Kubernetes1.5源码分析(二) apiServer之资源注册

摘要：我们先将上面的接口解析放放，先看下是如何初始化的路径定义了，再看路径定义空的创建，用于不同版本对象转换增加一些转换函数上面就创建了一个空的。其实就是向添加了转换函数，比如将转换为，将转换为。

Kubernetes v1.5.0

k8s里面有各种资源，如Pod、Service、RC、namespaces等资源，用户操作的其实也就是这一大堆资源。但这些资源并不是杂乱无章的，使用了GroupVersion的方式组织在一起。每一种资源都属于一个Group，而资源还有版本之分，如v1、v1beta1等。
k8s目前正在使用的API groups：

"core" group：它的REST path是api/v1

"extensions" group：它的REST path是/apis/extensions/v1beta1

"autoscaling", "abac" ...

服务器的URL的格式：/prefix/group/version/... (例如：/apis/extensions/v1beta1)

APIGroupVersion：对API资源的组织，里面包含了Storage、GroupVersion、Mapper、Serializer、Convertor等成员。Storage是etcd的接口，这是一个map类型，每一种资源都会与etcd建立一个连接；GroupVersion表示该APIGroupVersion属于哪个Group、哪个version；Serializer用于序列化，反序列化；Convertor提供各个不同版本进行转化的接口；Mapper实现了RESTMapper接口。

type APIGroupVersion struct {
    // key存在对象的url，value是一个rest.Storage，用于对接etcd存储
    Storage map[string]rest.Storage
    // 该group的prefix，例如核心组的Root是"/api"
    Root string

    // 包含类似"api/v1"这样的string，用于标识这个实例
    GroupVersion unversioned.GroupVersion

    // OptionsExternalVersion controls the Kubernetes APIVersion used for common objects in the apiserver
    // schema like api.Status, api.DeleteOptions, and api.ListOptions. Other implementors may
    // define a version "v1beta1" but want to use the Kubernetes "v1" internal objects. If
    // empty, defaults to GroupVersion.
    OptionsExternalVersion *unversioned.GroupVersion

    // 关键性成员
    Mapper meta.RESTMapper

    // 对象序列化和反序列化器
    Serializer     runtime.NegotiatedSerializer
    ParameterCodec runtime.ParameterCodec

    // 以下4个都是被赋值为Scheme结构
    Typer     runtime.ObjectTyper
    Creater   runtime.ObjectCreater
    // 相互转换任意api版本的对象，需要事先注册转换函数
    Convertor runtime.ObjectConvertor
    Copier    runtime.ObjectCopier

    Linker    runtime.SelfLinker

    // 用于访问许可控制
    Admit   admission.Interface
    Context api.RequestContextMapper

    MinRequestTimeout time.Duration

    // SubresourceGroupVersionKind contains the GroupVersionKind overrides for each subresource that is
    // accessible from this API group version. The GroupVersionKind is that of the external version of
    // the subresource. The key of this map should be the path of the subresource. The keys here should
    // match the keys in the Storage map above for subresources.
    SubresourceGroupVersionKind map[string]unversioned.GroupVersionKind

    // ResourceLister is an interface that knows how to list resources
    // for this API Group.
    ResourceLister APIResourceLister
}

APIGroupVersion的创建接口是pkg/genericapiserver/genericapiserver.go中的newAPIGroupVersion()接口，在接口在创建APIGroupVersion还用到了好几个别的结构：APIGroupInfo、Scheme、GroupMeta。下面一个一个介绍：
APIGroupInfo:

type APIGroupInfo struct {
    // 该Group的元信息
    GroupMeta apimachinery.GroupMeta
    // 不同版本的所有的Storage
    VersionedResourcesStorageMap map[string]map[string]rest.Storage
    // OptionsExternalVersion controls the APIVersion used for common objects in the
    // schema like api.Status, api.DeleteOptions, and api.ListOptions. Other implementors may
    // define a version "v1beta1" but want to use the Kubernetes "v1" internal objects.
    // If nil, defaults to groupMeta.GroupVersion.
    // TODO: Remove this when https://github.com/kubernetes/kubernetes/issues/19018 is fixed.
    OptionsExternalVersion *unversioned.GroupVersion

