apiVersion: v1 
kind: Pod 
metadata: 
  name: nginx-pod 
spec:    
  containers:    
  - name: nginx     
    image: nginx:1.8 

kubectl create -f nginx_pod.yaml 
pod/nginx-pod created

kubectl get pods  
NAME                     READY   STATUS              RESTARTS   AGE 
nginx-pod                1/1     Running             0          4m22s 

func main() {
 	// 如果不調(diào)用rand.Seed，每次重新運(yùn)行這個(gè)main函數(shù)，rand下的函數(shù)返回值始終一致
	// Seed即隨機(jī)的種子，每次用時(shí)間戳作為種子，就能保證隨機(jī)性
	rand.Seed(time.Now().UnixNano())
        // 創(chuàng)建了kubectl命令的默認(rèn)參數(shù)
	command := cmd.NewDefaultKubectlCommand()
	// TODO: once we switch everything over to Cobra commands, we can go back to calling
	// cliflag.InitFlags() (by removing its pflag.Parse() call). For now, we have to set the
	// normalize func and add the go flag set by hand.
	pflag.CommandLine.SetNormalizeFunc(cliflag.WordSepNormalizeFunc)
	pflag.CommandLine.AddGoFlagSet(goflag.CommandLine)
	// cliflag.InitFlags()
        // 日志的初始化與退出
	logs.InitLogs()
	defer logs.FlushLogs()
        // 運(yùn)行command
	if err := command.Execute(); err != nil {
		os.Exit(1)
	}
}

// k8s的命令行工具采用了 cobra 庫(kù)，具有命令提示等強(qiáng)大功能，比go語(yǔ)言自帶的flag強(qiáng)大很多，可參考 github.com/spf13/cobra
func NewDefaultKubectlCommand() *cobra.Command {
	return NewDefaultKubectlCommandWithArgs(NewDefaultPluginHandler(plugin.ValidPluginFilenamePrefixes), os.Args, os.Stdin, os.Stdout, os.Stderr)
}
func NewDefaultKubectlCommandWithArgs(pluginHandler PluginHandler, args []string, in io.Reader, out, errout io.Writer) *cobra.Command {
  // 初始化NewKubectlCommand，采用標(biāo)準(zhǔn)輸入、輸出、錯(cuò)誤輸出
	cmd := NewKubectlCommand(in, out, errout)
	if pluginHandler == nil {
		return cmd
	}
	if len(args) > 1 {
    // 這里為傳入的參數(shù)，即 create -f nginx_pod.yaml 部分
		cmdPathPieces := args[1:]
		// 調(diào)用cobra的Find去匹配args
		if _, _, err := cmd.Find(cmdPathPieces); err != nil {
			if err := HandlePluginCommand(pluginHandler, cmdPathPieces); err != nil {
				fmt.Fprintf(errout, "%v\n", err)
				os.Exit(1)
			}
		}
	}
	return cmd
}

