kubelet相关标识解析

kubelet对于标识定义这块的代码读起来有点乱，定义了两个标识集合:

func NewKubeletCommand() *cobra.Command {
  cleanFlagSet := pflag.NewFlagSet(componentKubelet, pflag.ContinueOnError)
  cleanFlagSet.SetNormalizeFunc(cliflag.WordSepNormalizeFunc)
  kubeletFlags := options.NewKubeletFlags()
...
}

cleanFlagSet: 全部标识(--help、--version等全局标识 + kubelet标识)
kubeletFlags: kubelet标识

针对这一设计官方有提到

// keep cleanFlagSet separate, so Cobra doesn't pollute it with the global flags
kubeletFlags.AddFlags(cleanFlagSet)
options.AddKubeletConfigFlags(cleanFlagSet, kubeletConfig)
options.AddGlobalFlags(cleanFlagSet)
cleanFlagSet.BoolP("help", "h", false, fmt.Sprintf("help for %s", cmd.Name()))

所有与标识相关的内容如下:

// NewKubeletCommand creates a *cobra.Command object with default parameters
func NewKubeletCommand() *cobra.Command {
    cleanFlagSet := pflag.NewFlagSet(componentKubelet, pflag.ContinueOnError)
    cleanFlagSet.SetNormalizeFunc(cliflag.WordSepNormalizeFunc)
    kubeletFlags := options.NewKubeletFlags()
    kubeletConfig, err := options.NewKubeletConfiguration()
    // programmer error
    if err != nil {
        klog.Fatal(err)
    }
...
    // keep cleanFlagSet separate, so Cobra doesn't pollute it with the global flags
    kubeletFlags.AddFlags(cleanFlagSet)
    options.AddKubeletConfigFlags(cleanFlagSet, kubeletConfig)
    options.AddGlobalFlags(cleanFlagSet)
    cleanFlagSet.BoolP("help", "h", false, fmt.Sprintf("help for %s", cmd.Name()))
...
    return cmd
}

接下来我们逐步分析，标识初始化流程

1.cleanFlagSet初始化

初始化kubelet指令集时会先初始化一部分标识（这里全局标识集合为cleanFlagSet），并赋予默认值。

cleanFlagSet := pflag.NewFlagSet(componentKubelet, pflag.ContinueOnError)
cleanFlagSet.SetNormalizeFunc(cliflag.WordSepNormalizeFunc)
kubeletFlags := options.NewKubeletFlags()
kubeletConfig, err := options.NewKubeletConfiguration()
// programmer error
if err != nil {
    klog.Fatal(err)
}

其中以下部分定义了一个名为cleanFlagSet标识集合，并具有自动将标识中_转换为-能力

cleanFlagSet := pflag.NewFlagSet(componentKubelet, pflag.ContinueOnError)
cleanFlagSet.SetNormalizeFunc(cliflag.WordSepNormalizeFunc)

kubeletFlags := options.NewKubeletFlags()则初始化了kubelet标识集合并赋予默认值

2.添加cleanFlagSet为全局标识

上文我们分析了，kubelet指令在初始化阶段，初始化了一个全局标识对象cleanFlagSet。

它是如何被设置为全局标识的呢？其实是通过以下代码实现：

// NewKubeletCommand creates a *cobra.Command object with default parameters
func NewKubeletCommand() *cobra.Command {
    // keep cleanFlagSet separate, so Cobra doesn't pollute it with the global flags
...
    options.AddGlobalFlags(cleanFlagSet)
...
    return cmd
}

3.kubeletFlags初始化

上文我们了解到，为了更好的管理标识，kubelet定义了两个标识集合:

cleanFlagSet: 全局标识(配置文件路径、容器运行时、证书路径)
kubeletFlags: kubelet标识（kubelet相关标识，包含cleanFlagSet内的标识）

接下来我们分析下kubelet标识集合的初始化流程:

首先通过调用options.NewKubeletFlags()初始化kubeletFlags对象

func NewKubeletCommand() *cobra.Command {
...
  kubeletFlags := options.NewKubeletFlags()
...
}

kubernetes/cmd/kubelet/app/options/options.go

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,
        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"),
        // prior to the introduction of this flag, there was a hardcoded cap of 50 images
        NodeStatusMaxImages:         50,
        EnableCAdvisorJSONEndpoints: false,
    }
}

这里我们创建了一个存放全局标识的对象,即cleanFlagSet，针对其初始化的默认值我们做下简要分析：

EnableServer: 开启kubelet服务端
ContainerRuntimeOptions: 定义了容器运行时选项

func NewContainerRuntimeOptions() *config.ContainerRuntimeOptions {
    dockerEndpoint := ""
    if runtime.GOOS != "windows" {
        dockerEndpoint = "unix:///var/run/docker.sock"
    }

    return &config.ContainerRuntimeOptions{
        ContainerRuntime:           kubetypes.DockerContainerRuntime,
        RedirectContainerStreaming: false,
        DockerEndpoint:             dockerEndpoint,
        DockershimRootDirectory:    "/var/lib/dockershim",
        PodSandboxImage:            defaultPodSandboxImage,
        ImagePullProgressDeadline:  metav1.Duration{Duration: 1 * time.Minute},
        ExperimentalDockershim:     false,

        //Alpha feature
        CNIBinDir:   "/opt/cni/bin",
        CNIConfDir:  "/etc/cni/net.d",
        CNICacheDir: "/var/lib/cni/cache",
    }
}