    // core group的话，对应的就是api.Scheme
    Scheme *runtime.Scheme
    // NegotiatedSerializer controls how this group encodes and decodes data
    NegotiatedSerializer runtime.NegotiatedSerializer
    // ParameterCodec performs conversions for query parameters passed to API calls
    ParameterCodec runtime.ParameterCodec

    // 所有resources信息,key就是resource的path
    // 比如：key为"replicationcontrollers/scale",GroupVersionKind: autoscaling, v1, Scale
    SubresourceGroupVersionKind map[string]unversioned.GroupVersionKind
}

Scheme: 用于API资源之间的序列化、反序列化、版本转换。Scheme里面还有好几个map，前面的结构体存储的都是unversioned.GroupVersionKind、unversioned.GroupVersion这些东西，这些东西本质上只是表示资源的字符串标识，Scheme存储了对应着标志的具体的API资源的结构体，即relect.Type

type Scheme struct {
    // versionMap allows one to figure out the go type of an object with
    // the given version and name.
    gvkToType map[unversioned.GroupVersionKind]reflect.Type

    // typeToGroupVersion allows one to find metadata for a given go object.
    // The reflect.Type we index by should *not* be a pointer.
    typeToGVK map[reflect.Type][]unversioned.GroupVersionKind

    // unversionedTypes are transformed without conversion in ConvertToVersion.
    unversionedTypes map[reflect.Type]unversioned.GroupVersionKind

    // unversionedKinds are the names of kinds that can be created in the context of any group
    // or version
    // TODO: resolve the status of unversioned types.
    unversionedKinds map[string]reflect.Type

    // Map from version and resource to the corresponding func to convert
    // resource field labels in that version to internal version.
    fieldLabelConversionFuncs map[string]map[string]FieldLabelConversionFunc

    // defaulterFuncs is an array of interfaces to be called with an object to provide defaulting
    // the provided object must be a pointer.
    defaulterFuncs map[reflect.Type]func(interface{})

    // converter stores all registered conversion functions. It also has
    // default coverting behavior.
    converter *conversion.Converter

    // cloner stores all registered copy functions. It also has default
    // deep copy behavior.
    cloner *conversion.Cloner
}

GroupMeta： 主要包括Group的元信息，里面的成员RESTMapper，与APIGroupVersion一样，其实APIGroupVersion的RESTMapper直接取之于GroupMeta的RESTMapper.一个Group可能包含多个版本，存储在GroupVersion中，而GroupVersion是默认存储在etcd中的版本。

type GroupMeta struct {
    // 默认版本
    GroupVersion unversioned.GroupVersion

    // 该Group中可能会有多个版本，该字段就包含了所有的versions
    GroupVersions []unversioned.GroupVersion

    // 用于编解码
    Codec runtime.Codec

    // SelfLinker can set or get the SelfLink field of all API types.
    // TODO: when versioning changes, make this part of each API definition.
    // TODO(lavalamp): Combine SelfLinker & ResourceVersioner interfaces, force all uses
    // to go through the InterfacesFor method below.
    SelfLinker runtime.SelfLinker

    // 用于类型，对象之间的转换
    RESTMapper meta.RESTMapper

    // InterfacesFor returns the default Codec and ResourceVersioner for a given version
    // string, or an error if the version is not known.
    // TODO: make this stop being a func pointer and always use the default
    // function provided below once every place that populates this field has been changed.
    InterfacesFor func(version unversioned.GroupVersion) (*meta.VersionInterfaces, error)

    // InterfacesByVersion stores the per-version interfaces.
    InterfacesByVersion map[unversioned.GroupVersion]*meta.VersionInterfaces
}

