Kubernetes源码学习-Kubelet-P1-启动流程

矫情吗；* 2023-01-18 09:29 54阅读 0赞

## 前言 ##

在大致分析过k8s的Scheduler、Controller、APIServer三个控制平面组件后，本篇开始进入数据交互平面的daemon组件kubelet部分，看看kubelet是如何在控制平面和数据平面中以承上启下的模式工作的。

## 启动流程 ##

启动入口照旧，位于项目的cmd路径下，使用cobra做cmd封装：

`cmd/kubelet/kubelet.go:39`

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

`cmd/kubelet/app/server.go:112`

`NewKubeletFlags`和`NewKubeletConfiguration`方法会初始化kubelet的很多默认flag和参数，来分别看下：

`cmd/kubelet/app/options/options.go:214`

func NewKubeletFlags() *KubeletFlags { 
    	remoteRuntimeEndpoint := ""
    	if runtime.GOOS == "linux" { 
    		remoteRuntimeEndpoint = "unix:///var/run/dockershim.sock"
    	} else if runtime.GOOS == "windows" { 
    		remoteRuntimeEndpoint = "npipe:./pipe/dockershim"
    	}
    
    	return &KubeletFlags{ 
    		EnableServer:                        true,
        // 容器运行时这个参数需要留意下
    		ContainerRuntimeOptions:             *NewContainerRuntimeOptions(),
    		CertDirectory:                       "/var/lib/kubelet/pki",
    		RootDirectory:                       defaultRootDir,
    		MasterServiceNamespace:              metav1.NamespaceDefault,
    		MaxContainerCount:                   -1,
    		MaxPerPodContainerCount:             1,
    		MinimumGCAge:                        metav1.Duration{ Duration: 0},
    		NonMasqueradeCIDR:                   "10.0.0.0/8",
    		RegisterSchedulable:                 true,
    		ExperimentalKernelMemcgNotification: false,
    		RemoteRuntimeEndpoint:               remoteRuntimeEndpoint,
    		NodeLabels:                          make(map[string]string),
    		VolumePluginDir:                     "/usr/libexec/kubernetes/kubelet-plugins/volume/exec/",
    		RegisterNode:                        true,
    		SeccompProfileRoot:                  filepath.Join(defaultRootDir, "seccomp"),
    		HostNetworkSources:                  []string{ kubetypes.AllSource},
    		HostPIDSources:                      []string{ kubetypes.AllSource},
    		HostIPCSources:                      []string{ kubetypes.AllSource},
    		// TODO(#58010:v1.13.0): Remove --allow-privileged, it is deprecated
    		AllowPrivileged: true,
    		// prior to the introduction of this flag, there was a hardcoded cap of 50 images
    		NodeStatusMaxImages: 50,
    	}
    }

ContainerRuntimeOptions有必要看看：

`cmd/kubelet/app/options/container_runtime.go:41`

func NewContainerRuntimeOptions() *config.ContainerRuntimeOptions { 
    	dockerEndpoint := ""
    	if runtime.GOOS != "windows" { 
        // 默认的容器驱动是docker
    		dockerEndpoint = "unix:///var/run/docker.sock"
    	}
    
    	return &config.ContainerRuntimeOptions{ 
    		ContainerRuntime:           kubetypes.DockerContainerRuntime,
    		RedirectContainerStreaming: false,
    		DockerEndpoint:             dockerEndpoint,
        // dockershim路径，dockershim是容器运行中的实际载体，每个docker容器都会产生一个shim进程
    		DockershimRootDirectory:    "/var/lib/dockershim",
        // pause容器
    		PodSandboxImage:            defaultPodSandboxImage,
    		ImagePullProgressDeadline:  metav1.Duration{ Duration: 1 * time.Minute},
    		ExperimentalDockershim:     false,
    
    		// 这个目录下都是网络相关功能工具的执行文件
    		CNIBinDir:  "/opt/cni/bin",
        // 这里是cni的配置文件，如pod网段、网关、bridge等，一般由cni动态生成
    		CNIConfDir: "/etc/cni/net.d",
    	}
    }

`cmd/kubelet/app/options/options.go:293`

–> `cmd/kubelet/app/options/options.go:311`

// `NewKubeletConfiguration`方法则会默认设置一些参数
    func applyLegacyDefaults(kc *kubeletconfig.KubeletConfiguration) { 
    	// --anonymous-auth
    	kc.Authentication.Anonymous.Enabled = true
    	// --authentication-token-webhook
    	kc.Authentication.Webhook.Enabled = false
    	// --authorization-mode
      // apiserver认证篇提到的针对node设计的AlwaysAllow认证模式
    	kc.Authorization.Mode = kubeletconfig.KubeletAuthorizationModeAlwaysAllow
    	// 10255采集信息的接口，如prometheus采集cadvisor的metrics
    	kc.ReadOnlyPort = ports.KubeletReadOnlyPort
    }