&config.ContainerRuntimeOptions会初始化一部分字段，并非所有。

ContainerRuntime: 默认使用docker容器运行时（--container-runtime）
RedirectContainerStreaming: 重定向容器流，默认false（--container-runtime）
- 当为true时: kubelet将返回一个HTTP重定向到apiserver，apiserver将直接访问容器运行时。虽然这样的话性能会有所提升，但安全方面又有了隐患（apiserver与容器运行时间无身份认证）
- 当为false时: kubelet将会代理apiserver与容器运行时间的流数据，虽然性能上有些损耗，但也提供了安全保障。
DockerEndpoint: 定义了docker socket路径(unix:///var/run/docker.sock)用于与docker间通信
DockershimRootDirectory: dockershim根目录，默认为/var/lib/dockershim，用于集成测试（例如: OpenShift）
PodSandboxImage: pod沙箱镜像，默认k8s.gcr.io/pause:3.2
ImagePullProgressDeadline: 镜像拉取超时时间，默认1分钟，超过1分钟如果镜像未拉取成功将取消进行镜像拉取。
ExperimentalDockershim: 是否开启dockershim only模式，默认false
CNIBinDir: CNI二进制目录
CNIConfDir: CNI配置文件目录
CNICacheDir: CNI缓存目录
CertDirectory: 存放TLS证书的目录，默认为/var/lib/kubelet/pki。如果指定了tlsCertFile与tlsPrivateKeyFile，该标识会被忽略。
RootDirectory: 存放kubelet文件 (卷挂载，配置等)的目录，默认/var/lib/kubelet
MasterServiceNamespace: 已移除标识。注入到pod中的kubernetes master服务的命名空间，默认default
MaxContainerCount: 已移除标识。当前节点最大容器数量，默认无限制。
MaxPerPodContainerCount: 已移除标识。每一个容器最多在系统中保存的最大已经停止的实例数量，默认为1
MinimumGCAge: 已移除该标识。
NonMasqueradeCIDR: 已移除该标识。
RegisterSchedulable: 已移除该标识。
ExperimentalKernelMemcgNotification: 默认false。如果启用，kubelet将与内核memcg通知集成，以确定是否越过内存回收阈值，而不是轮询。
RemoteRuntimeEndpoint: 运行时服务端点
unix系统: unix:///var/run/dockershim.sock
windows系统: npipe:////./pipe/dockershim
NodeLabels: 注册节点至集群时，提供的节点标签集合(map[string]string)
VolumePluginDir: 存放第三方卷插件的目录，默认/usr/libexec/kubernetes/kubelet-plugins/volume/exec/
RegisterNode: 启用自动注册apiserver，默认true
SeccompProfileRoot: 存放seccomp配置文件的目录，默认为/var/lib/kubelet/seccomp
NodeStatusMaxImages: 限制了node.status.images中上报的映像数量，这是一个实验性的短期标志，用于帮助实现节点可伸缩性。默认50
EnableCAdvisorJSONEndpoints: 启用一些将在未来版本中删除的cAdvisor端点，默认false

4.kubelet配置项初始化

该阶段初始化kubelet配置对象，用以绑定解析启动标识

kubeletConfig, err := options.NewKubeletConfiguration()

5.标识绑定

我们知道，程序想到使用命令行传入进来的参数时，需要定义一个变量去接收解析，以便后续使用。

如果标识比较多的情况，定义一个结构体来存放变量是个很好的选择。接下来我们分析下kubelet是如何将标识与结构体绑定的

func NewKubeletCommand() *cobra.Command {
...
    // keep cleanFlagSet separate, so Cobra doesn't pollute it with the global flags
    kubeletFlags.AddFlags(cleanFlagSet)
    options.AddKubeletConfigFlags(cleanFlagSet, kubeletConfig)
    options.AddGlobalFlags(cleanFlagSet)
    cleanFlagSet.BoolP("help", "h", false, fmt.Sprintf("help for %s", cmd.Name()))
...
    return cmd

我们先分析下kubeletFlags.AddFlags(cleanFlagSet)调用:

func (f *KubeletFlags) AddFlags(mainfs *pflag.FlagSet) {
    fs := pflag.NewFlagSet("", pflag.ExitOnError)
    defer func() {
        // Unhide deprecated flags. We want deprecated flags to show in Kubelet help.
        // We have some hidden flags, but we might as well unhide these when they are deprecated,
        // as silently deprecating and removing (even hidden) things is unkind to people who use them.
        fs.VisitAll(func(f *pflag.Flag) {
            if len(f.Deprecated) > 0 {
                f.Hidden = false
            }
        })
        mainfs.AddFlagSet(fs)
    }()

    f.ContainerRuntimeOptions.AddFlags(fs)
    f.addOSFlags(fs)

    fs.StringVar(&f.KubeletConfigFile, "config", f.KubeletConfigFile, "The Kubelet will load its initial configuration from this file. The path may be absolute or relative; relative paths start at the Kubelet's current working directory. Omit this flag to use the built-in default configuration values. Command-line flags override configuration from this file.")
    fs.StringVar(&f.KubeConfig, "kubeconfig", f.KubeConfig, "Path to a kubeconfig file, specifying how to connect to the API server. Providing --kubeconfig enables API server mode, omitting --kubeconfig enables standalone mode.")

    fs.StringVar(&f.BootstrapKubeconfig, "bootstrap-kubeconfig", f.BootstrapKubeconfig, "Path to a kubeconfig file that will be used to get client certificate for kubelet. "+
        "If the file specified by --kubeconfig does not exist, the bootstrap kubeconfig is used to request a client certificate from the API server. "+
        "On success, a kubeconfig file referencing the generated client certificate and key is written to the path specified by --kubeconfig. "+
        "The client certificate and key file will be stored in the directory pointed by --cert-dir.")

    fs.BoolVar(&f.ReallyCrashForTesting, "really-crash-for-testing", f.ReallyCrashForTesting, "If true, when panics occur crash. Intended for testing.")
    fs.Float64Var(&f.ChaosChance, "chaos-chance", f.ChaosChance, "If > 0.0, introduce random client errors and latency. Intended for testing.")

