kubectl 源码之create namespace_--create-namespace-优快云博客

func NewCmdCreateNamespace(f cmdutil.Factory, ioStreams genericclioptions.IOStreams) *cobra.Command {
	options := &NamespaceOpts{
		CreateSubcommandOptions: NewCreateSubcommandOptions(ioStreams),
	}

	cmd := &cobra.Command{
		Use:                   "namespace NAME [--dry-run]",
		DisableFlagsInUseLine: true,
		Aliases:               []string{"ns"},
		Short:                 i18n.T("Create a namespace with the specified name"),
		Long:                  namespaceLong,
		Example:               namespaceExample,
		Run: func(cmd *cobra.Command, args []string) {
			cmdutil.CheckErr(options.Complete(f, cmd, args))
			cmdutil.CheckErr(options.Run())
		},
	}

	options.CreateSubcommandOptions.PrintFlags.AddFlags(cmd)

	cmdutil.AddApplyAnnotationFlags(cmd)
	cmdutil.AddValidateFlags(cmd)
	cmdutil.AddGeneratorFlags(cmd, generateversioned.NamespaceV1GeneratorName)

	return cmd
}

创建create ns 命令，option有save-config,validate,generator,output

type NamespaceOpts struct {
	CreateSubcommandOptions *CreateSubcommandOptions
}

create选项，内嵌一个CreateSubcommandOptions选项

func (o *NamespaceOpts) Complete(f cmdutil.Factory, cmd *cobra.Command, args []string) error {
	name, err := NameFromCommandArgs(cmd, args)
	if err != nil {
		return err
	}

	var generator generate.StructuredGenerator
	switch generatorName := cmdutil.GetFlagString(cmd, "generator"); generatorName {
	case generateversioned.NamespaceV1GeneratorName:
		generator = &generateversioned.NamespaceGeneratorV1{Name: name}
	default:
		return errUnsupportedGenerator(cmd, generatorName)
	}

	return o.CreateSubcommandOptions.Complete(f, cmd, args, generator)
}

namespceoption complete方法，抽取namespace name，判断generator，然后运行createSubCommandOption的complete

func (o *CreateSubcommandOptions) Complete(f cmdutil.Factory, cmd *cobra.Command, args []string, generator generate.StructuredGenerator) error {
	name, err := NameFromCommandArgs(cmd, args)
	if err != nil {
		return err
	}

	o.Name = name
	o.StructuredGenerator = generator
	o.DryRun = cmdutil.GetDryRunFlag(cmd)
	o.CreateAnnotation = cmdutil.GetFlagBool(cmd, cmdutil.ApplyAnnotationsFlag)

	if o.DryRun {
		o.PrintFlags.Complete("%s (dry run)")
	}
	printer, err := o.PrintFlags.ToPrinter()
	if err != nil {
		return err
	}

	o.PrintObj = func(obj kruntime.Object, out io.Writer) error {
		return printer.PrintObj(obj, out)
	}

	o.Namespace, o.EnforceNamespace, err = f.ToRawKubeConfigLoader().Namespace()
	if err != nil {
		return err
	}

	o.DynamicClient, err = f.DynamicClient()
	if err != nil {
		return err
	}

	o.Mapper, err = f.ToRESTMapper()
	if err != nil {
		return err
	}

	return nil
}

create子命令completion方法，获取namespace name，设置namespacename，设置generator，设置save-config flag，判断dry-run，printflag转换为printer，设置printObj方法，获取namespace和enforcenamespace，设置dynamicClient，设置mapper。

RESTClient：RESTClient是最基础的，相当于的底层基础结构，可以直接通过是RESTClient提供的RESTful方法如Get()，Put()，Post()，Delete()进行交互
- 同时支持Json 和 protobuf
- 支持所有原生资源和CRDs
- 但是，一般而言，为了更为优雅的处理，需要进一步封装，通过Clientset封装RESTClient，然后再对外提供接口和服务

Clientset：Clientset是调用Kubernetes资源对象最常用的client，可以操作所有的资源对象，包含RESTClient。需要指定Group、指定Version，然后根据Resource获取
- 优雅的姿势是利用一个controller对象，再加上Informer
DynamicClient：Dynamic client 是一种动态的 client，它能处理 kubernetes 所有的资源。不同于 clientset，dynamic client 返回的对象是一个 map[string]interface{}，如果一个 controller 中需要控制所有的 API，可以使用dynamic client，目前它在 garbage collector 和 namespace controller中被使用。

func (o *NamespaceOpts) Run() error {
	return o.CreateSubcommandOptions.Run()
}

实际运行逻辑，是CreatesubCommandOption的run

func (o *CreateSubcommandOptions) Run() error {
	obj, err := o.StructuredGenerator.StructuredGenerate()
	if err != nil {
		return err
	}
	if !o.DryRun {
		// create subcommands have compiled knowledge of things they create, so type them directly
		gvks, _, err := scheme.Scheme.ObjectKinds(obj)
		if err != nil {
			return err
		}
		gvk := gvks[0]
		mapping, err := o.Mapper.RESTMapping(schema.GroupKind{Group: gvk.Group, Kind: gvk.Kind}, gvk.Version)
		if err != nil {
			return err
		}

		if err := util.CreateOrUpdateAnnotation(o.CreateAnnotation, obj, scheme.DefaultJSONEncoder()); err != nil {
			return err
		}

		asUnstructured := &unstructured.Unstructured{}

		if err := scheme.Scheme.Convert(obj, asUnstructured, nil); err != nil {
			return err
		}
		if mapping.Scope.Name() == meta.RESTScopeNameRoot {
			o.Namespace = ""
		}
		actualObject, err := o.DynamicClient.Resource(mapping.Resource).Namespace(o.Namespace).Create(asUnstructured, metav1.CreateOptions{})
		if err != nil {
			return err
		}

		// ensure we pass a versioned object to the printer
		obj = actualObject
	} else {
		if meta, err := meta.Accessor(obj); err == nil && o.EnforceNamespace {
			meta.SetNamespace(o.Namespace)
		}
	}

	return o.PrintObj(obj, o.Out)
}

根据generator后去obj对象，如果是非干跑，获取groupversionkind，获取restmapping，根据save-config选项更新注解

把obj转换为Unstructured，根据mapping的scope设置namespace，用DynamicClient创建资源。打印obj。