func NewKubectlCommand(in io.Reader, out, err io.Writer) *cobra.Command {
	warningHandler := rest.NewWarningWriter(err, rest.WarningWriterOptions{Deduplicate: true, Color: term.AllowsColorOutput(err)})
	warningsAsErrors := false
	// 創(chuàng)建主命令 告訴你kubectl該怎么用
	cmds := &cobra.Command{
		Use:   "kubectl",
		Short: i18n.T("kubectl controls the Kubernetes cluster manager"),
		Long: templates.LongDesc(`
      kubectl controls the Kubernetes cluster manager.
      Find more information at:
            https://kubernetes.io/docs/reference/kubectl/overview/`),
		Run: runHelp,
		// 初始化后，在運(yùn)行指令前的鉤子
		PersistentPreRunE: func(*cobra.Command, []string) error {
			rest.SetDefaultWarningHandler(warningHandler)
      // 這里是做pprof性能分析，跳轉(zhuǎn)到對(duì)應(yīng)代碼可以看到，我們可以用參數(shù) --profile xxx 來(lái)采集性能指標(biāo)，默認(rèn)保存在當(dāng)前目錄下的profile.pprof中
			return initProfiling()
		},
    // 運(yùn)行指令后的鉤子
		PersistentPostRunE: func(*cobra.Command, []string) error {
      // 保存pprof性能分析指標(biāo)
			if err := flushProfiling(); err != nil {
				return err
			}
      // 打印warning條數(shù)
			if warningsAsErrors {
				count := warningHandler.WarningCount()
				switch count {
				case 0:
					// no warnings
				case 1:
					return fmt.Errorf("%d warning received", count)
				default:
					return fmt.Errorf("%d warnings received", count)
				}
			}
			return nil
		},
    // bash自動(dòng)補(bǔ)齊功能，可通過(guò) kubectl completion bash 命令查看
    // 具體安裝可參考 https://kubernetes.io/docs/tasks/tools/install-kubectl/#enabling-shell-autocompletion
		BashCompletionFunction: bashCompletionFunc,
	}
  // 實(shí)例化Factory接口，工廠模式
	f := cmdutil.NewFactory(matchVersionKubeConfigFlags)
	// 省略實(shí)例化的過(guò)程代碼
  // kubectl定義了7類命令，結(jié)合Message和各個(gè)子命令的package名來(lái)看
	groups := templates.CommandGroups{
		{
      // 1. 初級(jí)命令，包括 create/expose/run/set   
			Message: "Basic Commands (Beginner):",
			Commands: []*cobra.Command{
				create.NewCmdCreate(f, ioStreams),
				expose.NewCmdExposeService(f, ioStreams),
				run.NewCmdRun(f, ioStreams),
				set.NewCmdSet(f, ioStreams),
			},
		},
		{
      // 2. 中級(jí)命令，包括explain/get/edit/delete
			Message: "Basic Commands (Intermediate):",
			Commands: []*cobra.Command{
				explain.NewCmdExplain("kubectl", f, ioStreams),
				get.NewCmdGet("kubectl", f, ioStreams),
				edit.NewCmdEdit(f, ioStreams),
				delete.NewCmdDelete(f, ioStreams),
			},
		},
		{
      // 3. 部署命令，包括 rollout/scale/autoscale
			Message: "Deploy Commands:",
			Commands: []*cobra.Command{
				rollout.NewCmdRollout(f, ioStreams),
				scale.NewCmdScale(f, ioStreams),
				autoscale.NewCmdAutoscale(f, ioStreams),
			},
		},
		{
      // 4. 集群管理命令，包括 cerfificate/cluster-info/top/cordon/drain/taint
			Message: "Cluster Management Commands:",
			Commands: []*cobra.Command{
				certificates.NewCmdCertificate(f, ioStreams),
				clusterinfo.NewCmdClusterInfo(f, ioStreams),
				top.NewCmdTop(f, ioStreams),
				drain.NewCmdCordon(f, ioStreams),
				drain.NewCmdUncordon(f, ioStreams),
				drain.NewCmdDrain(f, ioStreams),
				taint.NewCmdTaint(f, ioStreams),
			},
		},
		{
      // 5. 故障排查和調(diào)試，包括 describe/logs/attach/exec/port-forward/proxy/cp/auth
			Message: "Troubleshooting and Debugging Commands:",
			Commands: []*cobra.Command{
				describe.NewCmdDescribe("kubectl", f, ioStreams),
				logs.NewCmdLogs(f, ioStreams),
				attach.NewCmdAttach(f, ioStreams),
				cmdexec.NewCmdExec(f, ioStreams),
				portforward.NewCmdPortForward(f, ioStreams),
				proxy.NewCmdProxy(f, ioStreams),
				cp.NewCmdCp(f, ioStreams),
				auth.NewCmdAuth(f, ioStreams),
			},
		},
		{
      // 6. 高級(jí)命令，包括diff/apply/patch/replace/wait/convert/kustomize
			Message: "Advanced Commands:",
			Commands: []*cobra.Command{
				diff.NewCmdDiff(f, ioStreams),
				apply.NewCmdApply("kubectl", f, ioStreams),
				patch.NewCmdPatch(f, ioStreams),
				replace.NewCmdReplace(f, ioStreams),
				wait.NewCmdWait(f, ioStreams),
				convert.NewCmdConvert(f, ioStreams),
				kustomize.NewCmdKustomize(ioStreams),
			},
		},
		{
      // 7. 設(shè)置命令，包括label，annotate，completion
			Message: "Settings Commands:",
			Commands: []*cobra.Command{
				label.NewCmdLabel(f, ioStreams),
				annotate.NewCmdAnnotate("kubectl", f, ioStreams),
				completion.NewCmdCompletion(ioStreams.Out, ""),
			},
		},
	}
	groups.Add(cmds)
	filters := []string{"options"}
	// alpha相關(guān)的子命令
	alpha := cmdpkg.NewCmdAlpha(f, ioStreams)
	if !alpha.HasSubCommands() {
		filters = append(filters, alpha.Name())
	}
	templates.ActsAsRootCommand(cmds, filters, groups...)
  // 代碼補(bǔ)全相關(guān)
	for name, completion := range bashCompletionFlags {
		if cmds.Flag(name) != nil {
			if cmds.Flag(name).Annotations == nil {
				cmds.Flag(name).Annotations = map[string][]string{}
			}
			cmds.Flag(name).Annotations[cobra.BashCompCustom] = append(
				cmds.Flag(name).Annotations[cobra.BashCompCustom],
				completion,
			)
		}
	}
  // 添加其余子命令，包括 alpha/config/plugin/version/api-versions/api-resources/options
	cmds.AddCommand(alpha)
	cmds.AddCommand(cmdconfig.NewCmdConfig(f, clientcmd.NewDefaultPathOptions(), ioStreams))
	cmds.AddCommand(plugin.NewCmdPlugin(f, ioStreams))
	cmds.AddCommand(version.NewCmdVersion(f, ioStreams))
	cmds.AddCommand(apiresources.NewCmdAPIVersions(f, ioStreams))
	cmds.AddCommand(apiresources.NewCmdAPIResources(f, ioStreams))
	cmds.AddCommand(options.NewCmdOptions(ioStreams.Out))
	return cmds
}

