/*
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 app does all of the work necessary to create a Kubernetes
// APIServer by binding together the API, master and APIServer infrastructure.
// It can be configured and called directly or via the hyperkube framework.
package app

import (
	"crypto/tls"
	"fmt"
	"net"
	"net/http"
	"net/url"
	"os"
	"strconv"
	"strings"
	"time"

	"k8s.io/kubernetes/pkg/kubelet/types"

	"github.com/spf13/cobra"
	"github.com/spf13/pflag"

	extensionsapiserver "k8s.io/apiextensions-apiserver/pkg/apiserver"
	utilerrors "k8s.io/apimachinery/pkg/util/errors"
	utilnet "k8s.io/apimachinery/pkg/util/net"
	"k8s.io/apimachinery/pkg/util/sets"
	utilwait "k8s.io/apimachinery/pkg/util/wait"
	"k8s.io/apiserver/pkg/admission"
	"k8s.io/apiserver/pkg/authentication/authenticator"
	"k8s.io/apiserver/pkg/authorization/authorizer"
	openapinamer "k8s.io/apiserver/pkg/endpoints/openapi"
	genericfeatures "k8s.io/apiserver/pkg/features"
	genericapiserver "k8s.io/apiserver/pkg/server"
	"k8s.io/apiserver/pkg/server/egressselector"
	"k8s.io/apiserver/pkg/server/filters"
	serveroptions "k8s.io/apiserver/pkg/server/options"
	serverstorage "k8s.io/apiserver/pkg/server/storage"
	"k8s.io/apiserver/pkg/storage/etcd3/preflight"
	"k8s.io/apiserver/pkg/util/feature"
	utilfeature "k8s.io/apiserver/pkg/util/feature"
	utilflowcontrol "k8s.io/apiserver/pkg/util/flowcontrol"
	"k8s.io/apiserver/pkg/util/webhook"
	clientgoinformers "k8s.io/client-go/informers"
	clientgoclientset "k8s.io/client-go/kubernetes"
	"k8s.io/client-go/rest"
	"k8s.io/client-go/util/keyutil"
	cloudprovider "k8s.io/cloud-provider"
	cliflag "k8s.io/component-base/cli/flag"
	"k8s.io/component-base/cli/globalflag"
	_ "k8s.io/component-base/metrics/prometheus/workqueue" // for workqueue metric registration
	"k8s.io/component-base/term"
	"k8s.io/component-base/version"
	"k8s.io/component-base/version/verflag"
	"k8s.io/klog/v2"
	aggregatorapiserver "k8s.io/kube-aggregator/pkg/apiserver"
	aggregatorscheme "k8s.io/kube-aggregator/pkg/apiserver/scheme"

	"k8s.io/kubernetes/cmd/kube-apiserver/app/options"
	"k8s.io/kubernetes/pkg/api/legacyscheme"
	"k8s.io/kubernetes/pkg/capabilities"
	"k8s.io/kubernetes/pkg/controlplane"
	"k8s.io/kubernetes/pkg/controlplane/reconcilers"
	"k8s.io/kubernetes/pkg/controlplane/tunneler"
	generatedopenapi "k8s.io/kubernetes/pkg/generated/openapi"
	"k8s.io/kubernetes/pkg/kubeapiserver"
	kubeapiserveradmission "k8s.io/kubernetes/pkg/kubeapiserver/admission"
	kubeauthenticator "k8s.io/kubernetes/pkg/kubeapiserver/authenticator"
	"k8s.io/kubernetes/pkg/kubeapiserver/authorizer/modes"
	rbacrest "k8s.io/kubernetes/pkg/registry/rbac/rest"
	"k8s.io/kubernetes/pkg/serviceaccount"
)

const (
	etcdRetryLimit    = 60
	etcdRetryInterval = 1 * time.Second
)

var (
	DefaultProxyDialerFn utilnet.DialFunc
)

// TODO: delete this check after insecure flags removed in v1.24
func checkNonZeroInsecurePort(fs *pflag.FlagSet) error {
	for _, name := range options.InsecurePortFlags {
		val, err := fs.GetInt(name)
		if err != nil {
			return err
		}
		if val != 0 {
			return fmt.Errorf("invalid port value %d: only zero is allowed", val)
		}
	}
	return nil
}

// NewAPIServerCommand creates a *cobra.Command object with default parameters
func NewAPIServerCommand(stopCh <-chan struct{}) *cobra.Command {
	s := options.NewServerRunOptions()
	cmd := &cobra.Command{
		Use: "kube-apiserver",
		Long: `The Kubernetes API server validates and configures data
for the api objects which include pods, services, replicationcontrollers, and
others. The API Server services REST operations and provides the frontend to the
cluster's shared state through which all other components interact.`,

