以下代码分析基于 kubernetes v1.12.0 版本。



├── apiserver.go   # kube-apiserver的main入口
└── app
    ├── aggregator.go
    ├── apiextensions.go
    ├── options  # 初始化kube-apiserver使用到的option
    │   ├── options.go     # 包括:NewServerRunOptions、Flags等
    │   ├── options_test.go
    │   └── validation.go
    ├── server.go   # 包括:NewAPIServerCommand、Run、CreateServerChain、Complete等

1. Main


func main() {

    command := app.NewAPIServerCommand(server.SetupSignalHandler())

    // TODO: once we switch everything over to Cobra commands, we can go back to calling
    // utilflag.InitFlags() (by removing its pflag.Parse() call). For now, we have to set the
    // normalize func and add the go flag set by hand.
    // utilflag.InitFlags()
    defer logs.FlushLogs()

    if err := command.Execute(); err != nil {
        fmt.Fprintf(os.Stderr, "error: %v\n", err)


// 初始化APIServerCommand
command := app.NewAPIServerCommand(server.SetupSignalHandler())
// 执行Execute
err := command.Execute()

2. NewAPIServerCommand



  • 构造option
  • 添加Flags
  • 执行Run函数



// 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 {

            // 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()
    for _, f := range namedFlagSets.FlagSets {

    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


// 构造option
s := options.NewServerRunOptions()
// 添加flags
fs := cmd.Flags()
namedFlagSets := s.Flags()
for _, f := range namedFlagSets.FlagSets {
// set default options
completedOptions, err := Complete(s)
// Run
Run(completedOptions, stopCh)

3. NewServerRunOptions


3.1. ServerRunOptions


  • GenericServerRunOptions
  • Etcd
  • SecureServing
  • KubeletConfig
  • // ServerRunOptions runs a kubernetes api server.
    type ServerRunOptions struct {
    GenericServerRunOptions *genericoptions.ServerRunOptions
    Etcd                    *genericoptions.EtcdOptions
    SecureServing           *genericoptions.SecureServingOptionsWithLoopback
    InsecureServing         *genericoptions.DeprecatedInsecureServingOptionsWithLoopback
    Audit                   *genericoptions.AuditOptions
    Features                *genericoptions.FeatureOptions
    Admission               *kubeoptions.AdmissionOptions
    Authentication          *kubeoptions.BuiltInAuthenticationOptions
    Authorization           *kubeoptions.BuiltInAuthorizationOptions
    CloudProvider           *kubeoptions.CloudProviderOptions
    StorageSerialization    *kubeoptions.StorageSerializationOptions
    APIEnablement           *genericoptions.APIEnablementOptions
    AllowPrivileged           bool
    EnableLogsHandler         bool
    EventTTL                  time.Duration
    KubeletConfig             kubeletclient.KubeletClientConfig
    KubernetesServiceNodePort int
    MaxConnectionBytesPerSec  int64
    ServiceClusterIPRange     net.IPNet // TODO: make this a list
    ServiceNodePortRange      utilnet.PortRange
    SSHKeyfile                string
    SSHUser                   string
    ProxyClientCertFile string
    ProxyClientKeyFile  string
    EnableAggregatorRouting bool
    MasterCount            int
    EndpointReconcilerType string
    ServiceAccountSigningKeyFile string

3.2. NewServerRunOptions


// NewServerRunOptions creates a new ServerRunOptions object with default parameters
func NewServerRunOptions() *ServerRunOptions {
    s := ServerRunOptions{
        GenericServerRunOptions: genericoptions.NewServerRunOptions(),
        Etcd:                 genericoptions.NewEtcdOptions(storagebackend.NewDefaultConfig(kubeoptions.DefaultEtcdPathPrefix, nil)),
        SecureServing:        kubeoptions.NewSecureServingOptions(),
        InsecureServing:      kubeoptions.NewInsecureServingOptions(),
        Audit:                genericoptions.NewAuditOptions(),
        Features:             genericoptions.NewFeatureOptions(),
        Admission:            kubeoptions.NewAdmissionOptions(),
        Authentication:       kubeoptions.NewBuiltInAuthenticationOptions().WithAll(),
        Authorization:        kubeoptions.NewBuiltInAuthorizationOptions(),
        CloudProvider:        kubeoptions.NewCloudProviderOptions(),
        StorageSerialization: kubeoptions.NewStorageSerializationOptions(),
        APIEnablement:        genericoptions.NewAPIEnablementOptions(),