再来看看Run方法里面做了哪些操作:

–> `cmd/kubelet/app/server.go:148`

Run: func(cmd *cobra.Command, args []string) { 
          ...
    			// 上面百来行代码都是默认的init flag和config相关处理，例如featureGates等，略过
          
          // 加载kubelet配置文件，展开进去看可以看到即是--config参数对应指定的文件，一般kubeadm部署时使用的是/var/lib/kubelet/config.yaml
    			if configFile := kubeletFlags.KubeletConfigFile; len(configFile) > 0 { 
    				kubeletConfig, err = loadConfigFile(configFile)
    				if err != nil { 
    					klog.Fatal(err)
    				}
          ... 
    			}
          
    			// 实例化KubeletServer
    			kubeletServer := &options.KubeletServer{ 
    				KubeletFlags:         *kubeletFlags,
    				KubeletConfiguration: *kubeletConfig,
    			}
    
    			// 构建一些kubelet的依赖插件，例如nsenter，连接dockershim的client端
    			kubeletDeps, err := UnsecuredDependencies(kubeletServer)
    			if err != nil { 
    				klog.Fatal(err)
    			}
    
    			// add the kubelet config controller to kubeletDeps
    			kubeletDeps.KubeletConfigController = kubeletConfigController
    
    			// start the experimental docker shim, if enabled
    			if kubeletServer.KubeletFlags.ExperimentalDockershim { 
    				if err := RunDockershim(&kubeletServer.KubeletFlags, kubeletConfig, stopCh); err != nil { 
    					klog.Fatal(err)
    				}
    				return
    			}
    
    			// 启动kubelet
    			klog.V(5).Infof("KubeletConfiguration: %#v", kubeletServer.KubeletConfiguration)
    			if err := Run(kubeletServer, kubeletDeps, stopCh); err != nil { 
    				klog.Fatal(err)
    			}
    		},
    	}
    
    	// 下面是一些cmd help信息，省略
      ...
    
    	return cmd

–> `cmd/kubelet/app/server.go:416`

–> `cmd/kubelet/app/server.go:479` 这个函数代码段很长，两百多行，挑主要片段

func run(s *options.KubeletServer, kubeDeps *kubelet.Dependencies, stopCh <-chan struct{ }) (err error) { 
     ...
    
      // 独立模式指的是不与外部(如apiserver)交互的模式，一般在调试中使用，所以独立模式不需要起client
    	standaloneMode := true
    	if len(s.KubeConfig) > 0 { 
    		standaloneMode = false
    	}
    
    	if kubeDeps == nil { 
    		kubeDeps, err = UnsecuredDependencies(s)
    		if err != nil { 
    			return err
    		}
    	}
    
      // 取得注册node名
    	hostName, err := nodeutil.GetHostname(s.HostnameOverride)
    	if err != nil { 
    		return err
    	}
    	nodeName, err := getNodeName(kubeDeps.Cloud, hostName)
    	if err != nil { 
    		return err
    	}
    
    	
    	switch { 
        // 独立模式，则所有client设为nil
    	case standaloneMode:
    		kubeDeps.KubeClient = nil
    		kubeDeps.EventClient = nil
    		kubeDeps.HeartbeatClient = nil
    		klog.Warningf("standalone mode, no API client")
    	
       // 正常模式，则初始化client，包括kubeClient/eventClient/heartBeatClient
    	case kubeDeps.KubeClient == nil, kubeDeps.EventClient == nil, kubeDeps.HeartbeatClient == nil:
        // client的配置，主要是连接apiserver的cert相关的配置，cert文件默认放在/var/lib/kubelet/pki下，如果开启了循环续期证书，则相应的异步进程会从cert manager循环检测和更新证书。其他的配置诸如超时时间，长连接时间等。closeAllConns接收的是一个方法，用来断开连接。
    		clientConfig, closeAllConns, err := buildKubeletClientConfig(s, nodeName)
    		if err != nil { 
    			return err
    		}
    		if closeAllConns == nil { 
    			return errors.New("closeAllConns must be a valid function other than nil")
    		}
    		kubeDeps.OnHeartbeatFailure = closeAllConns
    		// 构建一个client-go里的clientset实例，访问各个GV和GVR对象使用
    		kubeDeps.KubeClient, err = clientset.NewForConfig(clientConfig)
    		if err != nil { 
    			return fmt.Errorf("failed to initialize kubelet client: %v", err)
    		}
    
