kubelet源码分析（一）之 NewKubeletCommand

以下代码分析基于 kubernetes v1.12.0 版本。

本文主要分析 https://github.com/kubernetes/kubernetes/tree/v1.12.0/cmd/kubelet 部分的代码。

本文主要分析 kubernetes/cmd/kubelet部分，该部分主要涉及kubelet的参数解析，及初始化和构造相关的依赖组件（主要在kubeDeps结构体中），并没有kubelet运行的详细逻辑，该部分位于kubernetes/pkg/kubelet模块，待后续文章分析。

kubelet的cmd代码目录结构如下：

  1. kubelet
  2. ├── app
  3. │   ├── auth.go
  4. │   ├── init_others.go
  5. │   ├── init_windows.go
  6. │   ├── options              # 包括kubelet使用到的option
  7. │   │   ├── container_runtime.go
  8. │   │   ├── globalflags.go
  9. │   │   ├── globalflags_linux.go
  10. │   │   ├── globalflags_other.go
  11. │   │   ├── options.go     # 包括KubeletFlags、AddFlags、AddKubeletConfigFlags等
  12. │   │   ├── osflags_others.go
  13. │   │   └── osflags_windows.go
  14. │   ├── plugins.go
  15. │   ├── server.go # 包括NewKubeletCommand、Run、RunKubelet、CreateAndInitKubelet、startKubelet等
  16. │   ├── server_linux.go
  17. │   └── server_unsupported.go
  18. └── kubelet.go              # kubelet的main入口函数

1. Main 函数

kubelet的入口函数Main 函数，具体代码参考：https://github.com/kubernetes/kubernetes/blob/v1.12.0/cmd/kubelet/kubelet.go。 

  1. func main() {
  2.     rand.Seed(time.Now().UTC().UnixNano())
  4.     command := app.NewKubeletCommand(server.SetupSignalHandler())
  5.     logs.InitLogs()
  6.     defer logs.FlushLogs()
  8.     if err := command.Execute(); err != nil {
  9.         fmt.Fprintf(os.Stderr, "%v\n", err)
  10.         os.Exit(1)
  11.     }
  12. }

kubelet代码主要采用了Cobra命令行框架，核心代码如下：

  1. // 初始化命令行
  2. command := app.NewKubeletCommand(server.SetupSignalHandler())
  3. // 执行Execute
  4. err := command.Execute()

2. NewKubeletCommand

NewKubeletCommand基于参数创建了一个*cobra.Command对象。其中核心部分代码为参数解析部分和Run函数。

  1. // NewKubeletCommand creates a *cobra.Command object with default parameters
  2. func NewKubeletCommand(stopCh <-chan struct{}) *cobra.Command {
  3.     ...
  4.     cmd := &cobra.Command{
  5.         Use: componentKubelet,
  6.         Long: `...`,
  7.         // The Kubelet has special flag parsing requirements to enforce flag precedence rules,
  8.         // so we do all our parsing manually in Run, below.
  9.         // DisableFlagParsing=true provides the full set of flags passed to the kubelet in the
  10.         // `args` arg to Run, without Cobra's interference.
  11.         DisableFlagParsing: true,
  12.         Run: func(cmd *cobra.Command, args []string) {
  13.             ...
  14.             // run the kubelet
  15.             glog.V(5).Infof("KubeletConfiguration: %#v", kubeletServer.KubeletConfiguration)
  16.             if err := Run(kubeletServer, kubeletDeps, stopCh); err != nil {
  17.                 glog.Fatal(err)
  18.             }
  19.         },
  20.     }
  21.     ...
  22.     return cmd
  23. }