RESTMapper： 用于管理所有对象的信息。外部要获取的话，直接通过version,group获取到RESTMapper，然后通过kind类型可以获取到对应的信息。该RESTMapper其实是实现了一个DefaultRESTMapper结构。

type DefaultRESTMapper struct {
    defaultGroupVersions []unversioned.GroupVersion

    resourceToKind       map[unversioned.GroupVersionResource]unversioned.GroupVersionKind
    kindToPluralResource map[unversioned.GroupVersionKind]unversioned.GroupVersionResource
    kindToScope          map[unversioned.GroupVersionKind]RESTScope
    singularToPlural     map[unversioned.GroupVersionResource]unversioned.GroupVersionResource
    pluralToSingular     map[unversioned.GroupVersionResource]unversioned.GroupVersionResource

    interfacesFunc VersionInterfacesFunc

    // aliasToResource is used for mapping aliases to resources
    aliasToResource map[string][]string
}

APIRegistrationManager：这个结构体主要提供了已经"registered"的概念，将所有已经注册的，已经激活的，第三方的的GroupVersions进行了汇总，还包括了各个GroupVersion的GroupMeta(元数据)。

type APIRegistrationManager struct {
    // 所以已经registered的GroupVersions
    registeredVersions map[unversioned.GroupVersion]struct{}

    // 第三方注册的GroupVersions,这些都向apiServer动态注册的
    thirdPartyGroupVersions []unversioned.GroupVersion

    // 所有已经enable的GroupVersions，可以通过EnableVersions()将要enable的GroupVersion加入进来。
    // 只有enable了，才能使用对应的GroupVersion
    enabledVersions map[unversioned.GroupVersion]struct{}

    // 所有groups的GroupMeta
    groupMetaMap map[string]*apimachinery.GroupMeta
    // 跟环境变量"KUBE_API_VERSIONS"有关
    envRequestedVersions []unversioned.GroupVersion
}

该结构的路径：pkg/apimachinery/registered/registered.go
在该文件中我们能看到初始化了一个DefaultAPIRegistrationManager对象：

var (
    DefaultAPIRegistrationManager = NewOrDie(os.Getenv("KUBE_API_VERSIONS"))
)

进入NewOrDie()接口看下：

func NewOrDie(kubeAPIVersions string) *APIRegistrationManager {
    m, err := NewAPIRegistrationManager(kubeAPIVersions)
    if err != nil {
        glog.Fatalf("Could not construct version manager: %v (KUBE_API_VERSIONS=%q)", err, kubeAPIVersions)
    }
    return m
}

func NewAPIRegistrationManager(kubeAPIVersions string) (*APIRegistrationManager, error) {
    m := &APIRegistrationManager{
        registeredVersions:      map[unversioned.GroupVersion]struct{}{},
        thirdPartyGroupVersions: []unversioned.GroupVersion{},
        enabledVersions:         map[unversioned.GroupVersion]struct{}{},
        groupMetaMap:            map[string]*apimachinery.GroupMeta{},
        envRequestedVersions:    []unversioned.GroupVersion{},
    }

    // 如果环境变量KUBE_API_VERSIONS进行了设置的话，进行遍历
    if len(kubeAPIVersions) != 0 {
        // 通过逗号进行分隔
        for _, version := range strings.Split(kubeAPIVersions, ",") {
            // 解析version并转换成GroupVersion格式
            // 一般这里的version是group/version格式，比如"/api/v1"
            gv, err := unversioned.ParseGroupVersion(version)
            if err != nil {
                return nil, fmt.Errorf("invalid api version: %s in KUBE_API_VERSIONS: %s.",
                    version, kubeAPIVersions)
            }
            // 然后将该gv放入envRequestedVersions
            m.envRequestedVersions = append(m.envRequestedVersions, gv)
        }
    }
    // 否则返回一个空的APIRegistrationManager
    return m, nil
}