    fs.BoolVar(&f.RunOnce, "runonce", f.RunOnce, "If true, exit after spawning pods from static pod files or remote urls. Exclusive with --enable-server")
    fs.BoolVar(&f.EnableServer, "enable-server", f.EnableServer, "Enable the Kubelet's server")

    fs.StringVar(&f.HostnameOverride, "hostname-override", f.HostnameOverride, "If non-empty, will use this string as identification instead of the actual hostname. If --cloud-provider is set, the cloud provider determines the name of the node (consult cloud provider documentation to determine if and how the hostname is used).")

    fs.StringVar(&f.NodeIP, "node-ip", f.NodeIP, "IP address of the node. If set, kubelet will use this IP address for the node. If unset, kubelet will use the node's default IPv4 address, if any, or its default IPv6 address if it has no IPv4 addresses. You can pass `::` to make it prefer the default IPv6 address rather than the default IPv4 address.")

    fs.StringVar(&f.ProviderID, "provider-id", f.ProviderID, "Unique identifier for identifying the node in a machine database, i.e cloudprovider")

    fs.StringVar(&f.CertDirectory, "cert-dir", f.CertDirectory, "The directory where the TLS certs are located. "+
        "If --tls-cert-file and --tls-private-key-file are provided, this flag will be ignored.")

    fs.StringVar(&f.CloudProvider, "cloud-provider", f.CloudProvider, "The provider for cloud services. Specify empty string for running with no cloud provider. If set, the cloud provider determines the name of the node (consult cloud provider documentation to determine if and how the hostname is used).")
    fs.StringVar(&f.CloudConfigFile, "cloud-config", f.CloudConfigFile, "The path to the cloud provider configuration file.  Empty string for no configuration file.")

    fs.StringVar(&f.RootDirectory, "root-dir", f.RootDirectory, "Directory path for managing kubelet files (volume mounts,etc).")

    fs.Var(&f.DynamicConfigDir, "dynamic-config-dir", "The Kubelet will use this directory for checkpointing downloaded configurations and tracking configuration health. The Kubelet will create this directory if it does not already exist. The path may be absolute or relative; relative paths start at the Kubelet's current working directory. Providing this flag enables dynamic Kubelet configuration. The DynamicKubeletConfig feature gate must be enabled to pass this flag; this gate currently defaults to true because the feature is beta.")

    fs.BoolVar(&f.RegisterNode, "register-node", f.RegisterNode, "Register the node with the apiserver. If --kubeconfig is not provided, this flag is irrelevant, as the Kubelet won't have an apiserver to register with.")
    fs.Var(utiltaints.NewTaintsVar(&f.RegisterWithTaints), "register-with-taints", "Register the node with the given list of taints (comma separated \"<key>=<value>:<effect>\"). No-op if register-node is false.")

    // EXPERIMENTAL FLAGS
    fs.StringVar(&f.ExperimentalMounterPath, "experimental-mounter-path", f.ExperimentalMounterPath, "[Experimental] Path of mounter binary. Leave empty to use the default mount.")
    fs.BoolVar(&f.ExperimentalKernelMemcgNotification, "experimental-kernel-memcg-notification", f.ExperimentalKernelMemcgNotification, "If enabled, the kubelet will integrate with the kernel memcg notification to determine if memory eviction thresholds are crossed rather than polling.")
    fs.StringVar(&f.RemoteRuntimeEndpoint, "container-runtime-endpoint", f.RemoteRuntimeEndpoint, "[Experimental] The endpoint of remote runtime service. Currently unix socket endpoint is supported on Linux, while npipe and tcp endpoints are supported on windows.  Examples:'unix:///var/run/dockershim.sock', 'npipe:////./pipe/dockershim'")
    fs.StringVar(&f.RemoteImageEndpoint, "image-service-endpoint", f.RemoteImageEndpoint, "[Experimental] The endpoint of remote image service. If not specified, it will be the same with container-runtime-endpoint by default. Currently unix socket endpoint is supported on Linux, while npipe and tcp endpoints are supported on windows.  Examples:'unix:///var/run/dockershim.sock', 'npipe:////./pipe/dockershim'")
    fs.BoolVar(&f.ExperimentalCheckNodeCapabilitiesBeforeMount, "experimental-check-node-capabilities-before-mount", f.ExperimentalCheckNodeCapabilitiesBeforeMount, "[Experimental] if set true, the kubelet will check the underlying node for required components (binaries, etc.) before performing the mount")
    fs.BoolVar(&f.ExperimentalNodeAllocatableIgnoreEvictionThreshold, "experimental-allocatable-ignore-eviction", f.ExperimentalNodeAllocatableIgnoreEvictionThreshold, "When set to 'true', Hard Eviction Thresholds will be ignored while calculating Node Allocatable. See https://kubernetes.io/docs/tasks/administer-cluster/reserve-compute-resources/ for more details. [default=false]")
    bindableNodeLabels := cliflag.ConfigurationMap(f.NodeLabels)
    fs.Var(&bindableNodeLabels, "node-labels", fmt.Sprintf("<Warning: Alpha feature> Labels to add when registering the node in the cluster.  Labels must be key=value pairs separated by ','. Labels in the 'kubernetes.io' namespace must begin with an allowed prefix (%s) or be in the specifically allowed set (%s)", strings.Join(kubeletapis.KubeletLabelNamespaces(), ", "), strings.Join(kubeletapis.KubeletLabels(), ", ")))
    fs.StringVar(&f.VolumePluginDir, "volume-plugin-dir", f.VolumePluginDir, "The full path of the directory in which to search for additional third party volume plugins")
    fs.StringVar(&f.LockFilePath, "lock-file", f.LockFilePath, "<Warning: Alpha feature> The path to file for kubelet to use as a lock file.")
    fs.BoolVar(&f.ExitOnLockContention, "exit-on-lock-contention", f.ExitOnLockContention, "Whether kubelet should exit upon lock-file contention.")
    fs.StringVar(&f.SeccompProfileRoot, "seccomp-profile-root", f.SeccompProfileRoot, "<Warning: Alpha feature> Directory path for seccomp profiles.")
    fs.StringVar(&f.BootstrapCheckpointPath, "bootstrap-checkpoint-path", f.BootstrapCheckpointPath, "<Warning: Alpha feature> Path to the directory where the checkpoints are stored")
    fs.Int32Var(&f.NodeStatusMaxImages, "node-status-max-images", f.NodeStatusMaxImages, "<Warning: Alpha feature> The maximum number of images to report in Node.Status.Images. If -1 is specified, no cap will be applied.")