2.1. 参数解析

kubelet开启了DisableFlagParsing参数，没有使用Cobra框架中的默认参数解析，而是自定义参数解析。

2.1.1. 初始化参数和配置

初始化参数解析，初始化cleanFlagSet，kubeletFlags，kubeletConfig。

  1. cleanFlagSet := pflag.NewFlagSet(componentKubelet, pflag.ContinueOnError)
  2. cleanFlagSet.SetNormalizeFunc(flag.WordSepNormalizeFunc)
  3. kubeletFlags := options.NewKubeletFlags()
  4. kubeletConfig, err := options.NewKubeletConfiguration()

2.1.2. 打印帮助信息和版本信息

如果输入非法参数则打印使用帮助信息。

  1. // initial flag parse, since we disable cobra's flag parsing
  2. if err := cleanFlagSet.Parse(args); err != nil {
  3.     cmd.Usage()
  4.     glog.Fatal(err)
  5. }
  7. // check if there are non-flag arguments in the command line
  8. cmds := cleanFlagSet.Args()
  9. if len(cmds) > 0 {
  10.     cmd.Usage()
  11.     glog.Fatalf("unknown command: %s", cmds[0])
  12. }

遇到help和version参数则打印相关内容并退出。

  1. // short-circuit on help
  2. help, err := cleanFlagSet.GetBool("help")
  3. if err != nil {
  4.     glog.Fatal(`"help" flag is non-bool, programmer error, please correct`)
  5. }
  6. if help {
  7.     cmd.Help()
  8.     return
  9. }
  11. // short-circuit on verflag
  12. verflag.PrintAndExitIfRequested()
  13. utilflag.PrintFlags(cleanFlagSet)

2.1.3. kubelet config

加载并校验kubelet config。其中包括校验初始化的kubeletFlags，并从kubeletFlags的KubeletConfigFile参数获取kubelet config的内容。

  1. // set feature gates from initial flags-based config
  2. if err := utilfeature.DefaultFeatureGate.SetFromMap(kubeletConfig.FeatureGates); err != nil {
  3.     glog.Fatal(err)
  4. }
  6. // validate the initial KubeletFlags
  7. if err := options.ValidateKubeletFlags(kubeletFlags); err != nil {
  8.     glog.Fatal(err)
  9. }
  11. if kubeletFlags.ContainerRuntime == "remote" && cleanFlagSet.Changed("pod-infra-container-image") {
  12.     glog.Warning("Warning: For remote container runtime, --pod-infra-container-image is ignored in kubelet, which should be set in that remote runtime instead")
  13. }
  15. // load kubelet config file, if provided
  16. if configFile := kubeletFlags.KubeletConfigFile; len(configFile) > 0 {
  17.     kubeletConfig, err = loadConfigFile(configFile)
  18.     if err != nil {
  19.         glog.Fatal(err)
  20.     }
  21.     // We must enforce flag precedence by re-parsing the command line into the new object.
  22.     // This is necessary to preserve backwards-compatibility across binary upgrades.
  23.     // See issue #56171 for more details.
  24.     if err := kubeletConfigFlagPrecedence(kubeletConfig, args); err != nil {
  25.         glog.Fatal(err)
  26.     }
  27.     // update feature gates based on new config
  28.     if err := utilfeature.DefaultFeatureGate.SetFromMap(kubeletConfig.FeatureGates); err != nil {
  29.         glog.Fatal(err)
  30.     }
  31. }
  33. // We always validate the local configuration (command line + config file).
  34. // This is the default "last-known-good" config for dynamic config, and must always remain valid.
  35. if err := kubeletconfigvalidation.ValidateKubeletConfiguration(kubeletConfig); err != nil {
  36.     glog.Fatal(err)
  37. }