瞅了下我们正在使用的环境，没有配置KUBE_API_VERSIONS,即返回了一个空的结构，还提供了好多方法。

var (
    ValidateEnvRequestedVersions  = DefaultAPIRegistrationManager.ValidateEnvRequestedVersions
    AllPreferredGroupVersions     = DefaultAPIRegistrationManager.AllPreferredGroupVersions
    RESTMapper                    = DefaultAPIRegistrationManager.RESTMapper
    GroupOrDie                    = DefaultAPIRegistrationManager.GroupOrDie
    AddThirdPartyAPIGroupVersions = DefaultAPIRegistrationManager.AddThirdPartyAPIGroupVersions
    IsThirdPartyAPIGroupVersion   = DefaultAPIRegistrationManager.IsThirdPartyAPIGroupVersion
    RegisteredGroupVersions       = DefaultAPIRegistrationManager.RegisteredGroupVersions
    IsRegisteredVersion           = DefaultAPIRegistrationManager.IsRegisteredVersion
    IsRegistered                  = DefaultAPIRegistrationManager.IsRegistered
    Group                         = DefaultAPIRegistrationManager.Group
    EnabledVersionsForGroup       = DefaultAPIRegistrationManager.EnabledVersionsForGroup
    EnabledVersions               = DefaultAPIRegistrationManager.EnabledVersions
    IsEnabledVersion              = DefaultAPIRegistrationManager.IsEnabledVersion
    IsAllowedVersion              = DefaultAPIRegistrationManager.IsAllowedVersion
    EnableVersions                = DefaultAPIRegistrationManager.EnableVersions
    RegisterGroup                 = DefaultAPIRegistrationManager.RegisterGroup
    RegisterVersions              = DefaultAPIRegistrationManager.RegisterVersions
    InterfacesFor                 = DefaultAPIRegistrationManager.InterfacesFor
)

在分析apiServer的启动流程的时候，你会发现初始化ServerRunOptions对象时，用到了好多上面的变量，比如：
路径：pkg/genericapiserver/options/server_run_options.go

func NewServerRunOptions() *ServerRunOptions {
    return &ServerRunOptions{
        AdmissionControl:                         "AlwaysAdmit",
。。。
        // 这里就使用了AllPreferredGroupVersions接口
        DefaultStorageVersions:                   registered.AllPreferredGroupVersions(),
。。。
        StorageVersions:                          registered.AllPreferredGroupVersions(),
    }
}

上面就使用到了registered.AllPreferredGroupVersions()接口,顺便看下接口具体实现：

func (m *APIRegistrationManager) AllPreferredGroupVersions() string {
    // 如果没有注册groupMeta的话，这里就==0
    // 不过不可能没有注册，至于在哪里进行注册就得看下后面介绍的GroupMeta初始化了
    if len(m.groupMetaMap) == 0 {
        return ""
    }
    var defaults []string
    for _, groupMeta := range m.groupMetaMap {
        defaults = append(defaults, groupMeta.GroupVersion.String())
    }
    sort.Strings(defaults)
    return strings.Join(defaults, ",")
}

该接口比较简单，就是从m.groupMetaMap中取出所有的groupMeta，然后通过逗号拼接成"group1/version1,group2/version2,..."的字符串。

这里可以想一下，既然有list，那总得有groupMeta啊。而我们看APIRegistrationManager的初始化，如果没有设置KUBE_API_VERSIONS环境变量的话，根本就没有groupMeta。
既然不可能没有groupMeta，那肯定得从别的地方进行register & enable。我们可以从APIRegistrationManager提供的RegisterGroup方法入手：

func (m *APIRegistrationManager) RegisterGroup(groupMeta apimachinery.GroupMeta) error {
    groupName := groupMeta.GroupVersion.Group
    if _, found := m.groupMetaMap[groupName]; found {
        return fmt.Errorf("group %v is already registered", m.groupMetaMap)
    }
    m.groupMetaMap[groupName] = &groupMeta
    return nil
}

该RegisterGroup接口的入参就是GroupMeta,所以我们得继续查看该结构的初始化了。

k8s现阶段，API一共分为13个Group：Core、apps、authentication、authorization、autoscaling、batch、certificates、componentconfig、extensions、imagepolicy、policy、rbac、storage。其中Core的Group Name为空，它包含的API是最核心的API,如Pod、Service等，它的代码位于pkg/api下面，其它12个Group代码位于pkg/apis。每个目录下都有一个install目录，里面有一个install.go文件，接着通过init()负责初始化。这些程序都是通过下列文件进行import：
路径： pkg/master/import_known_versions.go

package master

// These imports are the API groups the API server will support.
import (
    "fmt"