    // DEPRECATED FLAGS
    fs.StringVar(&f.BootstrapKubeconfig, "experimental-bootstrap-kubeconfig", f.BootstrapKubeconfig, "")
    fs.MarkDeprecated("experimental-bootstrap-kubeconfig", "Use --bootstrap-kubeconfig")
    fs.DurationVar(&f.MinimumGCAge.Duration, "minimum-container-ttl-duration", f.MinimumGCAge.Duration, "Minimum age for a finished container before it is garbage collected.  Examples: '300ms', '10s' or '2h45m'")
    fs.MarkDeprecated("minimum-container-ttl-duration", "Use --eviction-hard or --eviction-soft instead. Will be removed in a future version.")
    fs.Int32Var(&f.MaxPerPodContainerCount, "maximum-dead-containers-per-container", f.MaxPerPodContainerCount, "Maximum number of old instances to retain per container.  Each container takes up some disk space.")
    fs.MarkDeprecated("maximum-dead-containers-per-container", "Use --eviction-hard or --eviction-soft instead. Will be removed in a future version.")
    fs.Int32Var(&f.MaxContainerCount, "maximum-dead-containers", f.MaxContainerCount, "Maximum number of old instances of containers to retain globally.  Each container takes up some disk space. To disable, set to a negative number.")
    fs.MarkDeprecated("maximum-dead-containers", "Use --eviction-hard or --eviction-soft instead. Will be removed in a future version.")
    fs.StringVar(&f.MasterServiceNamespace, "master-service-namespace", f.MasterServiceNamespace, "The namespace from which the kubernetes master services should be injected into pods")
    fs.MarkDeprecated("master-service-namespace", "This flag will be removed in a future version.")
    fs.BoolVar(&f.RegisterSchedulable, "register-schedulable", f.RegisterSchedulable, "Register the node as schedulable. Won't have any effect if register-node is false.")
    fs.MarkDeprecated("register-schedulable", "will be removed in a future version")
    fs.StringVar(&f.NonMasqueradeCIDR, "non-masquerade-cidr", f.NonMasqueradeCIDR, "Traffic to IPs outside this range will use IP masquerade. Set to '0.0.0.0/0' to never masquerade.")
    fs.MarkDeprecated("non-masquerade-cidr", "will be removed in a future version")
    fs.BoolVar(&f.KeepTerminatedPodVolumes, "keep-terminated-pod-volumes", f.KeepTerminatedPodVolumes, "Keep terminated pod volumes mounted to the node after the pod terminates.  Can be useful for debugging volume related issues.")
    fs.MarkDeprecated("keep-terminated-pod-volumes", "will be removed in a future version")
    fs.BoolVar(&f.EnableCAdvisorJSONEndpoints, "enable-cadvisor-json-endpoints", f.EnableCAdvisorJSONEndpoints, "Enable cAdvisor json /spec and /stats/* endpoints.")
    fs.MarkDeprecated("enable-cadvisor-json-endpoints", "will be removed in a future version")

}

函数大致流程如下:

kubelet标识绑定ContainerRuntimeOptions结构体内字段
kubelet添加系统标识(windows)
kubeletFlags标识赋值给cleanFlagSet

options.AddKubeletConfigFlags(cleanFlagSet, kubeletConfig)调用解析

func NewKubeletCommand() *cobra.Command {
...
    options.AddKubeletConfigFlags(cleanFlagSet, kubeletConfig)
    options.AddGlobalFlags(cleanFlagSet)
...
    return cmd
}

AddKubeletConfigFlags()函数主体内容:

// AddKubeletConfigFlags adds flags for a specific kubeletconfig.KubeletConfiguration to the specified FlagSet
func AddKubeletConfigFlags(mainfs *pflag.FlagSet, c *kubeletconfig.KubeletConfiguration) {
    fs := pflag.NewFlagSet("", pflag.ExitOnError)
    defer func() {
        // All KubeletConfiguration flags are now deprecated, and any new flags that point to
        // KubeletConfiguration fields are deprecated-on-creation. When removing flags at the end
        // of their deprecation period, be careful to check that they have *actually* been deprecated
        // members of the KubeletConfiguration for the entire deprecation period:
        // e.g. if a flag was added after this deprecation function, it may not be at the end
        // of its lifetime yet, even if the rest are.
        deprecated := "This parameter should be set via the config file specified by the Kubelet's --config flag. See https://kubernetes.io/docs/tasks/administer-cluster/kubelet-config-file/ for more information."
        fs.VisitAll(func(f *pflag.Flag) {
            f.Deprecated = deprecated
        })
        mainfs.AddFlagSet(fs)
    }()