2.1.4. dynamic kubelet config

如果开启使用动态kubelet的配置，则由动态配置文件替换kubelet配置文件。

  1. // use dynamic kubelet config, if enabled
  2. var kubeletConfigController *dynamickubeletconfig.Controller
  3. if dynamicConfigDir := kubeletFlags.DynamicConfigDir.Value(); len(dynamicConfigDir) > 0 {
  4.     var dynamicKubeletConfig *kubeletconfiginternal.KubeletConfiguration
  5.     dynamicKubeletConfig, kubeletConfigController, err = BootstrapKubeletConfigController(dynamicConfigDir,
  6.         func(kc *kubeletconfiginternal.KubeletConfiguration) error {
  7.             // Here, we enforce flag precedence inside the controller, prior to the controller's validation sequence,
  8.             // so that we get a complete validation at the same point where we can decide to reject dynamic config.
  9.             // This fixes the flag-precedence component of issue #63305.
  10.             // See issue #56171 for general details on flag precedence.
  11.             return kubeletConfigFlagPrecedence(kc, args)
  12.         })
  13.     if err != nil {
  14.         glog.Fatal(err)
  15.     }
  16.     // If we should just use our existing, local config, the controller will return a nil config
  17.     if dynamicKubeletConfig != nil {
  18.         kubeletConfig = dynamicKubeletConfig
  19.         // Note: flag precedence was already enforced in the controller, prior to validation,
  20.         // by our above transform function. Now we simply update feature gates from the new config.
  21.         if err := utilfeature.DefaultFeatureGate.SetFromMap(kubeletConfig.FeatureGates); err != nil {
  22.             glog.Fatal(err)
  23.         }
  24.     }
  25. }

总结：以上通过对各种特定参数的解析，最终生成kubeletFlags和kubeletConfig两个重要的参数对象，用来构造kubeletServer和其他需求。

2.2. 初始化kubeletServer和kubeletDeps

2.2.1. kubeletServer

  1. // construct a KubeletServer from kubeletFlags and kubeletConfig
  2. kubeletServer := &options.KubeletServer{
  3.     KubeletFlags:         *kubeletFlags,
  4.     KubeletConfiguration: *kubeletConfig,
  5. }

2.2.2. kubeletDeps

  1. // use kubeletServer to construct the default KubeletDeps
  2. kubeletDeps, err := UnsecuredDependencies(kubeletServer)
  3. if err != nil {
  4.     glog.Fatal(err)
  5. }
  7. // add the kubelet config controller to kubeletDeps
  8. kubeletDeps.KubeletConfigController = kubeletConfigController

2.2.3. docker shim

如果开启了docker shim参数，则执行RunDockershim。

  1. // start the experimental docker shim, if enabled
  2. if kubeletServer.KubeletFlags.ExperimentalDockershim {
  3.     if err := RunDockershim(&kubeletServer.KubeletFlags, kubeletConfig, stopCh); err != nil {
  4.         glog.Fatal(err)
  5.     }
  6.     return
  7. }

2.3. AddFlags

  1. // keep cleanFlagSet separate, so Cobra doesn't pollute it with the global flags
  2. kubeletFlags.AddFlags(cleanFlagSet)
  3. options.AddKubeletConfigFlags(cleanFlagSet, kubeletConfig)
  4. options.AddGlobalFlags(cleanFlagSet)
  5. cleanFlagSet.BoolP("help", "h", false, fmt.Sprintf("help for %s", cmd.Name()))
  7. // ugly, but necessary, because Cobra's default UsageFunc and HelpFunc pollute the flagset with global flags
  8. const usageFmt = "Usage:\n  %s\n\nFlags:\n%s"
  9. cmd.SetUsageFunc(func(cmd *cobra.Command) error {
  10.     fmt.Fprintf(cmd.OutOrStderr(), usageFmt, cmd.UseLine(), cleanFlagSet.FlagUsagesWrapped(2))
  11.     return nil
  12. })
  13. cmd.SetHelpFunc(func(cmd *cobra.Command, args []string) {
  14.     fmt.Fprintf(cmd.OutOrStdout(), "%s\n\n"+usageFmt, cmd.Long, cmd.UseLine(), cleanFlagSet.FlagUsagesWrapped(2))
  15. })