    _ "k8s.io/kubernetes/pkg/api/install"
    "k8s.io/kubernetes/pkg/apimachinery/registered"
    _ "k8s.io/kubernetes/pkg/apis/apps/install"
    _ "k8s.io/kubernetes/pkg/apis/authentication/install"
    _ "k8s.io/kubernetes/pkg/apis/authorization/install"
    _ "k8s.io/kubernetes/pkg/apis/autoscaling/install"
    _ "k8s.io/kubernetes/pkg/apis/batch/install"
    _ "k8s.io/kubernetes/pkg/apis/certificates/install"
    _ "k8s.io/kubernetes/pkg/apis/componentconfig/install"
    _ "k8s.io/kubernetes/pkg/apis/extensions/install"
    _ "k8s.io/kubernetes/pkg/apis/imagepolicy/install"
    _ "k8s.io/kubernetes/pkg/apis/policy/install"
    _ "k8s.io/kubernetes/pkg/apis/rbac/install"
    _ "k8s.io/kubernetes/pkg/apis/storage/install"
)

一共import了13个group。其中"k8s.io/kubernetes/pkg/api/install"就是Core Group，我们就以它为例，查看下对应的install.go文件。
路径： pkg/api/install/install.go

var availableVersions = []unversioned.GroupVersion{v1.SchemeGroupVersion}

func init() {
    // 进行Versions注册，其实就是存入APIRegistrationManager.registeredVersions中
    registered.RegisterVersions(availableVersions)
    externalVersions := []unversioned.GroupVersion{}
    for _, v := range availableVersions {
        // 判断下是否已经注册，并追加成一个切片
        if registered.IsAllowedVersion(v) {
            externalVersions = append(externalVersions, v)
        }
    }
    if len(externalVersions) == 0 {
        glog.V(4).Infof("No version is registered for group %v", api.GroupName)
        return
    }

    // 再进行enable，其实就是存入APIRegistrationManager.enabledVersions
    if err := registered.EnableVersions(externalVersions...); err != nil {
        glog.V(4).Infof("%v", err)
        return
    }
    // 该接口比较关键，进行多带带介绍
    if err := enableVersions(externalVersions); err != nil {
        glog.V(4).Infof("%v", err)
        return
    }
}

首先定义了一个切片availableVersions，里面只有一个元素v1.SchemeGroupVersion:

const GroupName = ""
var SchemeGroupVersion = unversioned.GroupVersion{Group: GroupName, Version: "v1"}

根据该元素的定义，可以看出availableVersions就定义了一个GroupName为空，Version是"v1"的GroupVersion。接着把该GroupVersion放入APIRegistrationManager的registeredVersions和enabledVersions中。
registered的几个接口实现比较简单不进行介绍了，但是执行的enableVersions()是重头戏，我们继续深入：

func enableVersions(externalVersions []unversioned.GroupVersion) error {
    // 字面意思：将所有的Versions添加到Scheme
    // 又牵扯到Scheme，后面会介绍Scheme的初始化
    // 越深入看牵扯出的概念越多，该接口也很重要，需要耐心层层挖掘
    addVersionsToScheme(externalVersions...)
    // 将一个GroupVersion作为默认的,即"/api/v1"
    preferredExternalVersion := externalVersions[0]

    // 就是这里！ 进行了GroupMeta的初始化。这就是我们这小节要看的关键
    groupMeta := apimachinery.GroupMeta{
        GroupVersion:  preferredExternalVersion,
        GroupVersions: externalVersions,
        // RESTMapper也是关键所在，下面也会单做一节进行介绍
        RESTMapper:    newRESTMapper(externalVersions),
        SelfLinker:    runtime.SelfLinker(accessor),
        InterfacesFor: interfacesFor,
    }

    // 前面都是register和enable了versions，这里才是进行了Group的register
    // 该接口其实就是以第一个GroupVersion的groupName为key，groupMeta为value
    // 对APIRegistrationManager的groupMetaMap,进行了赋值
    if err := registered.RegisterGroup(groupMeta); err != nil {
        return err
    }
    return nil
}