        EnableLogsHandler:      true,
        EventTTL:               1 * time.Hour,
        MasterCount:            1,
        EndpointReconcilerType: string(reconcilers.LeaseEndpointReconcilerType),
        KubeletConfig: kubeletclient.KubeletClientConfig{
            Port:         ports.KubeletPort,
            ReadOnlyPort: ports.KubeletReadOnlyPort,
            PreferredAddressTypes: []string{
                // --override-hostname

                // internal, preferring DNS if reported

                // external, preferring DNS if reported
            EnableHttps: true,
            HTTPTimeout: time.Duration(5) * time.Second,
        ServiceNodePortRange: kubeoptions.DefaultServiceNodePortRange,
    s.ServiceClusterIPRange = kubeoptions.DefaultServiceIPCIDR

    // Overwrite the default for storage data format.
    s.Etcd.DefaultStorageMediaType = "application/vnd.kubernetes.protobuf"

    return &s

3.3. Complete



// 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)
        glog.Infof("external host was not specified, using %v", s.GenericServerRunOptions.ExternalHost)


    // 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 {
                glog.Warning("No TLS key provided, service account token authentication disabled")

    if s.Etcd.StorageConfig.DeserializationCacheSize == 0 {
        // When size of cache is not explicitly set, estimate its size based on
        // target memory usage.
        glog.V(2).Infof("Initializing deserialization cache size based on %dMB limit", s.GenericServerRunOptions.TargetRAMMB)

        // This is the heuristics that from memory capacity is trying to infer
        // the maximum number of nodes in the cluster and set cache sizes based
        // on that value.
        // From our documentation, we officially recommend 120GB machines for
        // 2000 nodes, and we scale from that point. Thus we assume ~60MB of
        // capacity per node.
        // TODO: We may consider deciding that some percentage of memory will
        // be used for the deserialization cache and divide it by the max object
        // size to compute its size. We may even go further and measure
        // collective sizes of the objects in the cache.
        clusterSize := s.GenericServerRunOptions.TargetRAMMB / 60
        s.Etcd.StorageConfig.DeserializationCacheSize = 25 * clusterSize
        if s.Etcd.StorageConfig.DeserializationCacheSize < 1000 {
            s.Etcd.StorageConfig.DeserializationCacheSize = 1000
    if s.Etcd.EnableWatchCache {
        glog.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

3. AddFlagSet



fs := cmd.Flags()
namedFlagSets := s.Flags()
for _, f := range namedFlagSets.FlagSets {

3.1. Flags



// Flags returns flags for a specific APIServer by section name
func (s *ServerRunOptions) Flags() (fss apiserverflag.NamedFlagSets) {
    // Add the generic flags.
    s.SecureServing.AddFlags(fss.FlagSet("secure serving"))
    s.InsecureServing.AddFlags(fss.FlagSet("insecure serving"))
    s.InsecureServing.AddUnqualifiedFlags(fss.FlagSet("insecure serving")) // TODO: remove it until kops stops using `--address`
    s.CloudProvider.AddFlags(fss.FlagSet("cloud provider"))
    s.APIEnablement.AddFlags(fss.FlagSet("api enablement"))

    // Note: the weird ""+ in below lines seems to be the only way to get gofmt to
    // arrange these text blocks sensibly. Grrr.
    fs := fss.FlagSet("misc")
    fs.DurationVar(&s.EventTTL, "event-ttl", s.EventTTL,
        "Amount of time to retain events.")

    fs.BoolVar(&s.AllowPrivileged, "allow-privileged", s.AllowPrivileged,
        "If true, allow privileged containers. [default=false]")

    fs.BoolVar(&s.EnableLogsHandler, "enable-logs-handler", s.EnableLogsHandler,
        "If true, install a /logs handler for the apiserver logs.")

    // Deprecated in release 1.9
    fs.StringVar(&s.SSHUser, "ssh-user", s.SSHUser,
        "If non-empty, use secure SSH proxy to the nodes, using this user name")
    fs.MarkDeprecated("ssh-user", "This flag will be removed in a future version.")