其中：

2.4. 运行kubelet

运行kubelet并且不退出。由Run函数进入后续的操作。

  1. // run the kubelet
  2. glog.V(5).Infof("KubeletConfiguration: %#v", kubeletServer.KubeletConfiguration)
  3. if err := Run(kubeletServer, kubeletDeps, stopCh); err != nil {
  4.     glog.Fatal(err)
  5. }

3. Run

  1. // Run runs the specified KubeletServer with the given Dependencies. This should never exit.
  2. // The kubeDeps argument may be nil - if so, it is initialized from the settings on KubeletServer.
  3. // Otherwise, the caller is assumed to have set up the Dependencies object and a default one will
  4. // not be generated.
  5. func Run(s *options.KubeletServer, kubeDeps *kubelet.Dependencies, stopCh <-chan struct{}) error {
  6.     // To help debugging, immediately log version
  7.     glog.Infof("Version: %+v", version.Get())
  8.     if err := initForOS(s.KubeletFlags.WindowsService); err != nil {
  9.         return fmt.Errorf("failed OS init: %v", err)
  10.     }
  11.     if err := run(s, kubeDeps, stopCh); err != nil {
  12.         return fmt.Errorf("failed to run Kubelet: %v", err)
  13.     }
  14.     return nil
  15. }

当运行环境是Windows的时候，初始化操作，但是该操作为空，只是预留。具体执行run(s, kubeDeps, stopCh)函数。

3.1. 构造kubeDeps

3.1.1. clientConfig

创建clientConfig，该对象用来创建各种的kubeDeps属性中包含的client。

  1. clientConfig, err := createAPIServerClientConfig(s)
  2. if err != nil {
  3.     return fmt.Errorf("invalid kubeconfig: %v", err)
  4. }

3.1.2. kubeClient

  1. kubeClient, err = clientset.NewForConfig(clientConfig)
  2. if err != nil {
  3.     glog.Warningf("New kubeClient from clientConfig error: %v", err)
  4. } else if kubeClient.CertificatesV1beta1() != nil && clientCertificateManager != nil {
  5.     glog.V(2).Info("Starting client certificate rotation.")
  6.     clientCertificateManager.SetCertificateSigningRequestClient(kubeClient.CertificatesV1beta1().CertificateSigningRequests())
  7.     clientCertificateManager.Start()
  8. }

3.1.3. dynamicKubeClient

  1. dynamicKubeClient, err = dynamic.NewForConfig(clientConfig)
  2. if err != nil {
  3.     glog.Warningf("Failed to initialize dynamic KubeClient: %v", err)
  4. }

3.1.4. eventClient

  1. // make a separate client for events
  2. eventClientConfig := *clientConfig
  3. eventClientConfig.QPS = float32(s.EventRecordQPS)
  4. eventClientConfig.Burst = int(s.EventBurst)
  5. eventClient, err = v1core.NewForConfig(&eventClientConfig)
  6. if err != nil {
  7.     glog.Warningf("Failed to create API Server client for Events: %v", err)
  8. }

3.1.5. heartbeatClient

  1. // make a separate client for heartbeat with throttling disabled and a timeout attached
  2. heartbeatClientConfig := *clientConfig
  3. heartbeatClientConfig.Timeout = s.KubeletConfiguration.NodeStatusUpdateFrequency.Duration
  4. // if the NodeLease feature is enabled, the timeout is the minimum of the lease duration and status update frequency
  5. if utilfeature.DefaultFeatureGate.Enabled(features.NodeLease) {
  6.     leaseTimeout := time.Duration(s.KubeletConfiguration.NodeLeaseDurationSeconds) * time.Second
  7.     if heartbeatClientConfig.Timeout > leaseTimeout {
  8.         heartbeatClientConfig.Timeout = leaseTimeout
  9.     }
  10. }
  11. heartbeatClientConfig.QPS = float32(-1)
  12. heartbeatClient, err = clientset.NewForConfig(&heartbeatClientConfig)
  13. if err != nil {
  14.     glog.Warningf("Failed to create API Server client for heartbeat: %v", err)
  15. }