		// stop printing usage when the command errors
		SilenceUsage: true,
		PersistentPreRunE: func(*cobra.Command, []string) error {
			// silence client-go warnings.
			// kube-apiserver loopback clients should not log self-issued warnings.
			rest.SetDefaultWarningHandler(rest.NoWarnings{})
			return nil
		},
		RunE: func(cmd *cobra.Command, args []string) error {
			verflag.PrintAndExitIfRequested()
			fs := cmd.Flags()
			cliflag.PrintFlags(fs)

			err := checkNonZeroInsecurePort(fs)
			if err != nil {
				return err
			}
			// set default options
			completedOptions, err := Complete(s)
			if err != nil {
				return err
			}

			// validate options
			if errs := completedOptions.Validate(); len(errs) != 0 {
				return utilerrors.NewAggregate(errs)
			}

			return Run(completedOptions, stopCh)
		},
		Args: func(cmd *cobra.Command, args []string) error {
			for _, arg := range args {
				if len(arg) > 0 {
					return fmt.Errorf("%q does not take any arguments, got %q", cmd.CommandPath(), args)
				}
			}
			return nil
		},
	}

	fs := cmd.Flags()
	namedFlagSets := s.Flags()
	verflag.AddFlags(namedFlagSets.FlagSet("global"))
	globalflag.AddGlobalFlags(namedFlagSets.FlagSet("global"), cmd.Name())
	options.AddCustomGlobalFlags(namedFlagSets.FlagSet("generic"))
	for _, f := range namedFlagSets.FlagSets {
		fs.AddFlagSet(f)
	}

	usageFmt := "Usage:\n  %s\n"
	cols, _, _ := term.TerminalSize(cmd.OutOrStdout())
	cmd.SetUsageFunc(func(cmd *cobra.Command) error {
		fmt.Fprintf(cmd.OutOrStderr(), usageFmt, cmd.UseLine())
		cliflag.PrintSections(cmd.OutOrStderr(), namedFlagSets, cols)
		return nil
	})
	cmd.SetHelpFunc(func(cmd *cobra.Command, args []string) {
		fmt.Fprintf(cmd.OutOrStdout(), "%s\n\n"+usageFmt, cmd.Long, cmd.UseLine())
		cliflag.PrintSections(cmd.OutOrStdout(), namedFlagSets, cols)
	})

	return cmd
}

type startupConfig struct {
	Handler       http.Handler
	Authenticator authenticator.Request
}

var StartupConfig = make(chan startupConfig, 1)

// Run runs the specified APIServer.  This should never exit.
func Run(completeOptions completedServerRunOptions, stopCh <-chan struct{}) error {
	// To help debugging, immediately log version
	klog.Infof("Version: %+v", version.Get())

	server, err := CreateServerChain(completeOptions, stopCh)
	if err != nil {
		return err
	}

	prepared, err := server.PrepareRun()
	if err != nil {
		return err
	}

	return prepared.Run(stopCh)
}

// CreateServerChain creates the apiservers connected via delegation.
func CreateServerChain(completedOptions completedServerRunOptions, stopCh <-chan struct{}) (*aggregatorapiserver.APIAggregator, error) {
	nodeTunneler, proxyTransport, err := CreateNodeDialer(completedOptions)
	if err != nil {
		return nil, err
	}

	if DefaultProxyDialerFn != nil {
		completedOptions.KubeletConfig.Dial = DefaultProxyDialerFn
		completedOptions.KubeletConfig.Proxy = http.ProxyURL(nil)
	}

	kubeAPIServerConfig, serviceResolver, pluginInitializer, err := CreateKubeAPIServerConfig(completedOptions, nodeTunneler, proxyTransport)
	if err != nil {
		return nil, err
	}

	// If additional API servers are added, they should be gated.
	apiExtensionsConfig, err := createAPIExtensionsConfig(*kubeAPIServerConfig.GenericConfig, kubeAPIServerConfig.ExtraConfig.VersionedInformers, pluginInitializer, completedOptions.ServerRunOptions, completedOptions.MasterCount,
		serviceResolver, webhook.NewDefaultAuthenticationInfoResolverWrapper(proxyTransport, kubeAPIServerConfig.GenericConfig.EgressSelector, kubeAPIServerConfig.GenericConfig.LoopbackClientConfig))
	if err != nil {
		return nil, err
	}
	apiExtensionsServer, err := createAPIExtensionsServer(apiExtensionsConfig, genericapiserver.NewEmptyDelegate())
	if err != nil {
		return nil, err
	}

	kubeAPIServer, err := CreateKubeAPIServer(kubeAPIServerConfig, apiExtensionsServer.GenericAPIServer)
	if err != nil {
		return nil, err
	}