    		// event事件使用独立的client，与上面的访问GVR使用的client区分开
    		eventClientConfig := *clientConfig
    		eventClientConfig.QPS = float32(s.EventRecordQPS)
    		eventClientConfig.Burst = int(s.EventBurst)
    		kubeDeps.EventClient, err = v1core.NewForConfig(&eventClientConfig)
    		if err != nil { 
    			return fmt.Errorf("failed to initialize kubelet event client: %v", err)
    		}
    
    		// 再开启一个心跳检测的client
    		heartbeatClientConfig := *clientConfig
    		heartbeatClientConfig.Timeout = s.KubeletConfiguration.NodeStatusUpdateFrequency.Duration
        // 如果开启了NodeLease(node定期向apiserver汇报运行状态)，那么心跳间隔最大不超过NodeLease duration
    		if utilfeature.DefaultFeatureGate.Enabled(features.NodeLease) { 
    			leaseTimeout := time.Duration(s.KubeletConfiguration.NodeLeaseDurationSeconds) * time.Second
    			if heartbeatClientConfig.Timeout > leaseTimeout { 
    				heartbeatClientConfig.Timeout = leaseTimeout
    			}
    		}
        // 心跳1次/s
    		heartbeatClientConfig.QPS = float32(-1)
    		kubeDeps.HeartbeatClient, err = clientset.NewForConfig(&heartbeatClientConfig)
    		if err != nil { 
    			return fmt.Errorf("failed to initialize kubelet heartbeat client: %v", err)
    		}
    	}
      // 向apiserver发起认证建立会话
    	if kubeDeps.Auth == nil { 
    		auth, err := BuildAuth(nodeName, kubeDeps.KubeClient, s.KubeletConfiguration)
    		if err != nil { 
    			return err
    		}
    		kubeDeps.Auth = auth
    	}
      // 填充cadvisor接口
    	if kubeDeps.CAdvisorInterface == nil { 
    		imageFsInfoProvider := cadvisor.NewImageFsInfoProvider(s.ContainerRuntime, s.RemoteRuntimeEndpoint)
    		kubeDeps.CAdvisorInterface, err = cadvisor.New(imageFsInfoProvider, s.RootDirectory, cadvisor.UsingLegacyCadvisorStats(s.ContainerRuntime, s.RemoteRuntimeEndpoint))
    		if err != nil { 
    			return err
    		}
    	}
    
    	// Setup event recorder if required.
    	makeEventRecorder(kubeDeps, nodeName)
    
    	if kubeDeps.ContainerManager == nil { 
    		if s.CgroupsPerQOS && s.CgroupRoot == "" { 
    			klog.Info("--cgroups-per-qos enabled, but --cgroup-root was not specified. defaulting to /")
    			s.CgroupRoot = "/"
    		}
        // /var/lib/kubelt/config.yaml里可以指定，为系统和kube组件指定不同的cgroup，为它们预留资源
        // kubeReserved即为kube组件指定cgroup预留的资源
    		kubeReserved, err := parseResourceList(s.KubeReserved)
    		if err != nil { 
    			return err
    		}
        // kubeReserved即为宿主机系统进程指定cgroup预留的资源
    		systemReserved, err := parseResourceList(s.SystemReserved)
    		if err != nil { 
    			return err
    		}
        // 硬驱逐容器的资源阈值
    		var hardEvictionThresholds []evictionapi.Threshold
    		// If the user requested to ignore eviction thresholds, then do not set valid values for hardEvictionThresholds here.
    		if !s.ExperimentalNodeAllocatableIgnoreEvictionThreshold { 
    			hardEvictionThresholds, err = eviction.ParseThresholdConfig([]string{ }, s.EvictionHard, nil, nil, nil)
    			if err != nil { 
    				return err
    			}
    		}
    		experimentalQOSReserved, err := cm.ParseQOSReserved(s.QOSReserved)
    		if err != nil { 
    			return err
    		}
    
    		devicePluginEnabled := utilfeature.DefaultFeatureGate.Enabled(features.DevicePlugins)
        