3.1.6. csiClient

  1. // csiClient works with CRDs that support json only
  2. clientConfig.ContentType = "application/json"
  3. csiClient, err := csiclientset.NewForConfig(clientConfig)
  4. if err != nil {
  5.     glog.Warningf("Failed to create CSI API client: %v", err)
  6. }

client赋值

  1. kubeDeps.KubeClient = kubeClient
  2. kubeDeps.DynamicKubeClient = dynamicKubeClient
  3. if heartbeatClient != nil {
  4.     kubeDeps.HeartbeatClient = heartbeatClient
  5.     kubeDeps.OnHeartbeatFailure = closeAllConns
  6. }
  7. if eventClient != nil {
  8.     kubeDeps.EventClient = eventClient
  9. }
  10. kubeDeps.CSIClient = csiClient

3.1.7. CAdvisorInterface

  1. if kubeDeps.CAdvisorInterface == nil {
  2.     imageFsInfoProvider := cadvisor.NewImageFsInfoProvider(s.ContainerRuntime, s.RemoteRuntimeEndpoint)
  3.     kubeDeps.CAdvisorInterface, err = cadvisor.New(imageFsInfoProvider, s.RootDirectory, cadvisor.UsingLegacyCadvisorStats(s.ContainerRuntime, s.RemoteRuntimeEndpoint))
  4.     if err != nil {
  5.         return err
  6.     }
  7. }

3.1.8. ContainerManager

  1. if kubeDeps.ContainerManager == nil {
  2.     if s.CgroupsPerQOS && s.CgroupRoot == "" {
  3.         glog.Infof("--cgroups-per-qos enabled, but --cgroup-root was not specified.  defaulting to /")
  4.         s.CgroupRoot = "/"
  5.     }
  6.     kubeReserved, err := parseResourceList(s.KubeReserved)
  7.     if err != nil {
  8.         return err
  9.     }
  10.     systemReserved, err := parseResourceList(s.SystemReserved)
  11.     if err != nil {
  12.         return err
  13.     }
  14.     var hardEvictionThresholds []evictionapi.Threshold
  15.     // If the user requested to ignore eviction thresholds, then do not set valid values for hardEvictionThresholds here.
  16.     if !s.ExperimentalNodeAllocatableIgnoreEvictionThreshold {
  17.         hardEvictionThresholds, err = eviction.ParseThresholdConfig([]string{}, s.EvictionHard, nil, nil, nil)
  18.         if err != nil {
  19.             return err
  20.         }
  21.     }
  22.     experimentalQOSReserved, err := cm.ParseQOSReserved(s.QOSReserved)
  23.     if err != nil {
  24.         return err
  25.     }
  27.     devicePluginEnabled := utilfeature.DefaultFeatureGate.Enabled(features.DevicePlugins)
  29.     kubeDeps.ContainerManager, err = cm.NewContainerManager(
  30.         kubeDeps.Mounter,
  31.         kubeDeps.CAdvisorInterface,
  32.         cm.NodeConfig{
  33.             RuntimeCgroupsName:    s.RuntimeCgroups,
  34.             SystemCgroupsName:     s.SystemCgroups,
  35.             KubeletCgroupsName:    s.KubeletCgroups,
  36.             ContainerRuntime:      s.ContainerRuntime,
  37.             CgroupsPerQOS:         s.CgroupsPerQOS,
  38.             CgroupRoot:            s.CgroupRoot,
  39.             CgroupDriver:          s.CgroupDriver,
  40.             KubeletRootDir:        s.RootDirectory,
  41.             ProtectKernelDefaults: s.ProtectKernelDefaults,
  42.             NodeAllocatableConfig: cm.NodeAllocatableConfig{
  43.                 KubeReservedCgroupName:   s.KubeReservedCgroup,
  44.                 SystemReservedCgroupName: s.SystemReservedCgroup,
  45.                 EnforceNodeAllocatable:   sets.NewString(s.EnforceNodeAllocatable...),
  46.                 KubeReserved:             kubeReserved,
  47.                 SystemReserved:           systemReserved,
  48.                 HardEvictionThresholds:   hardEvictionThresholds,
  49.             },
  50.             QOSReserved:                           *experimentalQOSReserved,
  51.             ExperimentalCPUManagerPolicy:          s.CPUManagerPolicy,
  52.             ExperimentalCPUManagerReconcilePeriod: s.CPUManagerReconcilePeriod.Duration,
  53.             ExperimentalPodPidsLimit:              s.PodPidsLimit,
  54.             EnforceCPULimits:                      s.CPUCFSQuota,
  55.             CPUCFSQuotaPeriod:                     s.CPUCFSQuotaPeriod.Duration,
  56.         },
  57.         s.FailSwapOn,
  58.         devicePluginEnabled,
  59.         kubeDeps.Recorder)
  61.     if err != nil {
  62.         return err
  63.     }
  64. }

