k3s/vendor/k8s.io/kubernetes/cmd/kube-apiserver/app/server.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 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"
	"io/ioutil"
	"net"
	"net/http"
	"net/url"
	"os"
	"strings"
	"time"

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

	"github.com/spf13/cobra"

	utilerrors "k8s.io/apimachinery/pkg/util/errors"
	utilnet "k8s.io/apimachinery/pkg/util/net"
	"k8s.io/apimachinery/pkg/util/sets"
	"k8s.io/apiserver/pkg/admission"
	"k8s.io/apiserver/pkg/authentication/authenticator"
	"k8s.io/apiserver/pkg/authorization/authorizer"
	genericapiserver "k8s.io/apiserver/pkg/server"
	"k8s.io/apiserver/pkg/server/filters"
	serveroptions "k8s.io/apiserver/pkg/server/options"
	serverstorage "k8s.io/apiserver/pkg/server/storage"
	apiserverflag "k8s.io/apiserver/pkg/util/flag"
	"k8s.io/apiserver/pkg/util/globalflag"
	"k8s.io/apiserver/pkg/util/webhook"
	clientgoinformers "k8s.io/client-go/informers"
	clientgoclientset "k8s.io/client-go/kubernetes"
	certutil "k8s.io/client-go/util/cert"
	"k8s.io/klog"
	aggregatorapiserver "k8s.io/kube-aggregator/pkg/apiserver"
	"k8s.io/kubernetes/cmd/kube-apiserver/app/options"
	"k8s.io/kubernetes/pkg/api/legacyscheme"
	"k8s.io/kubernetes/pkg/capabilities"
	serviceaccountcontroller "k8s.io/kubernetes/pkg/controller/serviceaccount"
	"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"
	kubeoptions "k8s.io/kubernetes/pkg/kubeapiserver/options"
	kubeserver "k8s.io/kubernetes/pkg/kubeapiserver/server"
	"k8s.io/kubernetes/pkg/master"
	"k8s.io/kubernetes/pkg/master/reconcilers"
	"k8s.io/kubernetes/pkg/registry/cachesize"
	rbacrest "k8s.io/kubernetes/pkg/registry/rbac/rest"
	"k8s.io/kubernetes/pkg/serviceaccount"

	utilflag "k8s.io/kubernetes/pkg/util/flag"
	_ "k8s.io/kubernetes/pkg/util/reflector/prometheus" // for reflector metric registration
	_ "k8s.io/kubernetes/pkg/util/workqueue/prometheus" // for workqueue metric registration
	"k8s.io/kubernetes/pkg/version"
	"k8s.io/kubernetes/pkg/version/verflag"
)

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

var (
	DefaultProxyDialerFn utilnet.DialFunc
)

// 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.`,
		RunE: func(cmd *cobra.Command, args []string) error {
			verflag.PrintAndExitIfRequested()
			utilflag.PrintFlags(cmd.Flags())

			// 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)
		},
	}

	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, _, _ := apiserverflag.TerminalSize(cmd.OutOrStdout())
	cmd.SetUsageFunc(func(cmd *cobra.Command) error {
		fmt.Fprintf(cmd.OutOrStderr(), usageFmt, cmd.UseLine())
		apiserverflag.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())
		apiserverflag.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())

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

	StartupConfig <- startupConfig{
		Handler:       server.Handler,
		Authenticator: config.GenericConfig.Authentication.Authenticator,
	}

	return server.PrepareRun().Run(stopCh)
}

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

	if DefaultProxyDialerFn != nil {
		completedOptions.KubeletConfig.Dial = DefaultProxyDialerFn
	}

	kubeAPIServerConfig, insecureServingInfo, serviceResolver, pluginInitializer, admissionPostStartHook, err := CreateKubeAPIServerConfig(completedOptions, proxyTransport)
	if err != nil {
		return nil, 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(nil, kubeAPIServerConfig.GenericConfig.LoopbackClientConfig))
	if err != nil {
		return nil, nil, err
	}
	apiExtensionsServer, err := createAPIExtensionsServer(apiExtensionsConfig, genericapiserver.NewEmptyDelegate())
	if err != nil {
		return nil, nil, err
	}

