiPrefix, apiGroupInfo, pathsToIgnore)
		if err != nil {
			return nil, err
		}
		resourceNames = append(resourceNames, groupResources...)
	}

	// Build the openapi definitions for those resources and convert it to proto models
	openAPISpec, err := openapibuilder3.BuildOpenAPIDefinitionsForResources(s.openAPIV3Config, resourceNames...)
	if err != nil {
		return nil, err
	}
	for _, apiGroupInfo := range apiGroupInfos {
		apiGroupInfo.StaticOpenAPISpec = openAPISpec
	}
	return openAPISpec, nil
}

// getResourceNamesForGroup is a private method for getting the canonical names for each resource to build in an api group
func getResourceNamesForGroup(apiPrefix string, apiGroupInfo *APIGroupInfo, pathsToIgnore openapiutil.Trie) ([]string, error) {
	// Get the canonical names of every resource we need to build in this api group
	resourceNames := make([]string, 0)
	for _, groupVersion := range apiGroupInfo.PrioritizedVersions {
		for resource, storage := range apiGroupInfo.VersionedResourcesStorageMap[groupVersion.Version] {
			path := gpath.Join(apiPrefix, groupVersion.Group, groupVersion.Version, resource)
			if !pathsToIgnore.HasPrefix(path) {
				kind, err := genericapi.GetResourceKind(groupVersion, storage, apiGroupInfo.Scheme)
				if err != nil {
					return nil, err
				}
				sampleObject, err := apiGroupInfo.Scheme.New(kind)
				if err != nil {
					return nil, err
				}
				name := openapiutil.GetCanonicalTypeName(sampleObject)
				resourceNames = append(resourceNames, name)
			}
		}
	}

	return resourceNames, nil
}