Kubernetes1.5源码分析(三) apiServer之go-restful的使用

源码版本

Kubernetes v1.5.0

go-restful

简介

go-restful是用于构建REST-style web服务的golang包。
它是出现时因为一个javaer在golang中没找到顺手的REST-based服务构建包，所以就按照他在java里常用的JAX-RS的设计，在golang中造了一个轮子。

关键组件

1.Route:
路由包含两种，一种是标准JSR311接口规范的实现RouterJSR311,一种是快速路由CurlyRouter。
CurlyRouter支持正则表达式和动态参数，相比RouterJSR11更加轻量级，apiserver中使用的就是这种路由。
一种Route的设定包含：请求方法(http Method)，请求路径(URL Path),输入输出类型(JSON/YAML)以及对应的回掉函数restful.RouteFunction，响应内容类型(Accept)等。

2.WebService：
WebService逻辑上是Route的集合，功能上主要是为一组Route统一设置包括root path,请求响应的数据类型等一些通用的属性。
需要注意的是，WebService必须加入到Container中才能生效。

func (g *APIGroupVersion) InstallREST(container *restful.Container) error {
    installer := g.newInstaller()
    ws := installer.NewWebService()
    。。。
    container.Add(ws)
    return utilerrors.NewAggregate(registrationErrors)
}

上面是k8s的REST注册接口，也调用了Container.Add(ws)，才能让这个ws生效。

3.Container：
Container逻辑上是WebService的集合，功能上可以实现多终端的效果。
它包括一组restful.WebService和一个http.ServeMux对象，使用RouteSelector进行请求派发。
例如，下面代码中创建了两个Container，分别在不同的port上提供服务。
该代码是go-restful的example：

package main

import (
    "github.com/emicklei/go-restful"
    "io"
    "log"
    "net/http"
)

func main() {
    ws := new(restful.WebService)
    ws.Route(ws.GET("/hello").To(hello))
    // ws被添加到默认的container restful.DefaultContainer中
    restful.Add(ws)
    go func() {
        // restful.DefaultContainer监听在端口8080上
        http.ListenAndServe(":8080", nil)
    }()

    container2 := restful.NewContainer()
    ws2 := new(restful.WebService)
    ws2.Route(ws2.GET("/hello").To(hello2))
    // ws2被添加到container2中
    container2.Add(ws2)
    // container2中监听端口8081
    server := &http.Server{Addr: ":8081", Handler: container2}
    log.Fatal(server.ListenAndServe())
}

func hello(req *restful.Request, resp *restful.Response) {
    io.WriteString(resp, "default world")
}

func hello2(req *restful.Request, resp *restful.Response) {
    io.WriteString(resp, "second world")
}

4.Filter:
Filter用于动态的拦截请求和响应，类似于放置在相应组件前的钩子，在相应组件功能运行前捕获请求或者响应，主要用于记录log，验证，重定向等功能。
go-restful中有三种类型的Filter：

• Container Filter:
  运行在Container中所有的WebService执行之前。

  // install a (global) filter for the default container (processed before any webservice)
  restful.Filter(globalLogging)

• WebService Filter：
  运行在WebService中所有的Route执行之前。

  // install a webservice filter (processed before any route)
  ws.Filter(webserviceLogging).Filter(measureTime)

• Route Filter:
  运行在调用Route绑定的方法之前。

  // install 2 chained route filters (processed before calling findUser)
  ws.Route(ws.GET("/{user-id}").Filter(routeLogging).Filter(NewCountFilter().routeCounter).To(findUser))

示例

拿用官方提供的例子：

package main

import (
    "github.com/emicklei/go-restful"
    "log"
    "net/http"
)

type User struct {
    Id, Name string
}

type UserResource struct {
    // normally one would use DAO (data access object)
    users map[string]User
}

func (u UserResource) Register(container *restful.Container) {
      // 创建新的WebService
    ws := new(restful.WebService)
  