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

	// otherwise go down the normal path of standing the aggregator up in front of the API server
	// this wires up openapi
	kubeAPIServer.GenericAPIServer.PrepareRun()

	// This will wire up openapi for extension api server
	apiExtensionsServer.GenericAPIServer.PrepareRun()

	// aggregator comes last in the chain
	aggregatorConfig, err := createAggregatorConfig(*kubeAPIServerConfig.GenericConfig, completedOptions.ServerRunOptions, kubeAPIServerConfig.ExtraConfig.VersionedInformers, serviceResolver, nil, pluginInitializer)
	if err != nil {
		return nil, 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, nil, err
	}

	if insecureServingInfo != nil {
		insecureHandlerChain := kubeserver.BuildInsecureHandlerChain(aggregatorServer.GenericAPIServer.UnprotectedHandler(), kubeAPIServerConfig.GenericConfig)
		if err := insecureServingInfo.Serve(insecureHandlerChain, kubeAPIServerConfig.GenericConfig.RequestTimeout, stopCh); err != nil {
			return nil, nil, err
		}
	}

	return kubeAPIServerConfig, aggregatorServer.GenericAPIServer, nil
}

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

	kubeAPIServer.GenericAPIServer.AddPostStartHookOrDie("start-kube-apiserver-admission-initializer", admissionPostStartHook)

	return kubeAPIServer, nil
}

// CreateNodeDialer creates the dialer infrastructure to connect to the nodes.
func CreateNodeDialer(s completedServerRunOptions) (*http.Transport, error) {
	proxyTLSClientConfig := &tls.Config{InsecureSkipVerify: true}
	proxyTransport := utilnet.SetTransportDefaults(&http.Transport{
		DialContext:     nil,
		TLSClientConfig: proxyTLSClientConfig,
	})
	return proxyTransport, nil
}

// CreateKubeAPIServerConfig creates all the resources for running the API server, but runs none of them
func CreateKubeAPIServerConfig(
	s completedServerRunOptions,
	proxyTransport *http.Transport,
) (
	config *master.Config,
	insecureServingInfo *genericapiserver.DeprecatedInsecureServingInfo,
	serviceResolver aggregatorapiserver.ServiceResolver,
	pluginInitializers []admission.PluginInitializer,
	admissionPostStartHook genericapiserver.PostStartHookFunc,
	lastErr error,
) {
	var genericConfig *genericapiserver.Config
	var storageFactory *serverstorage.DefaultStorageFactory
	var versionedInformers clientgoinformers.SharedInformerFactory
	genericConfig, versionedInformers, insecureServingInfo, serviceResolver, pluginInitializers, admissionPostStartHook, storageFactory, lastErr = buildGenericConfig(s.ServerRunOptions, proxyTransport)
	if lastErr != nil {
		return
	}

	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,
	})

	serviceIPRange, apiServerServiceIP, lastErr := master.DefaultServiceIPRange(s.ServiceClusterIPRange)
	if lastErr != nil {
		return
	}

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

			ServiceIPRange:       serviceIPRange,
			APIServerServiceIP:   apiServerServiceIP,
			APIServerServicePort: 443,

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

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

			ServiceAccountIssuer:        s.ServiceAccountIssuer,
			ServiceAccountMaxExpiration: s.ServiceAccountTokenMaxExpiration,

			VersionedInformers: versionedInformers,
		},
	}

	return
}

// 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,
	insecureServingInfo *genericapiserver.DeprecatedInsecureServingInfo,
	serviceResolver aggregatorapiserver.ServiceResolver,
	pluginInitializers []admission.PluginInitializer,
	admissionPostStartHook genericapiserver.PostStartHookFunc,
	storageFactory *serverstorage.DefaultStorageFactory,
	lastErr error,
) {
	genericConfig = genericapiserver.NewConfig(legacyscheme.Codecs)
	genericConfig.MergedResourceConfig = master.DefaultAPIResourceConfigSource()