    fs.BoolVar(&c.FailSwapOn, "fail-swap-on", c.FailSwapOn, "Makes the Kubelet fail to start if swap is enabled on the node. ")
    fs.StringVar(&c.StaticPodPath, "pod-manifest-path", c.StaticPodPath, "Path to the directory containing static pod files to run, or the path to a single static pod file. Files starting with dots will be ignored.")
    fs.DurationVar(&c.SyncFrequency.Duration, "sync-frequency", c.SyncFrequency.Duration, "Max period between synchronizing running containers and config")
    fs.DurationVar(&c.FileCheckFrequency.Duration, "file-check-frequency", c.FileCheckFrequency.Duration, "Duration between checking config files for new data")
    fs.DurationVar(&c.HTTPCheckFrequency.Duration, "http-check-frequency", c.HTTPCheckFrequency.Duration, "Duration between checking http for new data")
    fs.StringVar(&c.StaticPodURL, "manifest-url", c.StaticPodURL, "URL for accessing additional Pod specifications to run")
    fs.Var(cliflag.NewColonSeparatedMultimapStringString(&c.StaticPodURLHeader), "manifest-url-header", "Comma-separated list of HTTP headers to use when accessing the url provided to --manifest-url. Multiple headers with the same name will be added in the same order provided. This flag can be repeatedly invoked. For example: `--manifest-url-header 'a:hello,b:again,c:world' --manifest-url-header 'b:beautiful'`")
    fs.Var(utilflag.IPVar{Val: &c.Address}, "address", "The IP address for the Kubelet to serve on (set to `0.0.0.0` for all IPv4 interfaces and `::` for all IPv6 interfaces)")
    fs.Int32Var(&c.Port, "port", c.Port, "The port for the Kubelet to serve on.")
    fs.Int32Var(&c.ReadOnlyPort, "read-only-port", c.ReadOnlyPort, "The read-only port for the Kubelet to serve on with no authentication/authorization (set to 0 to disable)")

    // Authentication
    fs.BoolVar(&c.Authentication.Anonymous.Enabled, "anonymous-auth", c.Authentication.Anonymous.Enabled, ""+
        "Enables anonymous requests to the Kubelet server. Requests that are not rejected by another "+
        "authentication method are treated as anonymous requests. Anonymous requests have a username "+
        "of system:anonymous, and a group name of system:unauthenticated.")
    fs.BoolVar(&c.Authentication.Webhook.Enabled, "authentication-token-webhook", c.Authentication.Webhook.Enabled, ""+
        "Use the TokenReview API to determine authentication for bearer tokens.")
    fs.DurationVar(&c.Authentication.Webhook.CacheTTL.Duration, "authentication-token-webhook-cache-ttl", c.Authentication.Webhook.CacheTTL.Duration, ""+
        "The duration to cache responses from the webhook token authenticator.")
    fs.StringVar(&c.Authentication.X509.ClientCAFile, "client-ca-file", c.Authentication.X509.ClientCAFile, ""+
        "If set, any request presenting a client certificate signed by one of the authorities in the client-ca-file "+
        "is authenticated with an identity corresponding to the CommonName of the client certificate.")

    // Authorization
    fs.StringVar((*string)(&c.Authorization.Mode), "authorization-mode", string(c.Authorization.Mode), ""+
        "Authorization mode for Kubelet server. Valid options are AlwaysAllow or Webhook. "+
        "Webhook mode uses the SubjectAccessReview API to determine authorization.")
    fs.DurationVar(&c.Authorization.Webhook.CacheAuthorizedTTL.Duration, "authorization-webhook-cache-authorized-ttl", c.Authorization.Webhook.CacheAuthorizedTTL.Duration, ""+
        "The duration to cache 'authorized' responses from the webhook authorizer.")
    fs.DurationVar(&c.Authorization.Webhook.CacheUnauthorizedTTL.Duration, "authorization-webhook-cache-unauthorized-ttl", c.Authorization.Webhook.CacheUnauthorizedTTL.Duration, ""+
        "The duration to cache 'unauthorized' responses from the webhook authorizer.")

    fs.StringVar(&c.TLSCertFile, "tls-cert-file", c.TLSCertFile, ""+
        "File containing x509 Certificate used for serving HTTPS (with intermediate certs, if any, concatenated after server cert). "+
        "If --tls-cert-file and --tls-private-key-file are not provided, a self-signed certificate and key "+
        "are generated for the public address and saved to the directory passed to --cert-dir.")
    fs.StringVar(&c.TLSPrivateKeyFile, "tls-private-key-file", c.TLSPrivateKeyFile, "File containing x509 private key matching --tls-cert-file.")
    fs.BoolVar(&c.ServerTLSBootstrap, "rotate-server-certificates", c.ServerTLSBootstrap, "Auto-request and rotate the kubelet serving certificates by requesting new certificates from the kube-apiserver when the certificate expiration approaches. Requires the RotateKubeletServerCertificate feature gate to be enabled, and approval of the submitted CertificateSigningRequest objects.")

    tlsCipherPossibleValues := cliflag.TLSCipherPossibleValues()
    fs.StringSliceVar(&c.TLSCipherSuites, "tls-cipher-suites", c.TLSCipherSuites,
        "Comma-separated list of cipher suites for the server. "+
            "If omitted, the default Go cipher suites will be used. "+
            "Possible values: "+strings.Join(tlsCipherPossibleValues, ","))
    tlsPossibleVersions := cliflag.TLSPossibleVersions()
    fs.StringVar(&c.TLSMinVersion, "tls-min-version", c.TLSMinVersion,
        "Minimum TLS version supported. "+
            "Possible values: "+strings.Join(tlsPossibleVersions, ", "))
    fs.BoolVar(&c.RotateCertificates, "rotate-certificates", c.RotateCertificates, "<Warning: Beta feature> Auto rotate the kubelet client certificates by requesting new certificates from the kube-apiserver when the certificate expiration approaches.")