	// aggregator comes last in the chain
	aggregatorConfig, err := createAggregatorConfig(*kubeAPIServerConfig.GenericConfig, completedOptions.ServerRunOptions, kubeAPIServerConfig.ExtraConfig.VersionedInformers, serviceResolver, proxyTransport, pluginInitializer)
	if err != nil {
		return nil, err
	}
	aggregatorServer, err := createAggregatorServer(aggregatorConfig, kubeAPIServer.GenericAPIServer, apiExtensionsServer.Informers)
	if err != nil {
		// we don't need special handling for innerStopCh because the aggregator server doesn't create any go routines
		return nil, err
	}

	StartupConfig <- startupConfig{
		Handler:       aggregatorServer.GenericAPIServer.Handler,
		Authenticator: kubeAPIServerConfig.GenericConfig.Authentication.Authenticator,
	}
	close(StartupConfig)

	return aggregatorServer, nil
}

// CreateKubeAPIServer creates and wires a workable kube-apiserver
func CreateKubeAPIServer(kubeAPIServerConfig *controlplane.Config, delegateAPIServer genericapiserver.DelegationTarget) (*controlplane.Instance, error) {
	kubeAPIServer, err := kubeAPIServerConfig.Complete().New(delegateAPIServer)
	if err != nil {
		return nil, err
	}

	return kubeAPIServer, nil
}

// CreateNodeDialer creates the dialer infrastructure to connect to the nodes.
func CreateNodeDialer(s completedServerRunOptions) (tunneler.Tunneler, *http.Transport, error) {
	// Setup nodeTunneler if needed
	var nodeTunneler tunneler.Tunneler
	var proxyDialerFn utilnet.DialFunc
	if len(s.SSHUser) > 0 {
		// Get ssh key distribution func, if supported
		var installSSHKey tunneler.InstallSSHKey

		cloudprovider.DeprecationWarningForProvider(s.CloudProvider.CloudProvider)
		cloud, err := cloudprovider.InitCloudProvider(s.CloudProvider.CloudProvider, s.CloudProvider.CloudConfigFile)
		if err != nil {
			return nil, nil, fmt.Errorf("cloud provider could not be initialized: %v", err)
		}
		if cloud != nil {
			if instances, supported := cloud.Instances(); supported {
				installSSHKey = instances.AddSSHKeyToAllInstances
			}
		}
		if s.KubeletConfig.Port == 0 {
			return nil, nil, fmt.Errorf("must enable kubelet port if proxy ssh-tunneling is specified")
		}
		if s.KubeletConfig.ReadOnlyPort == 0 {
			return nil, nil, fmt.Errorf("must enable kubelet readonly port if proxy ssh-tunneling is specified")
		}
		// Set up the nodeTunneler
		// TODO(cjcullen): If we want this to handle per-kubelet ports or other
		// kubelet listen-addresses, we need to plumb through options.
		healthCheckPath := &url.URL{
			Scheme: "http",
			Host:   net.JoinHostPort("127.0.0.1", strconv.FormatUint(uint64(s.KubeletConfig.ReadOnlyPort), 10)),
			Path:   "healthz",
		}
		nodeTunneler = tunneler.New(s.SSHUser, s.SSHKeyfile, healthCheckPath, installSSHKey)

		// Use the nodeTunneler's dialer when proxying to pods, services, and nodes
		proxyDialerFn = nodeTunneler.Dial
	}
	// Proxying to pods and services is IP-based... don't expect to be able to verify the hostname
	proxyTLSClientConfig := &tls.Config{InsecureSkipVerify: true}
	proxyTransport := utilnet.SetTransportDefaults(&http.Transport{
		DialContext:     proxyDialerFn,
		TLSClientConfig: proxyTLSClientConfig,
	})
	return nodeTunneler, proxyTransport, nil
}