        // 上面的参数汇集起来，初始化容器管理器
    		kubeDeps.ContainerManager, err = cm.NewContainerManager(
    			kubeDeps.Mounter,
    			kubeDeps.CAdvisorInterface,
    			cm.NodeConfig{ 
    				RuntimeCgroupsName:    s.RuntimeCgroups,
    				SystemCgroupsName:     s.SystemCgroups,
    				KubeletCgroupsName:    s.KubeletCgroups,
    				ContainerRuntime:      s.ContainerRuntime,
    				CgroupsPerQOS:         s.CgroupsPerQOS,
    				CgroupRoot:            s.CgroupRoot,
    				CgroupDriver:          s.CgroupDriver,
    				KubeletRootDir:        s.RootDirectory,
    				ProtectKernelDefaults: s.ProtectKernelDefaults,
    				NodeAllocatableConfig: cm.NodeAllocatableConfig{ 
    					KubeReservedCgroupName:   s.KubeReservedCgroup,
    					SystemReservedCgroupName: s.SystemReservedCgroup,
    					EnforceNodeAllocatable:   sets.NewString(s.EnforceNodeAllocatable...),
    					KubeReserved:             kubeReserved,
    					SystemReserved:           systemReserved,
    					HardEvictionThresholds:   hardEvictionThresholds,
    				},
    				QOSReserved:                           *experimentalQOSReserved,
    				ExperimentalCPUManagerPolicy:          s.CPUManagerPolicy,
    				ExperimentalCPUManagerReconcilePeriod: s.CPUManagerReconcilePeriod.Duration,
    				ExperimentalPodPidsLimit:              s.PodPidsLimit,
    				EnforceCPULimits:                      s.CPUCFSQuota,
    				CPUCFSQuotaPeriod:                     s.CPUCFSQuotaPeriod.Duration,
    			},
    			s.FailSwapOn,
    			devicePluginEnabled,
    			kubeDeps.Recorder)
    
    		if err != nil { 
    			return err
    		}
    	}
       
    	if err := checkPermissions(); err != nil { 
    		klog.Error(err)
    	}
    
    	utilruntime.ReallyCrash = s.ReallyCrashForTesting
    
    	rand.Seed(time.Now().UnixNano())
    
    	// oom判定器给当前进程设置oom分数，容器内存资源管控的手段就是使用的oom，这里待会儿拎出来单独分析
    	oomAdjuster := kubeDeps.OOMAdjuster
    	if err := oomAdjuster.ApplyOOMScoreAdj(0, int(s.OOMScoreAdj)); err != nil { 
    		klog.Warning(err)
    	}
      // RunKubelet接往下文
    	if err := RunKubelet(s, kubeDeps, s.RunOnce); err != nil { 
    		return err
    	}
      // 起一个健康检查的http服务
    	if s.HealthzPort > 0 { 
    		healthz.DefaultHealthz()
    		go wait.Until(func() { 
    			err := http.ListenAndServe(net.JoinHostPort(s.HealthzBindAddress, strconv.Itoa(int(s.HealthzPort))), nil)
    			if err != nil { 
    				klog.Errorf("Starting health server failed: %v", err)
    			}
    		}, 5*time.Second, wait.NeverStop)
    	}
    
    	if s.RunOnce { 
    		return nil
    	}
    
    	// If systemd is used, notify it that we have started
    	go daemon.SdNotify(false, "READY=1")
    
    	select { 
    	case <-done:
    		break
    	case <-stopCh:
    		break
    	}
    
    	return nil
    }

### OOMAdjuster ###

–> `pkg/util/oom/oom.go:22`上面提到的oom判定器，这里分析一下，这个结构体有三个方法:

// 这里目前用的还是结构体，看todo描述是后面要改成interface
    // TODO: make this an interface, and inject a mock ioutil struct for testing.
    type OOMAdjuster struct { 
    	pidLister                 func(cgroupName string) ([]int, error)
    	ApplyOOMScoreAdj          func(pid int, oomScoreAdj int) error
    	ApplyOOMScoreAdjContainer func(cgroupName string, oomScoreAdj, maxTries int) error
    }

–> `pkg/util/oom/oom_linux.go:35`实现方法

func NewOOMAdjuster() *OOMAdjuster { 
    	oomAdjuster := &OOMAdjuster{ 
    		pidLister:        getPids,
    		ApplyOOMScoreAdj: applyOOMScoreAdj,
    	}
    	oomAdjuster.ApplyOOMScoreAdjContainer = oomAdjuster.applyOOMScoreAdjContainer
    	return oomAdjuster
    }
    // 获取cgroup下所有进程的pid
    func getPids(cgroupName string) ([]int, error) { 
    	return cmutil.GetPids(filepath.Join("/", cgroupName))
    }
    
