kube-apiserver

Kubernetes API server 为 api 对象验证并配置数据，包括 pods、 services、 replicationcontrollers 和其它 api 对象。API Server 提供 REST 操作和到集群共享状态的前端，所有其他组件通过它进行交互

启动流程

kube-apiserver的启动入口路径为/cmd/kube-apiserver/apiserver.go:main()，主要作以下三件事：

• 生成APIServer启动命令

• 初始化log

• 运行APIServer命令

func main() {
	rand.Seed(time.Now().UnixNano())

	command := app.NewAPIServerCommand()

	// 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()
	logs.InitLogs()
	defer logs.FlushLogs()

	if err := command.Execute(); err != nil {
		fmt.Fprintf(os.Stderr, "error: %v\n", err)
		os.Exit(1)
	}
}

API Server Command配置

app.NewAPIServerCommand()方法定义在/cmd/kube-apiserver/app/server.go文件中，目的是创建一个cobra 命名对象。

// NewAPIServerCommand creates a *cobra.Command object with default parameters
func NewAPIServerCommand() *cobra.Command {
    // 创建一个新的NewServerRunOptions对象，并配置默认参数
	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.`,
        // 定义Run方法
		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, genericapiserver.SetupSignalHandler())
		},
	}

	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
}

ServerRunOptions配置

这个结构主要是关于一些命令行参数的解析配置，例如etcd与kubelet client端的参数配置等，该结构定义在/cmd/kube-apiserver/app/options/options.go文件中：

// NewServerRunOptions creates a new ServerRunOptions object with default parameters
func NewServerRunOptions() *ServerRunOptions {
    ...
}

// 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
	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
	ServiceAccountIssuer             serviceaccount.TokenGenerator
	ServiceAccountTokenMaxExpiration time.Duration
}

Run函数定义

主要完成以下操作：

• 设置默认options - Complelte(s)

• 验证options - completedOptions.Validate()

• 运行真正的Run方法 - Run(completedOptions, genericapiserver.SetupSignalHandler())

运行APIServer命令

执行上述定义的Run方法（路径为/cmd/kube-apiserver/app/server.go）：

// 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())

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

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

创建apiserver chain

路径为/cmd/kube-apiserver/app/server.go，主要完成以下操作：

• 创建NodeDialer - CreateNodeDialer(completedOptions)

• 创建kube-apiserver配置资源 - CreateKubeAPIServerConfig(completedOptions, nodeTunneler, proxyTransport)

• 创建扩展API配置 - CreateKubeAPIServerConfig(completedOptions, nodeTunneler, proxyTransport)和createAPIExtensionsServer(apiExtensionsConfig, genericapiserver.NewEmptyDelegate())

• 创建kube-apiserver实例 - CreateKubeAPIServer(kubeAPIServerConfig, apiExtensionsServer.GenericAPIServer, admissionPostStartHook)

• 运行准备阶段 - kubeAPIServer.GenericAPIServer.PrepareRun()和apiExtensionsServer.GenericAPIServer.PrepareRun()

• 创建Aggregator配置 - createAggregatorConfig()和createAggregatorServer()

运行kube-apiserver

当创建好kube-apiserver所需资源配置时，运行kube-apiserver实例：

server.PrepareRun().Run(stopCh)

流程概述

转自：https://xigang.github.io/2019/11/23/kube-apisever/