到这步，我们再结合之前APIRegistrationManager的初始化，就能知道groupMetaMap中应该有了好几组groupMeta。那在ServerRunOptions对象初始化中调用的registered.AllPreferredGroupVersions()接口,能返回好几个DefaultStorageVersions，至少肯定有"/api/v1"。至于别的groupMeta，需要再看下别的install.go，大同小异就不展开一个一个讲了。

groupMeta的初始化虽然结束了，但是这里又引出一个关键Scheme，那么继续下一小节吧。。

在上一节介绍enableVersions()函数时，第一行便是调用了addVersionsToScheme(externalVersions...),将GroupVersions加到Scheme。我们就来看下该接口:

func addVersionsToScheme(externalVersions ...unversioned.GroupVersion) {
    // add the internal version to Scheme
    if err := api.AddToScheme(api.Scheme); err != nil {
        // Programmer error, detect immediately
        panic(err)
    }
    // add the enabled external versions to Scheme
    for _, v := range externalVersions {
        if !registered.IsEnabledVersion(v) {
            glog.Errorf("Version %s is not enabled, so it will not be added to the Scheme.", v)
            continue
        }
        switch v {
        case v1.SchemeGroupVersion:
            if err := v1.AddToScheme(api.Scheme); err != nil {
                // Programmer error, detect immediately
                panic(err)
            }
        }
    }
}

接口中我们可以看到AddToScheme(api.Scheme)都是将GroupVersion加入到api.Scheme。我们先将上面的接口解析放放，先看下api.Scheme是如何初始化的：
路径：pkg/api/register.go

var Scheme = runtime.NewScheme()

定义了Scheme，再看NewScheme()：
路径：pkg/runtime/scheme.go

func NewScheme() *Scheme {
    // 定义空的Scheme
    s := &Scheme{
        gvkToType:        map[unversioned.GroupVersionKind]reflect.Type{},
        typeToGVK:        map[reflect.Type][]unversioned.GroupVersionKind{},
        unversionedTypes: map[reflect.Type]unversioned.GroupVersionKind{},
        unversionedKinds: map[string]reflect.Type{},
        cloner:           conversion.NewCloner(),
        fieldLabelConversionFuncs: map[string]map[string]FieldLabelConversionFunc{},
        defaulterFuncs:            map[reflect.Type]func(interface{}){},
    }
    // 创建converter，用于不同版本对象转换
    s.converter = conversion.NewConverter(s.nameFunc)
    // 增加一些转换函数
    s.AddConversionFuncs(DefaultEmbeddedConversions()...)

    // Enable map[string][]string conversions by default
    if err := s.AddConversionFuncs(DefaultStringConversions...); err != nil {
        panic(err)
    }
    if err := s.RegisterInputDefaults(&map[string][]string{}, JSONKeyMapper, conversion.AllowDifferentFieldTypeNames|conversion.IgnoreMissingFields); err != nil {
        panic(err)
    }
    if err := s.RegisterInputDefaults(&url.Values{}, JSONKeyMapper, conversion.AllowDifferentFieldTypeNames|conversion.IgnoreMissingFields); err != nil {
        panic(err)
    }
    return s
}

上面就创建了一个空的Scheme。
知道哪里创建Scheme后，我们继续回到上面的addVersionsToScheme()函数。
其实主要就是看两个接口: api.AddToScheme()和v1.AddToScheme()。
先看第一个：

var (
    SchemeBuilder = runtime.NewSchemeBuilder(addKnownTypes, addDefaultingFuncs)
    AddToScheme   = SchemeBuilder.AddToScheme
)

通过runtime.NewSchemeBuilder()接口传入两个函数，然后创建了SchemeBuilder：

type SchemeBuilder []func(*Scheme) error

func (sb *SchemeBuilder) Register(funcs ...func(*Scheme) error) {
    for _, f := range funcs {
        *sb = append(*sb, f)
    }
}


func NewSchemeBuilder(funcs ...func(*Scheme) error) SchemeBuilder {
    var sb SchemeBuilder
    sb.Register(funcs...)
    return sb
}

根据上面的定义和函数可以看出，SchemeBuilder就是一个接口切片，包含了addKnownTypes, addDefaultingFuncs两个接口。
SchemeBuilder定义好了之后，继续看AddToScheme:

func (sb *SchemeBuilder) AddToScheme(s *Scheme) error {
    for _, f := range *sb {
        if err := f(s); err != nil {
            return err
        }
    }
    return nil
}