    // 修改oom分数，在linux下即是修改/proc/<pid>/oom_score_adj对应的值，当内存紧张时由linux系统的oom机制去杀掉oom score最高的进程，默认情况下是使用内存越多的进程oom score越高越容易被kill，applyOOMScoreAdj函数就是用来修改oom score的。
    
    // Writes 'value' to /proc/<pid>/oom_score_adj. PID = 0 means self
    // Returns os.ErrNotExist if the `pid` does not exist.
    func applyOOMScoreAdj(pid int, oomScoreAdj int) error { 
    	if pid < 0 { 
    		return fmt.Errorf("invalid PID %d specified for oom_score_adj", pid)
    	}
    
    	var pidStr string
    	if pid == 0 { 
    		pidStr = "self"
    	} else { 
    		pidStr = strconv.Itoa(pid)
    	}
    
    	maxTries := 2
    	oomScoreAdjPath := path.Join("/proc", pidStr, "oom_score_adj")
    	value := strconv.Itoa(oomScoreAdj)
    	klog.V(4).Infof("attempting to set %q to %q", oomScoreAdjPath, value)
    	var err error
    	for i := 0; i < maxTries; i++ { 
    		err = ioutil.WriteFile(oomScoreAdjPath, []byte(value), 0700)
    		if err != nil { 
    			if os.IsNotExist(err) { 
    				klog.V(2).Infof("%q does not exist", oomScoreAdjPath)
    				return os.ErrNotExist
    			}
    
    			klog.V(3).Info(err)
    			time.Sleep(100 * time.Millisecond)
    			continue
    		}
    		return nil
    	}
    	if err != nil { 
    		klog.V(2).Infof("failed to set %q to %q: %v", oomScoreAdjPath, value, err)
    	}
    	return err
    }
    
    // 修改整个容器的oom评分，即修改某个cgroup下所有进程的评分，getPids取得所有pid遍历执行applyOOMScoreAdj
    // Writes 'value' to /proc/<pid>/oom_score_adj for all processes in cgroup cgroupName.
    // Keeps trying to write until the process list of the cgroup stabilizes, or until maxTries tries.
    func (oomAdjuster *OOMAdjuster) applyOOMScoreAdjContainer(cgroupName string, oomScoreAdj, maxTries int) error { 
    	adjustedProcessSet := make(map[int]bool)
    	for i := 0; i < maxTries; i++ { 
    		continueAdjusting := false
    		pidList, err := oomAdjuster.pidLister(cgroupName)
    		if err != nil { 
    			if os.IsNotExist(err) { 
    				// Nothing to do since the container doesn't exist anymore.
    				return os.ErrNotExist
    			}
    			continueAdjusting = true
    			klog.V(10).Infof("Error getting process list for cgroup %s: %+v", cgroupName, err)
    		} else if len(pidList) == 0 { 
    			klog.V(10).Infof("Pid list is empty")
    			continueAdjusting = true
    		} else { 
    			for _, pid := range pidList { 
    				if !adjustedProcessSet[pid] { 
    					klog.V(10).Infof("pid %d needs to be set", pid)
    					if err = oomAdjuster.ApplyOOMScoreAdj(pid, oomScoreAdj); err == nil { 
    						adjustedProcessSet[pid] = true
    					} else if err == os.ErrNotExist { 
    						continue
    					} else { 
    						klog.V(10).Infof("cannot adjust oom score for pid %d - %v", pid, err)
    						continueAdjusting = true
    					}
    					// Processes can come and go while we try to apply oom score adjust value. So ignore errors here.
    				}
    			}
    		}
    		if !continueAdjusting { 
    			return nil
    		}
    		// There's a slight race. A process might have forked just before we write its OOM score adjust.
    		// The fork might copy the parent process's old OOM score, then this function might execute and
    		// update the parent's OOM score, but the forked process id might not be reflected in cgroup.procs
    		// for a short amount of time. So this function might return without changing the forked process's
    		// OOM score. Very unlikely race, so ignoring this for now.
    	}
    	return fmt.Errorf("exceeded maxTries, some processes might not have desired OOM score")
    }

### RunKubelet ###

–> `cmd/kubelet/app/server.go:955` 回到主线

func RunKubelet(kubeServer *options.KubeletServer, kubeDeps *kubelet.Dependencies, runOnce bool) error { 
    	...
      