    fs.Int32Var(&c.RegistryPullQPS, "registry-qps", c.RegistryPullQPS, "If > 0, limit registry pull QPS to this value.  If 0, unlimited.")
    fs.Int32Var(&c.RegistryBurst, "registry-burst", c.RegistryBurst, "Maximum size of a bursty pulls, temporarily allows pulls to burst to this number, while still not exceeding registry-qps. Only used if --registry-qps > 0")
    fs.Int32Var(&c.EventRecordQPS, "event-qps", c.EventRecordQPS, "If > 0, limit event creations per second to this value. If 0, unlimited.")
    fs.Int32Var(&c.EventBurst, "event-burst", c.EventBurst, "Maximum size of a bursty event records, temporarily allows event records to burst to this number, while still not exceeding event-qps. Only used if --event-qps > 0")

    fs.BoolVar(&c.EnableDebuggingHandlers, "enable-debugging-handlers", c.EnableDebuggingHandlers, "Enables server endpoints for log collection and local running of containers and commands")
    fs.BoolVar(&c.EnableContentionProfiling, "contention-profiling", c.EnableContentionProfiling, "Enable lock contention profiling, if profiling is enabled")
    fs.Int32Var(&c.HealthzPort, "healthz-port", c.HealthzPort, "The port of the localhost healthz endpoint (set to 0 to disable)")
    fs.Var(utilflag.IPVar{Val: &c.HealthzBindAddress}, "healthz-bind-address", "The IP address for the healthz server to serve on (set to `0.0.0.0` for all IPv4 interfaces and `::` for all IPv6 interfaces)")
    fs.Int32Var(&c.OOMScoreAdj, "oom-score-adj", c.OOMScoreAdj, "The oom-score-adj value for kubelet process. Values must be within the range [-1000, 1000]")
    fs.StringVar(&c.ClusterDomain, "cluster-domain", c.ClusterDomain, "Domain for this cluster.  If set, kubelet will configure all containers to search this domain in addition to the host's search domains")

    fs.StringSliceVar(&c.ClusterDNS, "cluster-dns", c.ClusterDNS, "Comma-separated list of DNS server IP address.  This value is used for containers DNS server in case of Pods with \"dnsPolicy=ClusterFirst\". Note: all DNS servers appearing in the list MUST serve the same set of records otherwise name resolution within the cluster may not work correctly. There is no guarantee as to which DNS server may be contacted for name resolution.")
    fs.DurationVar(&c.StreamingConnectionIdleTimeout.Duration, "streaming-connection-idle-timeout", c.StreamingConnectionIdleTimeout.Duration, "Maximum time a streaming connection can be idle before the connection is automatically closed. 0 indicates no timeout. Example: '5m'")
    fs.DurationVar(&c.NodeStatusUpdateFrequency.Duration, "node-status-update-frequency", c.NodeStatusUpdateFrequency.Duration, "Specifies how often kubelet posts node status to master. Note: be cautious when changing the constant, it must work with nodeMonitorGracePeriod in nodecontroller.")
    fs.DurationVar(&c.ImageMinimumGCAge.Duration, "minimum-image-ttl-duration", c.ImageMinimumGCAge.Duration, "Minimum age for an unused image before it is garbage collected.  Examples: '300ms', '10s' or '2h45m'.")
    fs.Int32Var(&c.ImageGCHighThresholdPercent, "image-gc-high-threshold", c.ImageGCHighThresholdPercent, "The percent of disk usage after which image garbage collection is always run. Values must be within the range [0, 100], To disable image garbage collection, set to 100. ")
    fs.Int32Var(&c.ImageGCLowThresholdPercent, "image-gc-low-threshold", c.ImageGCLowThresholdPercent, "The percent of disk usage before which image garbage collection is never run. Lowest disk usage to garbage collect to. Values must be within the range [0, 100] and should not be larger than that of --image-gc-high-threshold.")
    fs.DurationVar(&c.VolumeStatsAggPeriod.Duration, "volume-stats-agg-period", c.VolumeStatsAggPeriod.Duration, "Specifies interval for kubelet to calculate and cache the volume disk usage for all pods and volumes.  To disable volume calculations, set to 0.")
    fs.Var(cliflag.NewMapStringBool(&c.FeatureGates), "feature-gates", "A set of key=value pairs that describe feature gates for alpha/experimental features. "+
        "Options are:\n"+strings.Join(utilfeature.DefaultFeatureGate.KnownFeatures(), "\n"))
    fs.StringVar(&c.KubeletCgroups, "kubelet-cgroups", c.KubeletCgroups, "Optional absolute name of cgroups to create and run the Kubelet in.")
    fs.StringVar(&c.SystemCgroups, "system-cgroups", c.SystemCgroups, "Optional absolute name of cgroups in which to place all non-kernel processes that are not already inside a cgroup under `/`. Empty for no container. Rolling back the flag requires a reboot.")