func NewCmdCreate(f cmdutil.Factory, ioStreams genericclioptions.IOStreams) *cobra.Command {
  // create子命令的相關(guān)選項(xiàng)
	o := NewCreateOptions(ioStreams)
  // create子命令的相關(guān)說(shuō)明
	cmd := &cobra.Command{
		Use:                   "create -f FILENAME",
		DisableFlagsInUseLine: true,
		Short:                 i18n.T("Create a resource from a file or from stdin."),
		Long:                  createLong,
		Example:               createExample,
    // 驗(yàn)證參數(shù)并運(yùn)行
		Run: func(cmd *cobra.Command, args []string) {
			if cmdutil.IsFilenameSliceEmpty(o.FilenameOptions.Filenames, o.FilenameOptions.Kustomize) {
				ioStreams.ErrOut.Write([]byte("Error: must specify one of -f and -k\n\n"))
				defaultRunFunc := cmdutil.DefaultSubCommandRun(ioStreams.ErrOut)
				defaultRunFunc(cmd, args)
				return
			}
			cmdutil.CheckErr(o.Complete(f, cmd))
			cmdutil.CheckErr(o.ValidateArgs(cmd, args))
      // 核心的運(yùn)行代碼邏輯是在這里的RunCreate
			cmdutil.CheckErr(o.RunCreate(f, cmd))
		},
	}
	o.RecordFlags.AddFlags(cmd)
	usage := "to use to create the resource"
  // 加入文件名選項(xiàng)的flag -f，保存到o.FilenameOptions.Filenames中，對(duì)應(yīng)上面
	cmdutil.AddFilenameOptionFlags(cmd, &o.FilenameOptions, usage)
	cmdutil.AddValidateFlags(cmd)
	cmd.Flags().BoolVar(&o.EditBeforeCreate, "edit", o.EditBeforeCreate, "Edit the API resource before creating")
	cmd.Flags().Bool("windows-line-endings", runtime.GOOS == "windows",
		"Only relevant if --edit=true. Defaults to the line ending native to your platform.")
	cmdutil.AddApplyAnnotationFlags(cmd)
	cmdutil.AddDryRunFlag(cmd)
	cmd.Flags().StringVarP(&o.Selector, "selector", "l", o.Selector, "Selector (label query) to filter on, supports '=', '==', and '!='.(e.g. -l key1=value1,key2=value2)")
	cmd.Flags().StringVar(&o.Raw, "raw", o.Raw, "Raw URI to POST to the server.  Uses the transport specified by the kubeconfig file.")
	cmdutil.AddFieldManagerFlagVar(cmd, &o.fieldManager, "kubectl-create")
	o.PrintFlags.AddFlags(cmd)
	// create的子命令，指定create對(duì)象
	cmd.AddCommand(NewCmdCreateNamespace(f, ioStreams))
	cmd.AddCommand(NewCmdCreateQuota(f, ioStreams))
	cmd.AddCommand(NewCmdCreateSecret(f, ioStreams))
	cmd.AddCommand(NewCmdCreateConfigMap(f, ioStreams))
	cmd.AddCommand(NewCmdCreateServiceAccount(f, ioStreams))
	cmd.AddCommand(NewCmdCreateService(f, ioStreams))
	cmd.AddCommand(NewCmdCreateDeployment(f, ioStreams))
	cmd.AddCommand(NewCmdCreateClusterRole(f, ioStreams))
	cmd.AddCommand(NewCmdCreateClusterRoleBinding(f, ioStreams))
	cmd.AddCommand(NewCmdCreateRole(f, ioStreams))
	cmd.AddCommand(NewCmdCreateRoleBinding(f, ioStreams))
	cmd.AddCommand(NewCmdCreatePodDisruptionBudget(f, ioStreams))
	cmd.AddCommand(NewCmdCreatePriorityClass(f, ioStreams))
	cmd.AddCommand(NewCmdCreateJob(f, ioStreams))
	cmd.AddCommand(NewCmdCreateCronJob(f, ioStreams))
	return cmd
}