      // 这里的几个source都是"*"，意为接收api/file/http来源的pod更新
    	hostNetworkSources, err := kubetypes.GetValidatedSources(kubeServer.HostNetworkSources)
    	if err != nil { 
    		return err
    	}
    
    	hostPIDSources, err := kubetypes.GetValidatedSources(kubeServer.HostPIDSources)
    	if err != nil { 
    		return err
    	}
    
    	hostIPCSources, err := kubetypes.GetValidatedSources(kubeServer.HostIPCSources)
    	if err != nil { 
    		return err
    	}
    
    	privilegedSources := capabilities.PrivilegedSources{ 
    		HostNetworkSources: hostNetworkSources,
    		HostPIDSources:     hostPIDSources,
    		HostIPCSources:     hostIPCSources,
    	}
    	capabilities.Setup(kubeServer.AllowPrivileged, privilegedSources, 0)
    
    	credentialprovider.SetPreferredDockercfgPath(kubeServer.RootDirectory)
    	klog.V(2).Infof("Using root directory: %v", kubeServer.RootDirectory)
    
    	if kubeDeps.OSInterface == nil { 
    		kubeDeps.OSInterface = kubecontainer.RealOS{ }
    	}
      
      // kubelet初始化，这个函数比较复杂，下面拎出来分析
    	k, err := createAndInitKubelet(&kubeServer.KubeletConfiguration,
    		kubeDeps,
    		&kubeServer.ContainerRuntimeOptions,
    		kubeServer.ContainerRuntime,
    		kubeServer.RuntimeCgroups,
    		kubeServer.HostnameOverride,
    		kubeServer.NodeIP,
    		kubeServer.ProviderID,
    		kubeServer.CloudProvider,
    		kubeServer.CertDirectory,
    		kubeServer.RootDirectory,
    		kubeServer.RegisterNode,
    		kubeServer.RegisterWithTaints,
    		kubeServer.AllowedUnsafeSysctls,
    		kubeServer.RemoteRuntimeEndpoint,
    		kubeServer.RemoteImageEndpoint,
    		kubeServer.ExperimentalMounterPath,
    		kubeServer.ExperimentalKernelMemcgNotification,
    		kubeServer.ExperimentalCheckNodeCapabilitiesBeforeMount,
    		kubeServer.ExperimentalNodeAllocatableIgnoreEvictionThreshold,
    		kubeServer.MinimumGCAge,
    		kubeServer.MaxPerPodContainerCount,
    		kubeServer.MaxContainerCount,
    		kubeServer.MasterServiceNamespace,
    		kubeServer.RegisterSchedulable,
    		kubeServer.NonMasqueradeCIDR,
    		kubeServer.KeepTerminatedPodVolumes,
    		kubeServer.NodeLabels,
    		kubeServer.SeccompProfileRoot,
    		kubeServer.BootstrapCheckpointPath,
    		kubeServer.NodeStatusMaxImages)
    	if err != nil { 
    		return fmt.Errorf("failed to create kubelet: %v", err)
    	}
    
    	// NewMainKubelet should have set up a pod source config if one didn't exist
    	// when the builder was run. This is just a precaution.
    	if kubeDeps.PodConfig == nil { 
    		return fmt.Errorf("failed to create kubelet, pod source config was nil")
    	}
    	podCfg := kubeDeps.PodConfig
    
    	rlimit.RlimitNumFiles(uint64(kubeServer.MaxOpenFiles))
    
    	// 只运行一次处理完pod就退出
    	if runOnce { 
    		if _, err := k.RunOnce(podCfg.Updates()); err != nil { 
    			return fmt.Errorf("runonce failed: %v", err)
    		}
    		klog.Info("Started kubelet as runonce")
    	} else { 
        // 正常运行
    		startKubelet(k, podCfg, &kubeServer.KubeletConfiguration, kubeDeps, kubeServer.EnableServer)
    		klog.Info("Started kubelet")
    	}
    	return nil
    }

### createAndInitKubelet ###

–> `cmd/kubelet/app/server.go:1078`，这里主要走到NewMainKubelet函数:

–> `pkg/kubelet/kubelet.go:326` God！这个函数简直了，500+行代码…挑重要的说一下吧

func NewMainKubelet(...) (...) { 
      ...
      // 加载service informer
      serviceIndexer := cache.NewIndexer(cache.MetaNamespaceKeyFunc, cache.Indexers{ cache.NamespaceIndex: cache.MetaNamespaceIndexFunc})
    	if kubeDeps.KubeClient != nil { 
    		serviceLW := cache.NewListWatchFromClient(kubeDeps.KubeClient.CoreV1().RESTClient(), "services", metav1.NamespaceAll, fields.Everything())
    		r := cache.NewReflector(serviceLW, &v1.Service{ }, serviceIndexer, 0)
    		go r.Run(wait.NeverStop)
    	}
    	serviceLister := corelisters.NewServiceLister(serviceIndexer)
      