      // 设定WebService对应的路径("/users")和支持的MIME类型(restful.MIME_XML/ restful.MIME_JSON)
    ws.
        Path("/users").
        Consumes(restful.MIME_XML, restful.MIME_JSON).
        Produces(restful.MIME_JSON, restful.MIME_XML) // you can specify this per route as well

      // 添加路由： GET /{user-id} --> u.findUser
    ws.Route(ws.GET("/{user-id}").To(u.findUser))
  
      // 添加路由： POST / --> u.updateUser
    ws.Route(ws.POST("").To(u.updateUser))
  
      // 添加路由： PUT /{user-id} --> u.createUser
    ws.Route(ws.PUT("/{user-id}").To(u.createUser))
  
      // 添加路由： DELETE /{user-id} --> u.removeUser
    ws.Route(ws.DELETE("/{user-id}").To(u.removeUser))

      // 将初始化好的WebService添加到Container中
    container.Add(ws)
}

// GET http://localhost:8080/users/1
//
func (u UserResource) findUser(request *restful.Request, response *restful.Response) {
    id := request.PathParameter("user-id")
    usr := u.users[id]
    if len(usr.Id) == 0 {
        response.AddHeader("Content-Type", "text/plain")
        response.WriteErrorString(http.StatusNotFound, "User could not be found.")
    } else {
        response.WriteEntity(usr)
    }
}

// POST http://localhost:8080/users
// <User><Id>1</Id><Name>Melissa Raspberry</Name></User>
//
func (u *UserResource) updateUser(request *restful.Request, response *restful.Response) {
    usr := new(User)
    err := request.ReadEntity(&usr)
    if err == nil {
        u.users[usr.Id] = *usr
        response.WriteEntity(usr)
    } else {
        response.AddHeader("Content-Type", "text/plain")
        response.WriteErrorString(http.StatusInternalServerError, err.Error())
    }
}

// PUT http://localhost:8080/users/1
// <User><Id>1</Id><Name>Melissa</Name></User>
//
func (u *UserResource) createUser(request *restful.Request, response *restful.Response) {
    usr := User{Id: request.PathParameter("user-id")}
    err := request.ReadEntity(&usr)
    if err == nil {
        u.users[usr.Id] = usr
        response.WriteHeader(http.StatusCreated)
        response.WriteEntity(usr)
    } else {
        response.AddHeader("Content-Type", "text/plain")
        response.WriteErrorString(http.StatusInternalServerError, err.Error())
    }
}

// DELETE http://localhost:8080/users/1
//
func (u *UserResource) removeUser(request *restful.Request, response *restful.Response) {
    id := request.PathParameter("user-id")
    delete(u.users, id)
}

func main() {
      // 创建一个空的Container
    wsContainer := restful.NewContainer()
  
    // 设定路由为CurlyRouter(快速路由)
    wsContainer.Router(restful.CurlyRouter{})
  
      // 创建自定义的Resource Handle(此处为UserResource)
    u := UserResource{map[string]User{}}
  
      // 创建WebService，并将WebService加入到Container中
    u.Register(wsContainer)

    log.Printf("start listening on localhost:8080")
    server := &http.Server{Addr: ":8080", Handler: wsContainer}
      
      // 启动服务
    log.Fatal(server.ListenAndServe())
}

上面的示例代码构建RESTful服务，分为几个步骤，apiServer也是类似：
1.创建Container
2.配置Container属性：ServeMux/Router type等
3.创建自定义的Resource Handle，实现Resource相关的处理方式。
4.创建对应Resource的WebService，在WebService中添加响应Route，并将WebService加入到Container中。
5.启动监听服务。

apiServer go-restful使用

Container初始化

apiServer的Container相关的结构是APIContainer。
路径：pkg/genericapiserver/mux/container.go

type APIContainer struct {
    *restful.Container
    NonSwaggerRoutes PathRecorderMux
    SecretRoutes     Mux
}