// CreateKubeAPIServerConfig creates all the resources for running the API server, but runs none of them
func CreateKubeAPIServerConfig(
	s completedServerRunOptions,
	nodeTunneler tunneler.Tunneler,
	proxyTransport *http.Transport,
) (
	*controlplane.Config,
	aggregatorapiserver.ServiceResolver,
	[]admission.PluginInitializer,
	error,
) {
	genericConfig, versionedInformers, serviceResolver, pluginInitializers, admissionPostStartHook, storageFactory, err := buildGenericConfig(s.ServerRunOptions, proxyTransport)
	if err != nil {
		return nil, nil, nil, err
	}

	if _, port, err := net.SplitHostPort(s.Etcd.StorageConfig.Transport.ServerList[0]); err == nil && port != "0" && len(port) != 0 {
		if err := utilwait.PollImmediate(etcdRetryInterval, etcdRetryLimit*etcdRetryInterval, preflight.EtcdConnection{ServerList: s.Etcd.StorageConfig.Transport.ServerList}.CheckEtcdServers); err != nil {
			return nil, nil, nil, fmt.Errorf("error waiting for etcd connection: %v", err)
		}
	}

	all, _ := types.GetValidatedSources([]string{types.AllSource})

	capabilities.Initialize(capabilities.Capabilities{
		AllowPrivileged: s.AllowPrivileged,
		// TODO(vmarmol): Implement support for HostNetworkSources.
		PrivilegedSources: capabilities.PrivilegedSources{
			HostNetworkSources: all,
			HostPIDSources:     all,
			HostIPCSources:     all,
		},
		PerConnectionBandwidthLimitBytesPerSec: s.MaxConnectionBytesPerSec,
	})

	s.Metrics.Apply()
	serviceaccount.RegisterMetrics()

	s.Logs.Apply()

	serviceIPRange, apiServerServiceIP, err := controlplane.ServiceIPRange(s.PrimaryServiceClusterIPRange)
	if err != nil {
		return nil, nil, nil, err
	}

	// defaults to empty range and ip
	var secondaryServiceIPRange net.IPNet
	// process secondary range only if provided by user
	if s.SecondaryServiceClusterIPRange.IP != nil {
		secondaryServiceIPRange, _, err = controlplane.ServiceIPRange(s.SecondaryServiceClusterIPRange)
		if err != nil {
			return nil, nil, nil, err
		}
	}

	config := &controlplane.Config{
		GenericConfig: genericConfig,
		ExtraConfig: controlplane.ExtraConfig{
			APIResourceConfigSource: storageFactory.APIResourceConfigSource,
			StorageFactory:          storageFactory,
			EventTTL:                s.EventTTL,
			KubeletClientConfig:     s.KubeletConfig,
			EnableLogsSupport:       s.EnableLogsHandler,
			ProxyTransport:          proxyTransport,

			Tunneler: nodeTunneler,

			ServiceIPRange:          serviceIPRange,
			APIServerServiceIP:      apiServerServiceIP,
			SecondaryServiceIPRange: secondaryServiceIPRange,

			APIServerServicePort: 443,

			ServiceNodePortRange:      s.ServiceNodePortRange,
			KubernetesServiceNodePort: s.KubernetesServiceNodePort,

			EndpointReconcilerType: reconcilers.Type(s.EndpointReconcilerType),
			MasterCount:            s.MasterCount,

			ServiceAccountIssuer:        s.ServiceAccountIssuer,
			ServiceAccountMaxExpiration: s.ServiceAccountTokenMaxExpiration,
			ExtendExpiration:            s.Authentication.ServiceAccounts.ExtendExpiration,

			VersionedInformers: versionedInformers,

			IdentityLeaseDurationSeconds:      s.IdentityLeaseDurationSeconds,
			IdentityLeaseRenewIntervalSeconds: s.IdentityLeaseRenewIntervalSeconds,
		},
	}

	clientCAProvider, err := s.Authentication.ClientCert.GetClientCAContentProvider()
	if err != nil {
		return nil, nil, nil, err
	}
	config.ExtraConfig.ClusterAuthenticationInfo.ClientCA = clientCAProvider

	requestHeaderConfig, err := s.Authentication.RequestHeader.ToAuthenticationRequestHeaderConfig()
	if err != nil {
		return nil, nil, nil, err
	}
	if requestHeaderConfig != nil {
		config.ExtraConfig.ClusterAuthenticationInfo.RequestHeaderCA = requestHeaderConfig.CAContentProvider
		config.ExtraConfig.ClusterAuthenticationInfo.RequestHeaderAllowedNames = requestHeaderConfig.AllowedClientNames
		config.ExtraConfig.ClusterAuthenticationInfo.RequestHeaderExtraHeaderPrefixes = requestHeaderConfig.ExtraHeaderPrefixes
		config.ExtraConfig.ClusterAuthenticationInfo.RequestHeaderGroupHeaders = requestHeaderConfig.GroupHeaders
		config.ExtraConfig.ClusterAuthenticationInfo.RequestHeaderUsernameHeaders = requestHeaderConfig.UsernameHeaders
	}

	if err := config.GenericConfig.AddPostStartHook("start-kube-apiserver-admission-initializer", admissionPostStartHook); err != nil {
		return nil, nil, nil, err
	}

	if nodeTunneler != nil {
		// Use the nodeTunneler's dialer to connect to the kubelet
		config.ExtraConfig.KubeletClientConfig.Dial = nodeTunneler.Dial
	}
	if config.GenericConfig.EgressSelector != nil {
		// Use the config.GenericConfig.EgressSelector lookup to find the dialer to connect to the kubelet
		config.ExtraConfig.KubeletClientConfig.Lookup = config.GenericConfig.EgressSelector.Lookup