      // 加载node informer
    	nodeIndexer := cache.NewIndexer(cache.MetaNamespaceKeyFunc, cache.Indexers{ })
    	if kubeDeps.KubeClient != nil { 
    		fieldSelector := fields.Set{ api.ObjectNameField: string(nodeName)}.AsSelector()
    		nodeLW := cache.NewListWatchFromClient(kubeDeps.KubeClient.CoreV1().RESTClient(), "nodes", metav1.NamespaceAll, fieldSelector)
    		r := cache.NewReflector(nodeLW, &v1.Node{ }, nodeIndexer, 0)
    		go r.Run(wait.NeverStop)
    	}
    	nodeInfo := &predicates.CachedNodeInfo{ NodeLister: corelisters.NewNodeLister(nodeIndexer)}
    
      ...
      
      // secretManager和configMapManager初始化，因为这两者被使用都是需要往容器内挂载目录的，需要kubelet来参与
      var secretManager secret.Manager
    	var configMapManager configmap.Manager
    	switch kubeCfg.ConfigMapAndSecretChangeDetectionStrategy { 
    	case kubeletconfiginternal.WatchChangeDetectionStrategy:
    		secretManager = secret.NewWatchingSecretManager(kubeDeps.KubeClient)
    		configMapManager = configmap.NewWatchingConfigMapManager(kubeDeps.KubeClient)
    	case kubeletconfiginternal.TTLCacheChangeDetectionStrategy:
    		secretManager = secret.NewCachingSecretManager(
    			kubeDeps.KubeClient, manager.GetObjectTTLFromNodeFunc(klet.GetNode))
    		configMapManager = configmap.NewCachingConfigMapManager(
    			kubeDeps.KubeClient, manager.GetObjectTTLFromNodeFunc(klet.GetNode))
    	case kubeletconfiginternal.GetChangeDetectionStrategy:
    		secretManager = secret.NewSimpleSecretManager(kubeDeps.KubeClient)
    		configMapManager = configmap.NewSimpleConfigMapManager(kubeDeps.KubeClient)
    	default:
    		return nil, fmt.Errorf("unknown configmap and secret manager mode: %v", kubeCfg.ConfigMapAndSecretChangeDetectionStrategy)
    	}
    
    	klet.secretManager = secretManager
    	klet.configMapManager = configMapManager
    
      // 初始化存活探针管理器
      klet.livenessManager = proberesults.NewManager()
      
      //专为dockershim开辟的网络插件集 
    	pluginSettings := dockershim.NetworkPluginSettings{ 
    		HairpinMode:        kubeletconfiginternal.HairpinMode(kubeCfg.HairpinMode),
    		NonMasqueradeCIDR:  nonMasqueradeCIDR,
    		PluginName:         crOptions.NetworkPluginName,
    		PluginConfDir:      crOptions.CNIConfDir,  // 默认在/etc/cni/net.d/下存放cni配置文件
    		PluginBinDirString: crOptions.CNIBinDir,   // 默认在/opt/cni/bin/下存放cni二进制文件，如bridge/tuning/vlan/dhcp/macvlan等等
    		MTU:                int(crOptions.NetworkPluginMTU), // 网卡mtu
    	}  
      
      // kubelet相关运行时初始化 
    	runtime, err := kuberuntime.NewKubeGenericRuntimeManager(
    		kubecontainer.FilterEventRecorder(kubeDeps.Recorder),
    		klet.livenessManager,
    		seccompProfileRoot,
    		containerRefManager,
    		machineInfo,
    		klet,
    		kubeDeps.OSInterface,
    		klet,
    		httpClient,
    		imageBackOff,
    		kubeCfg.SerializeImagePulls,
    		float32(kubeCfg.RegistryPullQPS),
    		int(kubeCfg.RegistryBurst),
    		kubeCfg.CPUCFSQuota,
    		kubeCfg.CPUCFSQuotaPeriod,
    		runtimeService,
    		imageService,
    		kubeDeps.ContainerManager.InternalContainerLifecycle(),
    		legacyLogProvider,
    		klet.runtimeClassManager,
    	)
    	if err != nil { 
    		return nil, err
    	}
    	klet.containerRuntime = runtime
    	klet.streamingRuntime = runtime
    	klet.runner = runtime
    
    	runtimeCache, err := kubecontainer.NewRuntimeCache(klet.containerRuntime)
    	if err != nil { 
    		return nil, err
    	}
    	klet.runtimeCache = runtimeCache  
      