而该结构是在GenericAPIServer中被使用，分析过apiServer的启动过程的话，应该对该结构比较熟悉。

type GenericAPIServer struct {
    discoveryAddresses DiscoveryAddresses

    LoopbackClientConfig *restclient.Config

    minRequestTimeout time.Duration

    ...

    requestContextMapper api.RequestContextMapper

    // 这里使用到了restful.Container
    HandlerContainer *genericmux.APIContainer

    SecureServingInfo   *SecureServingInfo
    InsecureServingInfo *ServingInfo

    effectiveSecurePort, effectiveInsecurePort int

    ExternalAddress string

    storage map[string]rest.Storage

    Serializer runtime.NegotiatedSerializer

    Handler         http.Handler
    InsecureHandler http.Handler

    apiGroupsForDiscoveryLock sync.RWMutex
    apiGroupsForDiscovery     map[string]unversioned.APIGroup

    ...
}

而该结构的初始化是在master的初始化过程中进行的。
调用过程： main --> App.Run --> master.Complete.New --> c.Config.GenericConfig.SkipComplete().New()
路径： pkg/genericapiserver/config.go

func (c completedConfig) New() (*GenericAPIServer, error) {
    if c.Serializer == nil {
        return nil, fmt.Errorf("Genericapiserver.New() called with config.Serializer == nil")
    }

    s := &GenericAPIServer{
        discoveryAddresses:     c.DiscoveryAddresses,
        LoopbackClientConfig:   c.LoopbackClientConfig,
        legacyAPIGroupPrefixes: c.LegacyAPIGroupPrefixes,
        admissionControl:       c.AdmissionControl,
        requestContextMapper:   c.RequestContextMapper,
        Serializer:             c.Serializer,

        minRequestTimeout:    time.Duration(c.MinRequestTimeout) * time.Second,
        enableSwaggerSupport: c.EnableSwaggerSupport,

        SecureServingInfo:   c.SecureServingInfo,
        InsecureServingInfo: c.InsecureServingInfo,
        ExternalAddress:     c.ExternalAddress,

        apiGroupsForDiscovery: map[string]unversioned.APIGroup{},

        enableOpenAPISupport: c.EnableOpenAPISupport,
        openAPIConfig:        c.OpenAPIConfig,

        postStartHooks: map[string]postStartHookEntry{},
    }
    // 这里进行了Contianer的初始化
    s.HandlerContainer = mux.NewAPIContainer(http.NewServeMux(), c.Serializer)
    // 添加了DynamicApisDiscovery的
    s.installAPI(c.Config)

    s.Handler, s.InsecureHandler = c.BuildHandlerChainsFunc(s.HandlerContainer.ServeMux, c.Config)

    return s, nil
}

继续调用mux.NewAPIContainer()接口创建，该接口的两个参数：新建了一个http的ServeMux; 另一个是实现了编解码序列化反序列化的对象

func NewAPIContainer(mux *http.ServeMux, s runtime.NegotiatedSerializer) *APIContainer {
    c := APIContainer{
        // New一个Container
        Container: restful.NewContainer(),
        NonSwaggerRoutes: PathRecorderMux{
            mux: mux,
        },
        SecretRoutes: mux,
    }
    // 配置http.ServeMux
    c.Container.ServeMux = mux
    // 配置该Container的路由方式：CurlyRouter 即快速路由
    c.Container.Router(restful.CurlyRouter{}) // e.g. for proxy/{kind}/{name}/{*}
    // 配置panic产生之后的恢复处理函数
    apiserver.InstallRecoverHandler(s, c.Container)
    apiserver.InstallServiceErrorHandler(s, c.Container)

    return &c
}

看下apiserver.InstallRecoverHandler()实现：

func InstallRecoverHandler(s runtime.NegotiatedSerializer, container *restful.Container) {
    container.RecoverHandler(func(panicReason interface{}, httpWriter http.ResponseWriter) {
        logStackOnRecover(s, panicReason, httpWriter)
    })
}