3.1.9. oomAdjuster

  1. // TODO(vmarmol): Do this through container config.
  2. oomAdjuster := kubeDeps.OOMAdjuster
  3. if err := oomAdjuster.ApplyOOMScoreAdj(0, int(s.OOMScoreAdj)); err != nil {
  4.     glog.Warning(err)
  5. }

3.2. Health check

  1. if s.HealthzPort > 0 {
  2.     healthz.DefaultHealthz()
  3.     go wait.Until(func() {
  4.         err := http.ListenAndServe(net.JoinHostPort(s.HealthzBindAddress, strconv.Itoa(int(s.HealthzPort))), nil)
  5.         if err != nil {
  6.             glog.Errorf("Starting health server failed: %v", err)
  7.         }
  8.     }, 5*time.Second, wait.NeverStop)
  9. }

3.3. RunKubelet

通过各种赋值构造了完整的kubeDeps结构体，最后再执行RunKubelet转入后续的kubelet执行流程。

  1. if err := RunKubelet(s, kubeDeps, s.RunOnce); err != nil {
  2.     return err
  3. }

4. RunKubelet

  1. // RunKubelet is responsible for setting up and running a kubelet.  It is used in three different applications:
  2. //   1 Integration tests
  3. //   2 Kubelet binary
  4. //   3 Standalone 'kubernetes' binary
  5. // Eventually, #2 will be replaced with instances of #3
  6. func RunKubelet(kubeServer *options.KubeletServer, kubeDeps *kubelet.Dependencies, runOnce bool) error {
  7.     ...
  8.     k, err := CreateAndInitKubelet(&kubeServer.KubeletConfiguration,
  9.         ...
  10.         kubeServer.NodeStatusMaxImages)
  11.     if err != nil {
  12.         return fmt.Errorf("failed to create kubelet: %v", err)
  13.     }
  15.     // NewMainKubelet should have set up a pod source config if one didn't exist
  16.     // when the builder was run. This is just a precaution.
  17.     if kubeDeps.PodConfig == nil {
  18.         return fmt.Errorf("failed to create kubelet, pod source config was nil")
  19.     }
  20.     podCfg := kubeDeps.PodConfig
  22.     rlimit.RlimitNumFiles(uint64(kubeServer.MaxOpenFiles))
  24.     // process pods and exit.
  25.     if runOnce {
  26.         if _, err := k.RunOnce(podCfg.Updates()); err != nil {
  27.             return fmt.Errorf("runonce failed: %v", err)
  28.         }
  29.         glog.Infof("Started kubelet as runonce")
  30.     } else {
  31.         startKubelet(k, podCfg, &kubeServer.KubeletConfiguration, kubeDeps, kubeServer.EnableServer)
  32.         glog.Infof("Started kubelet")
  33.     }
  34.     return nil
  35. }