    // Deprecated in release 1.9
    fs.StringVar(&s.SSHKeyfile, "ssh-keyfile", s.SSHKeyfile,
        "If non-empty, use secure SSH proxy to the nodes, using this user keyfile")
    fs.MarkDeprecated("ssh-keyfile", "This flag will be removed in a future version.")

    fs.Int64Var(&s.MaxConnectionBytesPerSec, "max-connection-bytes-per-sec", s.MaxConnectionBytesPerSec, ""+
        "If non-zero, throttle each user connection to this number of bytes/sec. "+
        "Currently only applies to long-running requests.")

    fs.IntVar(&s.MasterCount, "apiserver-count", s.MasterCount,
        "The number of apiservers running in the cluster, must be a positive number. (In use when --endpoint-reconciler-type=master-count is enabled.)")

    fs.StringVar(&s.EndpointReconcilerType, "endpoint-reconciler-type", string(s.EndpointReconcilerType),
        "Use an endpoint reconciler ("+strings.Join(reconcilers.AllTypes.Names(), ", ")+")")

    // See #14282 for details on how to test/try this option out.
    // TODO: remove this comment once this option is tested in CI.
    fs.IntVar(&s.KubernetesServiceNodePort, "kubernetes-service-node-port", s.KubernetesServiceNodePort, ""+
        "If non-zero, the Kubernetes master service (which apiserver creates/maintains) will be "+
        "of type NodePort, using this as the value of the port. If zero, the Kubernetes master "+
        "service will be of type ClusterIP.")

    fs.IPNetVar(&s.ServiceClusterIPRange, "service-cluster-ip-range", s.ServiceClusterIPRange, ""+
        "A CIDR notation IP range from which to assign service cluster IPs. This must not "+
        "overlap with any IP ranges assigned to nodes for pods.")

    fs.Var(&s.ServiceNodePortRange, "service-node-port-range", ""+
        "A port range to reserve for services with NodePort visibility. "+
        "Example: '30000-32767'. Inclusive at both ends of the range.")

    // Kubelet related flags:
    fs.BoolVar(&s.KubeletConfig.EnableHttps, "kubelet-https", s.KubeletConfig.EnableHttps,
        "Use https for kubelet connections.")

    fs.StringSliceVar(&s.KubeletConfig.PreferredAddressTypes, "kubelet-preferred-address-types", s.KubeletConfig.PreferredAddressTypes,
        "List of the preferred NodeAddressTypes to use for kubelet connections.")

    fs.UintVar(&s.KubeletConfig.Port, "kubelet-port", s.KubeletConfig.Port,
        "DEPRECATED: kubelet port.")
    fs.MarkDeprecated("kubelet-port", "kubelet-port is deprecated and will be removed.")

    fs.UintVar(&s.KubeletConfig.ReadOnlyPort, "kubelet-read-only-port", s.KubeletConfig.ReadOnlyPort,
        "DEPRECATED: kubelet port.")

    fs.DurationVar(&s.KubeletConfig.HTTPTimeout, "kubelet-timeout", s.KubeletConfig.HTTPTimeout,
        "Timeout for kubelet operations.")

    fs.StringVar(&s.KubeletConfig.CertFile, "kubelet-client-certificate", s.KubeletConfig.CertFile,
        "Path to a client cert file for TLS.")

    fs.StringVar(&s.KubeletConfig.KeyFile, "kubelet-client-key", s.KubeletConfig.KeyFile,
        "Path to a client key file for TLS.")

    fs.StringVar(&s.KubeletConfig.CAFile, "kubelet-certificate-authority", s.KubeletConfig.CAFile,
        "Path to a cert file for the certificate authority.")

    // TODO: delete this flag in 1.13
    repair := false
    fs.BoolVar(&repair, "repair-malformed-updates", false, "deprecated")
    fs.MarkDeprecated("repair-malformed-updates", "This flag will be removed in a future version")

    fs.StringVar(&s.ProxyClientCertFile, "proxy-client-cert-file", s.ProxyClientCertFile, ""+
        "Client certificate used to prove the identity of the aggregator or kube-apiserver "+
        "when it must call out during a request. This includes proxying requests to a user "+
        "api-server and calling out to webhook admission plugins. It is expected that this "+
        "cert includes a signature from the CA in the --requestheader-client-ca-file flag. "+
        "That CA is published in the 'extension-apiserver-authentication' configmap in "+
        "the kube-system namespace. Components receiving calls from kube-aggregator should "+
        "use that CA to perform their half of the mutual TLS verification.")
    fs.StringVar(&s.ProxyClientKeyFile, "proxy-client-key-file", s.ProxyClientKeyFile, ""+
        "Private key for the client certificate used to prove the identity of the aggregator or kube-apiserver "+
        "when it must call out during a request. This includes proxying requests to a user "+
        "api-server and calling out to webhook admission plugins.")