// RecoverHandler changes the default function (logStackOnRecover) to be called
// when a panic is detected. DoNotRecover must be have its default value (=false).
func (c *Container) RecoverHandler(handler RecoverHandleFunction) {
    c.recoverHandleFunc = handler
}

根据英文注释可以看明白，该RecoverHandler就是在产生panic后会调用的恢复处理函数，默认的调用函数是logStackOnRecover,调用Container.RecoverHandler()后会修改该默认函数，并且Container.DoNotRecover的bool值必须是false才能生效。
apiserver.InstallServiceErrorHandler()接口就不看了，其实就是修改Service Error产生后的错误处理函数，默认是调用writeServiceError()。

到这里Container的初始化基本OK了。

添加WebService

Container已创建并且也进行了初始化。该轮到WebService了，这节会介绍k8s的WebService的创建及添加。
接续上文的Container初始化入口，继续往下看s.installAPI(c.Config):

func (s *GenericAPIServer) installAPI(c *Config) {
    // 这里原本还有很多routes.Install()函数
    // 这些install()貌似和mux有关。
    // 而mux就是一个http的多分器，用于派发某个Request路径到对应的http.Handler进行处理
    。。。
    // 往HandlerContainer中的Container里添加WebService
    // 该WebService的创建在s.DynamicApisDiscovery()中进行
    // 实际上创建的WebService是用于list 该group下的所有versions
    s.HandlerContainer.Add(s.DynamicApisDiscovery())
}

先看下WebService的创建接口s.DynamicApisDiscovery()：
路径：pkg/genericapiserver/genericapiserver.go

// DynamicApisDiscovery returns a webservice serving api group discovery.
// Note: during the server runtime apiGroupsForDiscovery might change.
func (s *GenericAPIServer) DynamicApisDiscovery() *restful.WebService {
    return apiserver.NewApisWebService(s.Serializer, APIGroupPrefix, func(req *restful.Request) []unversioned.APIGroup {
        // 需要加锁
        // 接口注释也有说明。因为k8s可以动态加载第三方apiGroups
        s.apiGroupsForDiscoveryLock.RLock()
        defer s.apiGroupsForDiscoveryLock.RUnlock()

        // 将apiGroupsForDiscovery中所有的APIGroup按照其名字进行升序排序
        sortedGroups := []unversioned.APIGroup{}
        groupNames := make([]string, 0, len(s.apiGroupsForDiscovery))
        for groupName := range s.apiGroupsForDiscovery {
            groupNames = append(groupNames, groupName)
        }
        sort.Strings(groupNames)
        for _, groupName := range groupNames {
            sortedGroups = append(sortedGroups, s.apiGroupsForDiscovery[groupName])
        }
        // 创建切片，并填充各个APIGroup的ServerAddressByClientCIDRs信息
        clientIP := utilnet.GetClientIP(req.Request)
        serverCIDR := s.discoveryAddresses.ServerAddressByClientCIDRs(clientIP)
        groups := make([]unversioned.APIGroup, len(sortedGroups))
        for i := range sortedGroups {
            groups[i] = sortedGroups[i]
            groups[i].ServerAddressByClientCIDRs = serverCIDR
        }
        return groups
    })
}

继续深入看apiserver.NewApisWebService()，该接口传入了编解码对象，APIGroup的Prefix，还有一个function。

func NewApisWebService(s runtime.NegotiatedSerializer, apiPrefix string, f func(req *restful.Request) []unversioned.APIGroup) *restful.WebService {
    // 用于向后兼容v1.1版本，返回一个空的APIGroup
    ss := StripVersionNegotiatedSerializer{s}
    // 获取支持的媒体类型,比如：application/json，application/yaml
    mediaTypes, _ := mediaTypesForSerializer(s)
    // 构建go-restful的Route处理方法
    rootAPIHandler := RootAPIHandler(ss, f)
    // 创建WebService
    ws := new(restful.WebService)
    // 添加Path
    ws.Path(apiPrefix)
    // API 说明
    ws.Doc("get available API versions")
    // 配置GET("/") 转到rootAPIHandler()接口
    ws.Route(ws.GET("/").To(rootAPIHandler).
        Doc("get available API versions").
        Operation("getAPIVersions").
        Produces(mediaTypes...).
        Consumes(mediaTypes...).
        Writes(unversioned.APIGroupList{}))
    return ws
}