RunKubelet函数核心代码为执行了CreateAndInitKubelet和startKubelet两个函数的操作，以下对这两个函数进行分析。

4.1. CreateAndInitKubelet

通过传入kubeDeps调用CreateAndInitKubelet初始化Kubelet。

  1. k, err := CreateAndInitKubelet(&kubeServer.KubeletConfiguration,
  2.     kubeDeps,
  3.     &kubeServer.ContainerRuntimeOptions,
  4.     kubeServer.ContainerRuntime,
  5.     kubeServer.RuntimeCgroups,
  6.     kubeServer.HostnameOverride,
  7.     kubeServer.NodeIP,
  8.     kubeServer.ProviderID,
  9.     kubeServer.CloudProvider,
  10.     kubeServer.CertDirectory,
  11.     kubeServer.RootDirectory,
  12.     kubeServer.RegisterNode,
  13.     kubeServer.RegisterWithTaints,
  14.     kubeServer.AllowedUnsafeSysctls,
  15.     kubeServer.RemoteRuntimeEndpoint,
  16.     kubeServer.RemoteImageEndpoint,
  17.     kubeServer.ExperimentalMounterPath,
  18.     kubeServer.ExperimentalKernelMemcgNotification,
  19.     kubeServer.ExperimentalCheckNodeCapabilitiesBeforeMount,
  20.     kubeServer.ExperimentalNodeAllocatableIgnoreEvictionThreshold,
  21.     kubeServer.MinimumGCAge,
  22.     kubeServer.MaxPerPodContainerCount,
  23.     kubeServer.MaxContainerCount,
  24.     kubeServer.MasterServiceNamespace,
  25.     kubeServer.RegisterSchedulable,
  26.     kubeServer.NonMasqueradeCIDR,
  27.     kubeServer.KeepTerminatedPodVolumes,
  28.     kubeServer.NodeLabels,
  29.     kubeServer.SeccompProfileRoot,
  30.     kubeServer.BootstrapCheckpointPath,
  31.     kubeServer.NodeStatusMaxImages)
  32. if err != nil {
  33.     return fmt.Errorf("failed to create kubelet: %v", err)
  34. }

4.1.1. NewMainKubelet

CreateAndInitKubelet方法中执行的核心函数是NewMainKubelet，NewMainKubelet实例化一个kubelet对象，该部分的具体代码在kubernetes/pkg/kubelet中，具体参考：kubernetes/pkg/kubelet/kubelet.go#L325。

  1. func CreateAndInitKubelet(kubeCfg *kubeletconfiginternal.KubeletConfiguration,
  2.     ...
  3.     nodeStatusMaxImages int32) (k kubelet.Bootstrap, err error) {
  4.     // TODO: block until all sources have delivered at least one update to the channel, or break the sync loop
  5.     // up into "per source" synchronizations
  7.     k, err = kubelet.NewMainKubelet(kubeCfg,
  8.         kubeDeps,
  9.         crOptions,
  10.         containerRuntime,
  11.         runtimeCgroups,
  12.         hostnameOverride,
  13.         nodeIP,
  14.         providerID,
  15.         cloudProvider,
  16.         certDirectory,
  17.         rootDirectory,
  18.         registerNode,
  19.         registerWithTaints,
  20.         allowedUnsafeSysctls,
  21.         remoteRuntimeEndpoint,
  22.         remoteImageEndpoint,
  23.         experimentalMounterPath,
  24.         experimentalKernelMemcgNotification,
  25.         experimentalCheckNodeCapabilitiesBeforeMount,
  26.         experimentalNodeAllocatableIgnoreEvictionThreshold,
  27.         minimumGCAge,
  28.         maxPerPodContainerCount,
  29.         maxContainerCount,
  30.         masterServiceNamespace,
  31.         registerSchedulable,
  32.         nonMasqueradeCIDR,
  33.         keepTerminatedPodVolumes,
  34.         nodeLabels,
  35.         seccompProfileRoot,
  36.         bootstrapCheckpointPath,
  37.         nodeStatusMaxImages)
  38.     if err != nil {
  39.         return nil, err
  40.     }
  42.     k.BirthCry()
  44.     k.StartGarbageCollection()
  46.     return k, nil
  47. }