该函数就是调用了addKnownTypes, addDefaultingFuncs两个接口,我们一个一个看：

func addKnownTypes(scheme *runtime.Scheme) error {
    if err := scheme.AddIgnoredConversionType(&unversioned.TypeMeta{}, &unversioned.TypeMeta{}); err != nil {
        return err
    }
    // 把下列对象加入到Scheme中
    // 该SchemeGroupVersion的GroupName为空，Version是"__internal"
    // 所以该接口其实是把k8s内置的version添加到Scheme，而且每个group都有该步
    scheme.AddKnownTypes(SchemeGroupVersion,
        &Pod{},
        &PodList{},
        &PodStatusResult{},
        &PodTemplate{},
        &PodTemplateList{},
        &ReplicationControllerList{},
        &ReplicationController{},
        &ServiceList{},
        &Service{},
        &ServiceProxyOptions{},
        &NodeList{},
        &Node{},
        &NodeProxyOptions{},
        &Endpoints{},
        &EndpointsList{},
        &Binding{},
        &Event{},
        &EventList{},
        &List{},
        &LimitRange{},
        &LimitRangeList{},
        &ResourceQuota{},
        &ResourceQuotaList{},
        &Namespace{},
        &NamespaceList{},
        &ServiceAccount{},
        &ServiceAccountList{},
        &Secret{},
        &SecretList{},
        &PersistentVolume{},
        &PersistentVolumeList{},
        &PersistentVolumeClaim{},
        &PersistentVolumeClaimList{},
        &DeleteOptions{},
        &ListOptions{},
        &PodAttachOptions{},
        &PodLogOptions{},
        &PodExecOptions{},
        &PodProxyOptions{},
        &ComponentStatus{},
        &ComponentStatusList{},
        &SerializedReference{},
        &RangeAllocation{},
        &ConfigMap{},
        &ConfigMapList{},
    )

    // 在GroupName为空，Version为"v1"的groupVersion中，添加这些对象到Scheme
    scheme.AddUnversionedTypes(Unversioned,
        &unversioned.ExportOptions{},
        &unversioned.Status{},
        &unversioned.APIVersions{},
        &unversioned.APIGroupList{},
        &unversioned.APIGroup{},
        &unversioned.APIResourceList{},
    )
    return nil
}

查看AddKnownTypes()接口：

func (s *Scheme) AddKnownTypes(gv unversioned.GroupVersion, types ...Object) {
    if len(gv.Version) == 0 {
        panic(fmt.Sprintf("version is required on all types: %s %v", gv, types[0]))
    }
    for _, obj := range types {
        t := reflect.TypeOf(obj)
        if t.Kind() != reflect.Ptr {
            panic("All types must be pointers to structs.")
        }
        t = t.Elem()
        if t.Kind() != reflect.Struct {
            panic("All types must be pointers to structs.")
        }

        gvk := gv.WithKind(t.Name())
        s.gvkToType[gvk] = t
        s.typeToGVK[t] = append(s.typeToGVK[t], gvk)
    }
}

该接口主要操作了s.gvkToType和s.typeToGVK，用于转换的目的。
综上得出，是将internal version添加到Scheme中。
为什么会有一个internal version呢？ 其实每一个Group都有一个internal version。而apiserver操作的也都是internal version.
举个例子：假如有一个创建Pod的请求来了，apiserver首先会将请求给反序列化，用户发过来的Pod请求往往是有版本的，比如v1，因此会反序列化为一个v1.Pod。apiserver会立即将这个v1.Pod利用convertor转换成internal.Pod，然后进行一些操作，最后要把它存到etcd里面去，etcd里面的Pod信息是有版本的，因此会先发生一次转换，将其转换为v1.Pod，然后序列化存入etcd。
这样看上去好像多此一举？其实这就是k8s对api多版本的支持，这样用户可以以一个v1beta1创建一个Pod,然后存入etcd的是一个相对稳定的版本，比如v1版本。

internal version添加完成后，继续回到最开始的addVersionsToScheme()函数，还要继续执行v1.AddToScheme(api.Scheme)函数.其实就是把v1版本的api添加到Scheme中，和添加internal版本一样。
我们看看v1.AddToScheme。
路径：pkg/api/v1/register.go

var (
    SchemeBuilder = runtime.NewSchemeBuilder(addKnownTypes, addDefaultingFuncs, addConversionFuncs, addFastPathConversionFuncs)
    AddToScheme   = SchemeBuilder.AddToScheme
)