到这里list某个Group下所有的versions的API已经注册完成了。
这些都不是关键的RESTful API的注册，关键的注册都会在pkg/apiserver/apiserver.go中的InstallREST()接口中进行。
琢磨过apiServer启动流程的同学，应该会知道/api和/apis的注册接口最后都会调用到该接口。
/api的注册接口是pkg/genericapiserver/genericapiserver.go中的InstallLegacyAPIGroup()接口
/apis的注册接口是InstallAPIGroup()。
这两个接口都会调用s.installAPIResources()，最后再调用apiGroupVersion.InstallREST()进行API注册。
流程基本就是这样，接着我们直接进入InstallREST()接口看实现：

func (g *APIGroupVersion) InstallREST(container *restful.Container) error {
    // 拼装path: "Prefix/Group/Version"    
    // 然后填充并返回一个APIInstaller对象
    installer := g.newInstaller()
    // 创建一个WebService
    ws := installer.NewWebService()
    // 这个是关键，会对各种URL进行注册
    apiResources, registrationErrors := installer.Install(ws)
    lister := g.ResourceLister
    if lister == nil {
        lister = staticLister{apiResources}
    }
    // 增加一个list的API
    AddSupportedResourcesWebService(g.Serializer, ws, g.GroupVersion, lister)
    // 将该WebService加入到Container
    container.Add(ws)
    return utilerrors.NewAggregate(registrationErrors)
}

前两个调用函数比较简单，这里不进行介绍了。直接进入关键函数installer.Install(ws)：

func (a *APIInstaller) Install(ws *restful.WebService) (apiResources []unversioned.APIResource, errors []error) {
    errors = make([]error, 0)

    proxyHandler := (&ProxyHandler{
        prefix:     a.prefix + "/proxy/",
        storage:    a.group.Storage,
        serializer: a.group.Serializer,
        mapper:     a.group.Context,
    })

    // 将所有的path合成一个切片，并按照升序重新排序
    paths := make([]string, len(a.group.Storage))
    var i int = 0
    for path := range a.group.Storage {
        paths[i] = path
        i++
    }
    sort.Strings(paths)
    for _, path := range paths {
        // 注册各个URL,关键接口
        // 传入的参数：path，rest.Storage，WebService，Handler
        apiResource, err := a.registerResourceHandlers(path, a.group.Storage[path], ws, proxyHandler)
        if err != nil {
            errors = append(errors, fmt.Errorf("error in registering resource: %s, %v", path, err))
        }
        // 将所有注册成功的Resource合成一个切片
        // 将该切片作为返回值，便于之后的接口注册list Resources的API
        if apiResource != nil {
            apiResources = append(apiResources, *apiResource)
        }
    }
    return apiResources, errors
}

该接口先是遍历所有的path，并升序重新排列，然后循环调用接口注册各个URL的API,并将这些注册成功的APIResource加入到同一个切片中。
我们继续看a.registerResourceHandlers()接口：

func (a *APIInstaller) registerResourceHandlers(path string, storage rest.Storage, ws *restful.WebService, proxyHandler http.Handler) (*unversioned.APIResource, error) {
    ...