		// Use the config.GenericConfig.EgressSelector lookup as the transport used by the "proxy" subresources.
		networkContext := egressselector.Cluster.AsNetworkContext()
		dialer, err := config.GenericConfig.EgressSelector.Lookup(networkContext)
		if err != nil {
			return nil, nil, nil, err
		}
		c := proxyTransport.Clone()
		c.DialContext = dialer
		config.ExtraConfig.ProxyTransport = c
	}

	// Load the public keys.
	var pubKeys []interface{}
	for _, f := range s.Authentication.ServiceAccounts.KeyFiles {
		keys, err := keyutil.PublicKeysFromFile(f)
		if err != nil {
			return nil, nil, nil, fmt.Errorf("failed to parse key file %q: %v", f, err)
		}
		pubKeys = append(pubKeys, keys...)
	}
	// Plumb the required metadata through ExtraConfig.
	config.ExtraConfig.ServiceAccountIssuerURL = s.Authentication.ServiceAccounts.Issuer
	config.ExtraConfig.ServiceAccountJWKSURI = s.Authentication.ServiceAccounts.JWKSURI
	config.ExtraConfig.ServiceAccountPublicKeys = pubKeys

	return config, serviceResolver, pluginInitializers, nil
}

// BuildGenericConfig takes the master server options and produces the genericapiserver.Config associated with it
func buildGenericConfig(
	s *options.ServerRunOptions,
	proxyTransport *http.Transport,
) (
	genericConfig *genericapiserver.Config,
	versionedInformers clientgoinformers.SharedInformerFactory,
	serviceResolver aggregatorapiserver.ServiceResolver,
	pluginInitializers []admission.PluginInitializer,
	admissionPostStartHook genericapiserver.PostStartHookFunc,
	storageFactory *serverstorage.DefaultStorageFactory,
	lastErr error,
) {
	genericConfig = genericapiserver.NewConfig(legacyscheme.Codecs)
	genericConfig.MergedResourceConfig = controlplane.DefaultAPIResourceConfigSource()

	if lastErr = s.GenericServerRunOptions.ApplyTo(genericConfig); lastErr != nil {
		return
	}

	if lastErr = s.SecureServing.ApplyTo(&genericConfig.SecureServing, &genericConfig.LoopbackClientConfig); lastErr != nil {
		return
	}
	if lastErr = s.Features.ApplyTo(genericConfig); lastErr != nil {
		return
	}
	if lastErr = s.APIEnablement.ApplyTo(genericConfig, controlplane.DefaultAPIResourceConfigSource(), legacyscheme.Scheme); lastErr != nil {
		return
	}
	if lastErr = s.EgressSelector.ApplyTo(genericConfig); lastErr != nil {
		return
	}

	genericConfig.OpenAPIConfig = genericapiserver.DefaultOpenAPIConfig(generatedopenapi.GetOpenAPIDefinitions, openapinamer.NewDefinitionNamer(legacyscheme.Scheme, extensionsapiserver.Scheme, aggregatorscheme.Scheme))
	genericConfig.OpenAPIConfig.Info.Title = "Kubernetes"
	genericConfig.LongRunningFunc = filters.BasicLongRunningRequestCheck(
		sets.NewString("watch", "proxy"),
		sets.NewString("attach", "exec", "proxy", "log", "portforward"),
	)

	kubeVersion := version.Get()
	genericConfig.Version = &kubeVersion

	storageFactoryConfig := kubeapiserver.NewStorageFactoryConfig()
	storageFactoryConfig.APIResourceConfig = genericConfig.MergedResourceConfig
	completedStorageFactoryConfig, err := storageFactoryConfig.Complete(s.Etcd)
	if err != nil {
		lastErr = err
		return
	}
	storageFactory, lastErr = completedStorageFactoryConfig.New()
	if lastErr != nil {
		return
	}
	if genericConfig.EgressSelector != nil {
		storageFactory.StorageConfig.Transport.EgressLookup = genericConfig.EgressSelector.Lookup
	}
	if lastErr = s.Etcd.ApplyWithStorageFactoryTo(storageFactory, genericConfig); lastErr != nil {
		return
	}