    fs.BoolVar(&s.EnableAggregatorRouting, "enable-aggregator-routing", s.EnableAggregatorRouting,
        "Turns on aggregator routing requests to endpoints IP rather than cluster IP.")

    fs.StringVar(&s.ServiceAccountSigningKeyFile, "service-account-signing-key-file", s.ServiceAccountSigningKeyFile, ""+
        "Path to the file that contains the current private key of the service account token issuer. The issuer will sign issued ID tokens with this private key. (Requires the 'TokenRequest' feature gate.)")

    return fss

4. Run



  1. 构造一个聚合的server结构体。
  2. 执行PrepareRun。
  3. 最终执行Run。


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

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

    return server.PrepareRun().Run(stopCh)

4.1. CreateServerChain



  1. 首先生成config对象,包括kubeAPIServerConfigapiExtensionsConfig
  2. 再通过config生成server对象,包括apiExtensionsServerkubeAPIServer
  3. 执行apiExtensionsServerkubeAPIServerPrepareRun部分。
  4. 生成聚合的config对象aggregatorConfig
  5. 基于aggregatorConfigkubeAPIServerapiExtensionsServer生成聚合的serveraggregatorServer


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

    kubeAPIServerConfig, insecureServingInfo, serviceResolver, pluginInitializer, admissionPostStartHook, 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)
    if err != nil {
        return nil, err
    apiExtensionsServer, err := createAPIExtensionsServer(apiExtensionsConfig, genericapiserver.NewEmptyDelegate())
    if err != nil {
        return nil, err

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

    // otherwise go down the normal path of standing the aggregator up in front of the API server
    // this wires up openapi

    // This will wire up openapi for extension api server

    // 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

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

    return aggregatorServer.GenericAPIServer, nil

4.2. PrepareRun



// PrepareRun does post API installation setup steps.
func (s *GenericAPIServer) PrepareRun() preparedGenericAPIServer {
    if s.swaggerConfig != nil {
        routes.Swagger{Config: s.swaggerConfig}.Install(s.Handler.GoRestfulContainer)
    if s.openAPIConfig != nil {
            Config: s.openAPIConfig,
        }.Install(s.Handler.GoRestfulContainer, s.Handler.NonGoRestfulMux)


    // Register audit backend preShutdownHook.
    if s.AuditBackend != nil {
        s.AddPreShutdownHook("audit-backend", func() error {
            return nil

    return preparedGenericAPIServer{s}

4.3. preparedGenericAPIServer.Run

preparedGenericAPIServer.Run运行一个安全的http server。具体的实现逻辑待后续文章分析。


// Run spawns the secure http server. It only returns if stopCh is closed
// or the secure port cannot be listened on initially.
func (s preparedGenericAPIServer) Run(stopCh <-chan struct{}) error {
    err := s.NonBlockingRun(stopCh)
    if err != nil {
        return err


    err = s.RunPreShutdownHooks()
    if err != nil {
        return err

    // Wait for all requests to finish, which are bounded by the RequestTimeout variable.

    return nil


err := s.NonBlockingRun(stopCh)

preparedGenericAPIServer.Run主要是调用NonBlockingRun函数,最终运行一个http server。该部分逻辑待后续文章分析。

5. 总结


  • 构造option参数,提供给执行主体(例如 本文的server)作为配置参数使用。
  • 添加Flags,主要用来通过传入的flags参数最终解析成option中使用的结构体属性。
  • 执行Run函数,执行主体的运行逻辑部分(核心部分)。


  1. 构造一个聚合的server结构体。
  2. 执行PrepareRun。
  3. 最终执行preparedGenericAPIServer.Run。

preparedGenericAPIServer.Run主要是调用NonBlockingRun函数,最终运行一个http server。NonBlockingRun的具体逻辑待后续文章再单独分析。


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