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

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

	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, s.StorageSerialization)
	if err != nil {
		lastErr = err
		return
	}
	storageFactory, lastErr = completedStorageFactoryConfig.New()
	if lastErr != nil {
		return
	}
	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"

	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)

	genericConfig.Authentication.Authenticator, err = BuildAuthenticator(s, clientgoExternalClient, versionedInformers)
	if err != nil {
		lastErr = fmt.Errorf("invalid authentication config: %v", err)
		return
	}

	genericConfig.Authorization.Authorizer, genericConfig.RuleResolver, err = BuildAuthorizer(s, 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)
	}

	admissionConfig := &kubeapiserveradmission.Config{
		ExternalInformers:    versionedInformers,
		LoopbackClientConfig: genericConfig.LoopbackClientConfig,
		CloudConfigFile:      s.CloudProvider.CloudConfigFile,
	}
	serviceResolver = buildServiceResolver(s.EnableAggregatorRouting, genericConfig.LoopbackClientConfig.Host, versionedInformers)

	authInfoResolverWrapper := webhook.NewDefaultAuthenticationInfoResolverWrapper(proxyTransport, genericConfig.LoopbackClientConfig)

	lastErr = s.Audit.ApplyTo(
		genericConfig,
		genericConfig.LoopbackClientConfig,
		versionedInformers,
		serveroptions.NewProcessInfo("kube-apiserver", "kube-system"),
		&serveroptions.WebhookOptions{
			AuthInfoResolverWrapper: authInfoResolverWrapper,
			ServiceResolver:         serviceResolver,
		},
	)
	if lastErr != nil {
		return
	}

	pluginInitializers, admissionPostStartHook, err = admissionConfig.New(proxyTransport, serviceResolver)
	if err != nil {
		lastErr = fmt.Errorf("failed to create admission plugin initializer: %v", err)
		return
	}

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

	return
}

// BuildAuthenticator constructs the authenticator
func BuildAuthenticator(s *options.ServerRunOptions, extclient clientgoclientset.Interface, versionedInformer clientgoinformers.SharedInformerFactory) (authenticator.Request, error) {
	authenticatorConfig := s.Authentication.ToAuthenticationConfig()
	if s.Authentication.ServiceAccounts.Lookup {
		authenticatorConfig.ServiceAccountTokenGetter = serviceaccountcontroller.NewGetterFromClient(extclient)
	}

	return authenticatorConfig.New()
}

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

// 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
	}
	if err := kubeoptions.DefaultAdvertiseAddress(s.GenericServerRunOptions, s.InsecureServing.DeprecatedInsecureServingOptions); err != nil {
		return options, err
	}
	serviceIPRange, apiServerServiceIP, err := master.DefaultServiceIPRange(s.ServiceClusterIPRange)
	if err != nil {
		return options, fmt.Errorf("error determining service IP ranges: %v", err)
	}
	s.ServiceClusterIPRange = serviceIPRange
	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 oppurtunity 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 := certutil.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 serviceaccount max expiration must be between 1 hour to 2^32 seconds")
			}
		}

		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 {
		klog.V(2).Infof("Initializing cache sizes based on %dMB limit", s.GenericServerRunOptions.TargetRAMMB)
		sizes := cachesize.NewHeuristicWatchCacheSizes(s.GenericServerRunOptions.TargetRAMMB)
		if userSpecified, err := serveroptions.ParseWatchCacheSizes(s.Etcd.WatchCacheSizes); err == nil {
			for resource, size := range userSpecified {
				sizes[resource] = size
			}
		}
		s.Etcd.WatchCacheSizes, err = serveroptions.WriteWatchCacheSizes(sizes)
		if err != nil {
			return options, err
		}
	}

	// TODO: remove when we stop supporting the legacy group version.
	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 readCAorNil(file string) ([]byte, error) {
	if len(file) == 0 {
		return nil, nil
	}
	return ioutil.ReadFile(file)
}