func (o *CreateOptions) RunCreate(f cmdutil.Factory, cmd *cobra.Command) error {
	// f為傳入的Factory，主要是封裝了與kube-apiserver交互客戶端
	schema, err := f.Validator(cmdutil.GetFlagBool(cmd, "validate"))
	if err != nil {
		return err
	}
	cmdNamespace, enforceNamespace, err := f.ToRawKubeConfigLoader().Namespace()
	if err != nil {
		return err
	}
  // 實(shí)例化Builder，這塊的邏輯比較復(fù)雜，我們先關(guān)注文件部分 這些大部分是給builder設(shè)置參數(shù)，在Do的時(shí)候執(zhí)行邏輯，返回我們想要的Result
	r := f.NewBuilder().
		Unstructured().
		Schema(schema).
		ContinueOnError().
		NamespaceParam(cmdNamespace).DefaultNamespace().
  	// 讀取文件信息，發(fā)現(xiàn)除了支持簡(jiǎn)單的本地文件，也支持標(biāo)準(zhǔn)輸入和http/https協(xié)議訪問(wèn)的文件，保存為Visitor 
		FilenameParam(enforceNamespace, &o.FilenameOptions).
		LabelSelectorParam(o.Selector).
		Flatten().
		Do()
	err = r.Err()
	if err != nil {
		return err
	}
	count := 0
  // 調(diào)用visit函數(shù)，創(chuàng)建資源
	err = r.Visit(func(info *resource.Info, err error) error {
		// 我們看到的pod創(chuàng)建成功就是在這里打印的 打印結(jié)果 xxxx created 
		return o.PrintObj(info.Object)
	})
	return nil
}