    // 构建creater、lister、deleter、updater、watcher等，其实就是storage
    creater, isCreater := storage.(rest.Creater)
    namedCreater, isNamedCreater := storage.(rest.NamedCreater)
    lister, isLister := storage.(rest.Lister)
    getter, isGetter := storage.(rest.Getter)
    getterWithOptions, isGetterWithOptions := storage.(rest.GetterWithOptions)
    deleter, isDeleter := storage.(rest.Deleter)
    gracefulDeleter, isGracefulDeleter := storage.(rest.GracefulDeleter)
    collectionDeleter, isCollectionDeleter := storage.(rest.CollectionDeleter)
    updater, isUpdater := storage.(rest.Updater)
    patcher, isPatcher := storage.(rest.Patcher)
    watcher, isWatcher := storage.(rest.Watcher)
    _, isRedirector := storage.(rest.Redirector)
    connecter, isConnecter := storage.(rest.Connecter)
    storageMeta, isMetadata := storage.(rest.StorageMetadata)
    ...
    var apiResource unversioned.APIResource
    // k8s资源分为两类：无namespace的RESTScopeNameRoot; 有namespace的RESTScopeNameNamespace
    // 在对应的path上添加各类actions，并指定对应的handler。
    switch scope.Name() {
    case meta.RESTScopeNameRoot:
        // Handle non-namespace scoped resources like nodes.
        resourcePath := resource
        resourceParams := params
        itemPath := resourcePath + "/{name}"
        nameParams := append(params, nameParam)
        proxyParams := append(nameParams, pathParam)
        suffix := ""
        if hasSubresource {
            suffix = "/" + subresource
            itemPath = itemPath + suffix
            resourcePath = itemPath
            resourceParams = nameParams
        }
        apiResource.Name = path
        apiResource.Namespaced = false
        apiResource.Kind = resourceKind
        namer := rootScopeNaming{scope, a.group.Linker, gpath.Join(a.prefix, resourcePath, "/"), suffix}

        // Handler for standard REST verbs (GET, PUT, POST and DELETE).
        // Add actions at the resource path: /api/apiVersion/resource
        actions = appendIf(actions, action{"LIST", resourcePath, resourceParams, namer, false}, isLister)
        actions = appendIf(actions, action{"POST", resourcePath, resourceParams, namer, false}, isCreater)
        actions = appendIf(actions, action{"DELETECOLLECTION", resourcePath, resourceParams, namer, false}, isCollectionDeleter)
        // DEPRECATED
        actions = appendIf(actions, action{"WATCHLIST", "watch/" + resourcePath, resourceParams, namer, false}, allowWatchList)

        // Add actions at the item path: /api/apiVersion/resource/{name}
        actions = appendIf(actions, action{"GET", itemPath, nameParams, namer, false}, isGetter)
        if getSubpath {
            actions = appendIf(actions, action{"GET", itemPath + "/{path:*}", proxyParams, namer, false}, isGetter)
        }
        actions = appendIf(actions, action{"PUT", itemPath, nameParams, namer, false}, isUpdater)
        actions = appendIf(actions, action{"PATCH", itemPath, nameParams, namer, false}, isPatcher)
        actions = appendIf(actions, action{"DELETE", itemPath, nameParams, namer, false}, isDeleter)
        actions = appendIf(actions, action{"WATCH", "watch/" + itemPath, nameParams, namer, false}, isWatcher)
        // We add "proxy" subresource to remove the need for the generic top level prefix proxy.
        // The generic top level prefix proxy is deprecated in v1.2, and will be removed in 1.3, or 1.4 at the latest.
        // TODO: DEPRECATED in v1.2.
        actions = appendIf(actions, action{"PROXY", "proxy/" + itemPath + "/{path:*}", proxyParams, namer, false}, isRedirector)
        // TODO: DEPRECATED in v1.2.
        actions = appendIf(actions, action{"PROXY", "proxy/" + itemPath, nameParams, namer, false}, isRedirector)
        actions = appendIf(actions, action{"CONNECT", itemPath, nameParams, namer, false}, isConnecter)
        actions = appendIf(actions, action{"CONNECT", itemPath + "/{path:*}", proxyParams, namer, false}, isConnecter && connectSubpath)
        break
    case meta.RESTScopeNameNamespace:
        ...
        break
    default:
        return nil, fmt.Errorf("unsupported restscope: %s", scope.Name())
    }