4.1.2. PodConfig

  1. if kubeDeps.PodConfig == nil {
  2.     var err error
  3.     kubeDeps.PodConfig, err = makePodSourceConfig(kubeCfg, kubeDeps, nodeName, bootstrapCheckpointPath)
  4.     if err != nil {
  5.         return nil, err
  6.     }
  7. }

NewMainKubelet-->PodConfig-->NewPodConfig-->kubetypes.PodUpdate。会生成一个podUpdate的channel来监听pod的变化，该channel会在k.Run(podCfg.Updates())中作为关键入参。

4.2. startKubelet

  1. // process pods and exit.
  2. if runOnce {
  3.     if _, err := k.RunOnce(podCfg.Updates()); err != nil {
  4.         return fmt.Errorf("runonce failed: %v", err)
  5.     }
  6.     glog.Infof("Started kubelet as runonce")
  7. } else {
  8.     startKubelet(k, podCfg, &kubeServer.KubeletConfiguration, kubeDeps, kubeServer.EnableServer)
  9.     glog.Infof("Started kubelet")
  10. }

如果设置了只运行一次的参数，则执行k.RunOnce，否则执行核心函数startKubelet。具体实现如下：

  1. func startKubelet(k kubelet.Bootstrap, podCfg *config.PodConfig, kubeCfg *kubeletconfiginternal.KubeletConfiguration, kubeDeps *kubelet.Dependencies, enableServer bool) {
  2.     // start the kubelet
  3.     go wait.Until(func() {
  4.         k.Run(podCfg.Updates())
  5.     }, 0, wait.NeverStop)
  7.     // start the kubelet server
  8.     if enableServer {
  9.         go k.ListenAndServe(net.ParseIP(kubeCfg.Address), uint(kubeCfg.Port), kubeDeps.TLSOptions, kubeDeps.Auth, kubeCfg.EnableDebuggingHandlers, kubeCfg.EnableContentionProfiling)
  11.     }
  12.     if kubeCfg.ReadOnlyPort > 0 {
  13.         go k.ListenAndServeReadOnly(net.ParseIP(kubeCfg.Address), uint(kubeCfg.ReadOnlyPort))
  14.     }
  15. }

4.2.1. k.Run

  1. // start the kubelet
  2. go wait.Until(func() {
  3.     k.Run(podCfg.Updates())
  4. }, 0, wait.NeverStop)

通过长驻进程的方式运行k.Run，不退出，将kubelet的运行逻辑引入kubernetes/pkg/kubelet/kubelet.go部分，kubernetes/pkg/kubelet部分的运行逻辑待后续文章分析。

5. 总结

  1. kubelet采用Cobra命令行框架和pflag参数解析框架，和apiserver、scheduler、controller-manager形成统一的代码风格。

  2. kubernetes/cmd/kubelet部分主要对运行参数进行定义和解析，初始化和构造相关的依赖组件（主要在kubeDeps结构体中），并没有kubelet运行的详细逻辑，该部分位于kubernetes/pkg/kubelet模块。

  3. cmd部分调用流程如下：Main-->NewKubeletCommand-->Run(kubeletServer, kubeletDeps, stopCh)-->run(s *options.KubeletServer, kubeDeps ..., stopCh ...)--> RunKubelet(s, kubeDeps, s.RunOnce)-->startKubelet-->k.Run(podCfg.Updates())-->pkg/kubelet。

    同时RunKubelet(s, kubeDeps, s.RunOnce)-->CreateAndInitKubelet-->kubelet.NewMainKubelet-->pkg/kubelet。

参考文章：