    fs.BoolVar(&c.CgroupsPerQOS, "cgroups-per-qos", c.CgroupsPerQOS, "Enable creation of QoS cgroup hierarchy, if true top level QoS and pod cgroups are created.")
    fs.StringVar(&c.CgroupDriver, "cgroup-driver", c.CgroupDriver, "Driver that the kubelet uses to manipulate cgroups on the host.  Possible values: 'cgroupfs', 'systemd'")
    fs.StringVar(&c.CgroupRoot, "cgroup-root", c.CgroupRoot, "Optional root cgroup to use for pods. This is handled by the container runtime on a best effort basis. Default: '', which means use the container runtime default.")
    fs.StringVar(&c.CPUManagerPolicy, "cpu-manager-policy", c.CPUManagerPolicy, "CPU Manager policy to use. Possible values: 'none', 'static'. Default: 'none'")
    fs.DurationVar(&c.CPUManagerReconcilePeriod.Duration, "cpu-manager-reconcile-period", c.CPUManagerReconcilePeriod.Duration, "<Warning: Alpha feature> CPU Manager reconciliation period. Examples: '10s', or '1m'. If not supplied, defaults to `NodeStatusUpdateFrequency`")
    fs.Var(cliflag.NewMapStringString(&c.QOSReserved), "qos-reserved", "<Warning: Alpha feature> A set of ResourceName=Percentage (e.g. memory=50%) pairs that describe how pod resource requests are reserved at the QoS level. Currently only memory is supported. Requires the QOSReserved feature gate to be enabled.")
    fs.StringVar(&c.TopologyManagerPolicy, "topology-manager-policy", c.TopologyManagerPolicy, "Topology Manager policy to use. Possible values: 'none', 'best-effort', 'restricted', 'single-numa-node'.")
    fs.DurationVar(&c.RuntimeRequestTimeout.Duration, "runtime-request-timeout", c.RuntimeRequestTimeout.Duration, "Timeout of all runtime requests except long running request - pull, logs, exec and attach. When timeout exceeded, kubelet will cancel the request, throw out an error and retry later.")
    fs.StringVar(&c.HairpinMode, "hairpin-mode", c.HairpinMode, "How should the kubelet setup hairpin NAT. This allows endpoints of a Service to loadbalance back to themselves if they should try to access their own Service. Valid values are \"promiscuous-bridge\", \"hairpin-veth\" and \"none\".")
    fs.Int32Var(&c.MaxPods, "max-pods", c.MaxPods, "Number of Pods that can run on this Kubelet.")

    fs.StringVar(&c.PodCIDR, "pod-cidr", c.PodCIDR, "The CIDR to use for pod IP addresses, only used in standalone mode.  In cluster mode, this is obtained from the master. For IPv6, the maximum number of IP's allocated is 65536")
    fs.Int64Var(&c.PodPidsLimit, "pod-max-pids", c.PodPidsLimit, "Set the maximum number of processes per pod.  If -1, the kubelet defaults to the node allocatable pid capacity.")

    fs.StringVar(&c.ResolverConfig, "resolv-conf", c.ResolverConfig, "Resolver configuration file used as the basis for the container DNS resolution configuration.")
    fs.BoolVar(&c.CPUCFSQuota, "cpu-cfs-quota", c.CPUCFSQuota, "Enable CPU CFS quota enforcement for containers that specify CPU limits")
    fs.DurationVar(&c.CPUCFSQuotaPeriod.Duration, "cpu-cfs-quota-period", c.CPUCFSQuotaPeriod.Duration, "Sets CPU CFS quota period value, cpu.cfs_period_us, defaults to Linux Kernel default")
    fs.BoolVar(&c.EnableControllerAttachDetach, "enable-controller-attach-detach", c.EnableControllerAttachDetach, "Enables the Attach/Detach controller to manage attachment/detachment of volumes scheduled to this node, and disables kubelet from executing any attach/detach operations")
    fs.BoolVar(&c.MakeIPTablesUtilChains, "make-iptables-util-chains", c.MakeIPTablesUtilChains, "If true, kubelet will ensure iptables utility rules are present on host.")
    fs.Int32Var(&c.IPTablesMasqueradeBit, "iptables-masquerade-bit", c.IPTablesMasqueradeBit, "The bit of the fwmark space to mark packets for SNAT. Must be within the range [0, 31]. Please match this parameter with corresponding parameter in kube-proxy.")
    fs.Int32Var(&c.IPTablesDropBit, "iptables-drop-bit", c.IPTablesDropBit, "The bit of the fwmark space to mark packets for dropping. Must be within the range [0, 31].")
    fs.StringVar(&c.ContainerLogMaxSize, "container-log-max-size", c.ContainerLogMaxSize, "<Warning: Beta feature> Set the maximum size (e.g. 10Mi) of container log file before it is rotated. This flag can only be used with --container-runtime=remote.")
    fs.Int32Var(&c.ContainerLogMaxFiles, "container-log-max-files", c.ContainerLogMaxFiles, "<Warning: Beta feature> Set the maximum number of container log files that can be present for a container. The number must be >= 2. This flag can only be used with --container-runtime=remote.")
    fs.StringSliceVar(&c.AllowedUnsafeSysctls, "allowed-unsafe-sysctls", c.AllowedUnsafeSysctls, "Comma-separated whitelist of unsafe sysctls or unsafe sysctl patterns (ending in *). Use these at your own risk.")

    // Flags intended for testing, not recommended used in production environments.
    fs.Int64Var(&c.MaxOpenFiles, "max-open-files", c.MaxOpenFiles, "Number of files that can be opened by Kubelet process.")

    fs.StringVar(&c.ContentType, "kube-api-content-type", c.ContentType, "Content type of requests sent to apiserver.")
    fs.Int32Var(&c.KubeAPIQPS, "kube-api-qps", c.KubeAPIQPS, "QPS to use while talking with kubernetes apiserver")
    fs.Int32Var(&c.KubeAPIBurst, "kube-api-burst", c.KubeAPIBurst, "Burst to use while talking with kubernetes apiserver")
    fs.BoolVar(&c.SerializeImagePulls, "serialize-image-pulls", c.SerializeImagePulls, "Pull images one at a time. We recommend *not* changing the default value on nodes that run docker daemon with version < 1.9 or an Aufs storage backend. Issue #10959 has more details.")