    ...
    // 根据之前生成的actions,进行遍历
    // 然后在WebService中添加指定的route
    for _, action := range actions {
        versionedObject := storageMeta.ProducesObject(action.Verb)
        if versionedObject == nil {
            versionedObject = defaultVersionedObject
        }
        reqScope.Namer = action.Namer
        namespaced := ""
        if apiResource.Namespaced {
            namespaced = "Namespaced"
        }
        operationSuffix := ""
        if strings.HasSuffix(action.Path, "/{path:*}") {
            operationSuffix = operationSuffix + "WithPath"
        }
        if action.AllNamespaces {
            operationSuffix = operationSuffix + "ForAllNamespaces"
            namespaced = ""
        }
        // 判断action的动作类型
        // 生成响应的handler，创建route添加到WebService中
        switch action.Verb {
        case "GET": // Get a resource.
            var handler restful.RouteFunction
            // 判断是否有参数
            if isGetterWithOptions {
                handler = GetResourceWithOptions(getterWithOptions, reqScope)
            } else {
                handler = GetResource(getter, exporter, reqScope)
            }
            // 生成处理函数
            handler = metrics.InstrumentRouteFunc(action.Verb, resource, handler)
            doc := "read the specified " + kind
            if hasSubresource {
                doc = "read " + subresource + " of the specified " + kind
            }
            route := ws.GET(action.Path).To(handler).
                Doc(doc).
                Param(ws.QueryParameter("pretty", "If 'true', then the output is pretty printed.")).
                Operation("read"+namespaced+kind+strings.Title(subresource)+operationSuffix).
                Produces(append(storageMeta.ProducesMIMETypes(action.Verb), mediaTypes...)...).
                Returns(http.StatusOK, "OK", versionedObject).
                Writes(versionedObject)
            if isGetterWithOptions {
                if err := addObjectParams(ws, route, versionedGetOptions); err != nil {
                    return nil, err
                }
            }
            if isExporter {
                if err := addObjectParams(ws, route, versionedExportOptions); err != nil {
                    return nil, err
                }
            }
            addParams(route, action.Params)
            ws.Route(route)
        case "LIST": // List all resources of a kind.
            ...
        case "PUT": // Update a resource.
            ...
        case "PATCH": // Partially update a resource
            ...
        case "POST": // Create a resource.
            ...
        case "DELETE": // Delete a resource.
            ...
        case "DELETECOLLECTION":
            ...
        case "WATCH": // Watch a resource.
            ...
        case "WATCHLIST": // Watch all resources of a kind.
            ...
        case "PROXY": // Proxy requests to a resource.
            ...
        case "CONNECT":
            ...
            }
        default:
            return nil, fmt.Errorf("unrecognized action verb: %s", action.Verb)
        }
        // Note: update GetAttribs() when adding a custom handler.
    }
    return &apiResource, nil
}

首先构建creater、lister、getter、deleter、updater、patcher、watcher，其实他们都是storage，只是对应着对etcd的不同操作。
然后针对所有的action，构建响应的handler。创建对应的route,最后把route添加到service里面。这样就完成了api的注册。

关键的REST API注册基本就这样结束了，除此之外还会有很多别的API的注册：
比如APIGroupVersion.InstallREST()接口中的AddSupportedResourcesWebService(g.Serializer, ws, g.GroupVersion, lister)；
GenericAPIServer.InstallLegacyAPIGroup()接口中的apiserver.AddApiWebService()的调用；
等等。。
其实上面也注册了各种REST API，比如像PodList,ServiceList,ReplicationControllerList等。这些就不深入了，都是大同小异。

参考资料

1.go-restful example: http://ernestmicklei.com/2012...
2.go-restful api desgin: http://ernestmicklei.com/2012...
3.go-restful github code： https://github.com/emicklei/g...
4.go-restful GoDoc: https://godoc.org/github.com/...