      // pleg初始化(Pod Lifecycle Event Generator)
      klet.pleg = pleg.NewGenericPLEG(klet.containerRuntime, plegChannelCapacity,      plegRelistPeriod, klet.podCache, clock.RealClock{ })
      
      // pod workQueue初始化
      klet.workQueue = queue.NewBasicWorkQueue(klet.clock)
      // pod worker初始化，worker从workQueue中取队首，根据指令对pod进行相应的直接操作，另外还有更新pod cache的操作
    	klet.podWorkers = newPodWorkers(klet.syncPod, kubeDeps.Recorder, klet.workQueue, klet.resyncInterval, backOffPeriod, klet.podCache)
    
    	klet.backOff = flowcontrol.NewBackOff(backOffPeriod, MaxContainerBackOff)
    	klet.podKillingCh = make(chan *kubecontainer.PodPair, podKillingChannelCapacity)
    
    	// 初始化驱逐管理器
    	evictionManager, evictionAdmitHandler := eviction.NewManager(klet.resourceAnalyzer, evictionConfig, killPodNow(klet.podWorkers, kubeDeps.Recorder), klet.podManager.GetMirrorPodByPod, klet.imageManager, klet.containerGC, kubeDeps.Recorder, nodeRef, klet.clock)
    
    	klet.evictionManager = evictionManager
    	klet.admitHandlers.AddPodAdmitHandler(evictionAdmitHandler)
      
      ...
    }

再次回到主线，进入最后的k.Run()函数循环逻辑：

–> `cmd/kubelet/app/server.go:1058`

func startKubelet(k kubelet.Bootstrap, podCfg *config.PodConfig, kubeCfg *kubeletconfiginternal.KubeletConfiguration, kubeDeps *kubelet.Dependencies, enableServer bool) { 
    	// start the kubelet
      // 循环执行kubelet的工作逻辑k.Run()方法
    	go wait.Until(func() { 
    		k.Run(podCfg.Updates())
    	}, 0, wait.NeverStop)
    
    	// start the kubelet server
      // 提供诸如/metrics /health等api
    	if enableServer { 
    		go k.ListenAndServe(net.ParseIP(kubeCfg.Address), uint(kubeCfg.Port), kubeDeps.TLSOptions, kubeDeps.Auth, kubeCfg.EnableDebuggingHandlers, kubeCfg.EnableContentionProfiling)
    
    	}
      // 配置查询api
    	if kubeCfg.ReadOnlyPort > 0 { 
    		go k.ListenAndServeReadOnly(net.ParseIP(kubeCfg.Address), uint(kubeCfg.ReadOnlyPort))
    	}
    	if utilfeature.DefaultFeatureGate.Enabled(features.KubeletPodResources) { 
    		go k.ListenAndServePodResources()
    	}
    }

wait.Until()循环执行函数前面的文章中已经分析过多次了，不再赘述，来分析一下k.Run(podCfg.Updates())传的实参是什么:

–> `pkg/kubelet/config/config.go:105`

func (c *PodConfig) Updates() <-chan kubetypes.PodUpdate {
       return c.updates
    }

接着看`c.updates` \--> `pkg/kubelet/config/config.go:58`

type PodConfig struct { 
       pods *podStorage
       mux  *config.Mux
    
       // the channel of denormalized changes passed to listeners
       updates chan kubetypes.PodUpdate
    
       // contains the list of all configured sources
       sourcesLock       sync.Mutex
       sources           sets.String
       checkpointManager checkpointmanager.CheckpointManager
    }

–> `pkg/kubelet/types/pod_update.go:80`

type PodUpdate struct { 
       Pods   []*v1.Pod
       Op     PodOperation
       Source string
    }

猜测是将pod的写(删查改)请求转换成结构体，放入chan中，然后由k.Run()方法来处理这些写请求，k.Run()的实现在这里\`\`pkg/kubelet/kubelet.go:1382\`，留作下回分析，本篇启动流程篇到此结束。

## 小结 ##

kubelet的源码果真是相当的复杂，一个函数动辄数百行，也难怪，毕竟作为daemon端执行数据平面工作的它要承担着很多职责，先到这吧