    fs.Var(cliflag.NewLangleSeparatedMapStringString(&c.EvictionHard), "eviction-hard", "A set of eviction thresholds (e.g. memory.available<1Gi) that if met would trigger a pod eviction.")
    fs.Var(cliflag.NewLangleSeparatedMapStringString(&c.EvictionSoft), "eviction-soft", "A set of eviction thresholds (e.g. memory.available<1.5Gi) that if met over a corresponding grace period would trigger a pod eviction.")
    fs.Var(cliflag.NewMapStringString(&c.EvictionSoftGracePeriod), "eviction-soft-grace-period", "A set of eviction grace periods (e.g. memory.available=1m30s) that correspond to how long a soft eviction threshold must hold before triggering a pod eviction.")
    fs.DurationVar(&c.EvictionPressureTransitionPeriod.Duration, "eviction-pressure-transition-period", c.EvictionPressureTransitionPeriod.Duration, "Duration for which the kubelet has to wait before transitioning out of an eviction pressure condition.")
    fs.Int32Var(&c.EvictionMaxPodGracePeriod, "eviction-max-pod-grace-period", c.EvictionMaxPodGracePeriod, "Maximum allowed grace period (in seconds) to use when terminating pods in response to a soft eviction threshold being met.  If negative, defer to pod specified value.")
    fs.Var(cliflag.NewMapStringString(&c.EvictionMinimumReclaim), "eviction-minimum-reclaim", "A set of minimum reclaims (e.g. imagefs.available=2Gi) that describes the minimum amount of resource the kubelet will reclaim when performing a pod eviction if that resource is under pressure.")
    fs.Int32Var(&c.PodsPerCore, "pods-per-core", c.PodsPerCore, "Number of Pods per core that can run on this Kubelet. The total number of Pods on this Kubelet cannot exceed max-pods, so max-pods will be used if this calculation results in a larger number of Pods allowed on the Kubelet. A value of 0 disables this limit.")
    fs.BoolVar(&c.ProtectKernelDefaults, "protect-kernel-defaults", c.ProtectKernelDefaults, "Default kubelet behaviour for kernel tuning. If set, kubelet errors if any of kernel tunables is different than kubelet defaults.")
    fs.StringVar(&c.ReservedSystemCPUs, "reserved-cpus", c.ReservedSystemCPUs, "A comma-separated list of CPUs or CPU ranges that are reserved for system and kubernetes usage. This specific list will supersede cpu counts in --system-reserved and --kube-reserved.")
    // Node Allocatable Flags
    fs.Var(cliflag.NewMapStringString(&c.SystemReserved), "system-reserved", "A set of ResourceName=ResourceQuantity (e.g. cpu=200m,memory=500Mi,ephemeral-storage=1Gi) pairs that describe resources reserved for non-kubernetes components. Currently only cpu and memory are supported. See http://kubernetes.io/docs/user-guide/compute-resources for more detail. [default=none]")
    fs.Var(cliflag.NewMapStringString(&c.KubeReserved), "kube-reserved", "A set of ResourceName=ResourceQuantity (e.g. cpu=200m,memory=500Mi,ephemeral-storage=1Gi) pairs that describe resources reserved for kubernetes system components. Currently cpu, memory and local ephemeral storage for root file system are supported. See http://kubernetes.io/docs/user-guide/compute-resources for more detail. [default=none]")
    fs.StringSliceVar(&c.EnforceNodeAllocatable, "enforce-node-allocatable", c.EnforceNodeAllocatable, "A comma separated list of levels of node allocatable enforcement to be enforced by kubelet. Acceptable options are 'none', 'pods', 'system-reserved', and 'kube-reserved'. If the latter two options are specified, '--system-reserved-cgroup' and '--kube-reserved-cgroup' must also be set, respectively. If 'none' is specified, no additional options should be set. See https://kubernetes.io/docs/tasks/administer-cluster/reserve-compute-resources/ for more details.")
    fs.StringVar(&c.SystemReservedCgroup, "system-reserved-cgroup", c.SystemReservedCgroup, "Absolute name of the top level cgroup that is used to manage non-kubernetes components for which compute resources were reserved via '--system-reserved' flag. Ex. '/system-reserved'. [default='']")
    fs.StringVar(&c.KubeReservedCgroup, "kube-reserved-cgroup", c.KubeReservedCgroup, "Absolute name of the top level cgroup that is used to manage kubernetes components for which compute resources were reserved via '--kube-reserved' flag. Ex. '/kube-reserved'. [default='']")
}

该调用做了两件事情：

将kubeletconfig.KubeletConfiguration结构体字段与标识绑定
为cleanFlagSet添加kubelet配置项相关的标识（如：--max-open-files对应kubeletconfig.KubeletConfiguration结构体中MaxOpenFiles字段）

最终通过以下调用，为cleanFlagSet添加--help等标识

func NewKubeletCommand() *cobra.Command {
...
    options.AddGlobalFlags(cleanFlagSet)
    cleanFlagSet.BoolP("help", "h", false, fmt.Sprintf("help for %s", cmd.Name()))

    // ugly, but necessary, because Cobra's default UsageFunc and HelpFunc pollute the flagset with global flags
    const usageFmt = "Usage:\n  %s\n\nFlags:\n%s"
    cmd.SetUsageFunc(func(cmd *cobra.Command) error {
        fmt.Fprintf(cmd.OutOrStderr(), usageFmt, cmd.UseLine(), cleanFlagSet.FlagUsagesWrapped(2))
        return nil
    })
    cmd.SetHelpFunc(func(cmd *cobra.Command, args []string) {
        fmt.Fprintf(cmd.OutOrStdout(), "%s\n\n"+usageFmt, cmd.Long, cmd.UseLine(), cleanFlagSet.FlagUsagesWrapped(2))
    })

    return cmd
}

03标识初始化