	// Use protobufs for self-communication.
	// Since not every generic apiserver has to support protobufs, we
	// cannot default to it in generic apiserver and need to explicitly
	// set it in kube-apiserver.
	genericConfig.LoopbackClientConfig.ContentConfig.ContentType = "application/vnd.kubernetes.protobuf"
	// Disable compression for self-communication, since we are going to be
	// on a fast local network
	genericConfig.LoopbackClientConfig.DisableCompression = true

	kubeClientConfig := genericConfig.LoopbackClientConfig
	clientgoExternalClient, err := clientgoclientset.NewForConfig(kubeClientConfig)
	if err != nil {
		lastErr = fmt.Errorf("failed to create real external clientset: %v", err)
		return
	}
	versionedInformers = clientgoinformers.NewSharedInformerFactory(clientgoExternalClient, 10*time.Minute)

	// Authentication.ApplyTo requires already applied OpenAPIConfig and EgressSelector if present
	if lastErr = s.Authentication.ApplyTo(&genericConfig.Authentication, genericConfig.SecureServing, genericConfig.EgressSelector, genericConfig.OpenAPIConfig, clientgoExternalClient, versionedInformers); lastErr != nil {
		return
	}

	genericConfig.Authorization.Authorizer, genericConfig.RuleResolver, err = BuildAuthorizer(s, genericConfig.EgressSelector, versionedInformers)
	if err != nil {
		lastErr = fmt.Errorf("invalid authorization config: %v", err)
		return
	}
	if !sets.NewString(s.Authorization.Modes...).Has(modes.ModeRBAC) {
		genericConfig.DisabledPostStartHooks.Insert(rbacrest.PostStartHookName)
	}

	lastErr = s.Audit.ApplyTo(genericConfig)
	if lastErr != nil {
		return
	}

	admissionConfig := &kubeapiserveradmission.Config{
		ExternalInformers:    versionedInformers,
		LoopbackClientConfig: genericConfig.LoopbackClientConfig,
		CloudConfigFile:      s.CloudProvider.CloudConfigFile,
	}
	serviceResolver = buildServiceResolver(s.EnableAggregatorRouting, genericConfig.LoopbackClientConfig.Host, versionedInformers)
	pluginInitializers, admissionPostStartHook, err = admissionConfig.New(proxyTransport, genericConfig.EgressSelector, serviceResolver)
	if err != nil {
		lastErr = fmt.Errorf("failed to create admission plugin initializer: %v", err)
		return
	}

	err = s.Admission.ApplyTo(
		genericConfig,
		versionedInformers,
		kubeClientConfig,
		feature.DefaultFeatureGate,
		pluginInitializers...)
	if err != nil {
		lastErr = fmt.Errorf("failed to initialize admission: %v", err)
	}

	if utilfeature.DefaultFeatureGate.Enabled(genericfeatures.APIPriorityAndFairness) && s.GenericServerRunOptions.EnablePriorityAndFairness {
		genericConfig.FlowControl = BuildPriorityAndFairness(s, clientgoExternalClient, versionedInformers)
	}

	return
}

// BuildAuthorizer constructs the authorizer
func BuildAuthorizer(s *options.ServerRunOptions, EgressSelector *egressselector.EgressSelector, versionedInformers clientgoinformers.SharedInformerFactory) (authorizer.Authorizer, authorizer.RuleResolver, error) {
	authorizationConfig := s.Authorization.ToAuthorizationConfig(versionedInformers)

	if EgressSelector != nil {
		egressDialer, err := EgressSelector.Lookup(egressselector.ControlPlane.AsNetworkContext())
		if err != nil {
			return nil, nil, err
		}
		authorizationConfig.CustomDial = egressDialer
	}

	return authorizationConfig.New()
}

// BuildPriorityAndFairness constructs the guts of the API Priority and Fairness filter
func BuildPriorityAndFairness(s *options.ServerRunOptions, extclient clientgoclientset.Interface, versionedInformer clientgoinformers.SharedInformerFactory) utilflowcontrol.Interface {
	return utilflowcontrol.New(
		versionedInformer,
		extclient.FlowcontrolV1beta1(),
		s.GenericServerRunOptions.MaxRequestsInFlight+s.GenericServerRunOptions.MaxMutatingRequestsInFlight,
		s.GenericServerRunOptions.RequestTimeout/4,
	)
}

// completedServerRunOptions is a private wrapper that enforces a call of Complete() before Run can be invoked.
type completedServerRunOptions struct {
	*options.ServerRunOptions
}

// Complete set default ServerRunOptions.
// Should be called after kube-apiserver flags parsed.
func Complete(s *options.ServerRunOptions) (completedServerRunOptions, error) {
	var options completedServerRunOptions
	// set defaults
	if err := s.GenericServerRunOptions.DefaultAdvertiseAddress(s.SecureServing.SecureServingOptions); err != nil {
		return options, err
	}

	// process s.ServiceClusterIPRange from list to Primary and Secondary
	// we process secondary only if provided by user
	apiServerServiceIP, primaryServiceIPRange, secondaryServiceIPRange, err := getServiceIPAndRanges(s.ServiceClusterIPRanges)
	if err != nil {
		return options, err
	}
	s.PrimaryServiceClusterIPRange = primaryServiceIPRange
	s.SecondaryServiceClusterIPRange = secondaryServiceIPRange

	if err := s.SecureServing.MaybeDefaultWithSelfSignedCerts(s.GenericServerRunOptions.AdvertiseAddress.String(), []string{"kubernetes.default.svc", "kubernetes.default", "kubernetes"}, []net.IP{apiServerServiceIP}); err != nil {
		return options, fmt.Errorf("error creating self-signed certificates: %v", err)
	}

	if len(s.GenericServerRunOptions.ExternalHost) == 0 {
		if len(s.GenericServerRunOptions.AdvertiseAddress) > 0 {
			s.GenericServerRunOptions.ExternalHost = s.GenericServerRunOptions.AdvertiseAddress.String()
		} else {
			if hostname, err := os.Hostname(); err == nil {
				s.GenericServerRunOptions.ExternalHost = hostname
			} else {
				return options, fmt.Errorf("error finding host name: %v", err)
			}
		}
		klog.Infof("external host was not specified, using %v", s.GenericServerRunOptions.ExternalHost)
	}

	s.Authentication.ApplyAuthorization(s.Authorization)

	// Use (ServiceAccountSigningKeyFile != "") as a proxy to the user enabling
	// TokenRequest functionality. This defaulting was convenient, but messed up
	// a lot of people when they rotated their serving cert with no idea it was
	// connected to their service account keys. We are taking this opportunity to
	// remove this problematic defaulting.
	if s.ServiceAccountSigningKeyFile == "" {
		// Default to the private server key for service account token signing
		if len(s.Authentication.ServiceAccounts.KeyFiles) == 0 && s.SecureServing.ServerCert.CertKey.KeyFile != "" {
			if kubeauthenticator.IsValidServiceAccountKeyFile(s.SecureServing.ServerCert.CertKey.KeyFile) {
				s.Authentication.ServiceAccounts.KeyFiles = []string{s.SecureServing.ServerCert.CertKey.KeyFile}
			} else {
				klog.Warning("No TLS key provided, service account token authentication disabled")
			}
		}
	}

	if s.ServiceAccountSigningKeyFile != "" && s.Authentication.ServiceAccounts.Issuer != "" {
		sk, err := keyutil.PrivateKeyFromFile(s.ServiceAccountSigningKeyFile)
		if err != nil {
			return options, fmt.Errorf("failed to parse service-account-issuer-key-file: %v", err)
		}
		if s.Authentication.ServiceAccounts.MaxExpiration != 0 {
			lowBound := time.Hour
			upBound := time.Duration(1<<32) * time.Second
			if s.Authentication.ServiceAccounts.MaxExpiration < lowBound ||
				s.Authentication.ServiceAccounts.MaxExpiration > upBound {
				return options, fmt.Errorf("the service-account-max-token-expiration must be between 1 hour and 2^32 seconds")
			}
			if s.Authentication.ServiceAccounts.ExtendExpiration {
				if s.Authentication.ServiceAccounts.MaxExpiration < serviceaccount.WarnOnlyBoundTokenExpirationSeconds*time.Second {
					klog.Warningf("service-account-extend-token-expiration is true, in order to correctly trigger safe transition logic, service-account-max-token-expiration must be set longer than %d seconds (currently %s)", serviceaccount.WarnOnlyBoundTokenExpirationSeconds, s.Authentication.ServiceAccounts.MaxExpiration)
				}
				if s.Authentication.ServiceAccounts.MaxExpiration < serviceaccount.ExpirationExtensionSeconds*time.Second {
					klog.Warningf("service-account-extend-token-expiration is true, enabling tokens valid up to %d seconds, which is longer than service-account-max-token-expiration set to %s seconds", serviceaccount.ExpirationExtensionSeconds, s.Authentication.ServiceAccounts.MaxExpiration)
				}
			}
		}

		s.ServiceAccountIssuer, err = serviceaccount.JWTTokenGenerator(s.Authentication.ServiceAccounts.Issuer, sk)
		if err != nil {
			return options, fmt.Errorf("failed to build token generator: %v", err)
		}
		s.ServiceAccountTokenMaxExpiration = s.Authentication.ServiceAccounts.MaxExpiration
	}

	if s.Etcd.EnableWatchCache {
		sizes := kubeapiserver.DefaultWatchCacheSizes()
		// Ensure that overrides parse correctly.
		userSpecified, err := serveroptions.ParseWatchCacheSizes(s.Etcd.WatchCacheSizes)
		if err != nil {
			return options, err
		}
		for resource, size := range userSpecified {
			sizes[resource] = size
		}
		s.Etcd.WatchCacheSizes, err = serveroptions.WriteWatchCacheSizes(sizes)
		if err != nil {
			return options, err
		}
	}

	if s.APIEnablement.RuntimeConfig != nil {
		for key, value := range s.APIEnablement.RuntimeConfig {
			if key == "v1" || strings.HasPrefix(key, "v1/") ||
				key == "api/v1" || strings.HasPrefix(key, "api/v1/") {
				delete(s.APIEnablement.RuntimeConfig, key)
				s.APIEnablement.RuntimeConfig["/v1"] = value
			}
			if key == "api/legacy" {
				delete(s.APIEnablement.RuntimeConfig, key)
			}
		}
	}
	options.ServerRunOptions = s
	return options, nil
}

func buildServiceResolver(enabledAggregatorRouting bool, hostname string, informer clientgoinformers.SharedInformerFactory) webhook.ServiceResolver {
	var serviceResolver webhook.ServiceResolver
	if enabledAggregatorRouting {
		serviceResolver = aggregatorapiserver.NewEndpointServiceResolver(
			informer.Core().V1().Services().Lister(),
			informer.Core().V1().Endpoints().Lister(),
		)
	} else {
		serviceResolver = aggregatorapiserver.NewClusterIPServiceResolver(
			informer.Core().V1().Services().Lister(),
		)
	}
	// resolve kubernetes.default.svc locally
	if localHost, err := url.Parse(hostname); err == nil {
		serviceResolver = aggregatorapiserver.NewLoopbackServiceResolver(serviceResolver, localHost)
	}
	return serviceResolver
}

func getServiceIPAndRanges(serviceClusterIPRanges string) (net.IP, net.IPNet, net.IPNet, error) {
	serviceClusterIPRangeList := []string{}
	if serviceClusterIPRanges != "" {
		serviceClusterIPRangeList = strings.Split(serviceClusterIPRanges, ",")
	}

	var apiServerServiceIP net.IP
	var primaryServiceIPRange net.IPNet
	var secondaryServiceIPRange net.IPNet
	var err error
	// nothing provided by user, use default range (only applies to the Primary)
	if len(serviceClusterIPRangeList) == 0 {
		var primaryServiceClusterCIDR net.IPNet
		primaryServiceIPRange, apiServerServiceIP, err = controlplane.ServiceIPRange(primaryServiceClusterCIDR)
		if err != nil {
			return net.IP{}, net.IPNet{}, net.IPNet{}, fmt.Errorf("error determining service IP ranges: %v", err)
		}
		return apiServerServiceIP, primaryServiceIPRange, net.IPNet{}, nil
	}

	if len(serviceClusterIPRangeList) > 0 {
		_, primaryServiceClusterCIDR, err := net.ParseCIDR(serviceClusterIPRangeList[0])
		if err != nil {
			return net.IP{}, net.IPNet{}, net.IPNet{}, fmt.Errorf("service-cluster-ip-range[0] is not a valid cidr")
		}

		primaryServiceIPRange, apiServerServiceIP, err = controlplane.ServiceIPRange(*(primaryServiceClusterCIDR))
		if err != nil {
			return net.IP{}, net.IPNet{}, net.IPNet{}, fmt.Errorf("error determining service IP ranges for primary service cidr: %v", err)
		}
	}

	// user provided at least two entries
	// note: validation asserts that the list is max of two dual stack entries
	if len(serviceClusterIPRangeList) > 1 {
		_, secondaryServiceClusterCIDR, err := net.ParseCIDR(serviceClusterIPRangeList[1])
		if err != nil {
			return net.IP{}, net.IPNet{}, net.IPNet{}, fmt.Errorf("service-cluster-ip-range[1] is not an ip net")
		}
		secondaryServiceIPRange = *secondaryServiceClusterCIDR
	}
	return apiServerServiceIP, primaryServiceIPRange, secondaryServiceIPRange, nil
}