这里可以看到v1相比较internal版本，还多了好几个函数addConversionFuncs, addFastPathConversionFuncs。
这些函数在执行AddToScheme()时其实都会要遍历执行，可以深入看下。其实就是向Scheme添加了转换函数，比如将v1.Pod转换为internal.Pod，将internal.Pod转换为v1.Pod。如果同时有v1,v2,v3会如何进行转换？其实也还是先统一转换成internal，然后再转换为相应的版本(v1,v2,v3).所以internal相当于转换的桥梁，更好的支持了不同版本的api。

到这里Scheme的初始化基本结束了。 上面讲GroupMeta初始化时还引出了关键性的RESTMapper，所以继续进行介绍。

该部分的初始化就直接看GroupMeta初始化时调用的接口newRESTMapper():
路径： pkg/api/install/install.go

func newRESTMapper(externalVersions []unversioned.GroupVersion) meta.RESTMapper {
    // 这些是API最顶层的对象，可以理解为没有namespace的对象
    // 根据有无namespace，对象分为两类：RESTScopeNamespace和RESTScopeRoot
    rootScoped := sets.NewString(
        "Node",
        "Namespace",
        "PersistentVolume",
        "ComponentStatus",
    )

    // 需要忽略Scheme中如下的kinds
    ignoredKinds := sets.NewString(
        "ListOptions",
        "DeleteOptions",
        "Status",
        "PodLogOptions",
        "PodExecOptions",
        "PodAttachOptions",
        "PodProxyOptions",
        "NodeProxyOptions",
        "ServiceProxyOptions",
        "ThirdPartyResource",
        "ThirdPartyResourceData",
        "ThirdPartyResourceList")

    mapper := api.NewDefaultRESTMapper(externalVersions, interfacesFor, importPrefix, ignoredKinds, rootScoped)

    return mapper
}

其实所有的api资源可以分为两类：一类是有namespace，另一类是没有namespace。比如该接口中的Node、Namespace、PersistentVolume、ComponentStatus不属于任何namespace。ignoredKinds是下面接口需要用到的参数，表示遍历Scheme时忽略这些kinds。
然后调用api.NewDefaultRESTMapper()，importPrefix参数为："k8s.io/kubernetes/pkg/api"，
interfacesFor是一个接口。
路径：pkg/api/mapper.go

func NewDefaultRESTMapper(defaultGroupVersions []unversioned.GroupVersion, interfacesFunc meta.VersionInterfacesFunc,
    importPathPrefix string, ignoredKinds, rootScoped sets.String) *meta.DefaultRESTMapper {
    // 加入Scheme,并继续调用下面的接口
    return NewDefaultRESTMapperFromScheme(defaultGroupVersions, interfacesFunc, importPathPrefix, ignoredKinds, rootScoped, Scheme)
}

func NewDefaultRESTMapperFromScheme(defaultGroupVersions []unversioned.GroupVersion, interfacesFunc meta.VersionInterfacesFunc,
    importPathPrefix string, ignoredKinds, rootScoped sets.String, scheme *runtime.Scheme) *meta.DefaultRESTMapper {
    // 初始化了一个DefaultRESTMapper对象
    mapper := meta.NewDefaultRESTMapper(defaultGroupVersions, interfacesFunc)
    // 根据输入的defaultGroupVersions,比如"/api/v1"，从Scheme中遍历所有的kinds
    // 然后进行Add
    for _, gv := range defaultGroupVersions {
        for kind, oType := range scheme.KnownTypes(gv) {
            gvk := gv.WithKind(kind)
            // 过滤掉不属于"k8s.io/kubernetes/pkg/api"路径下的api，和ignoredKinds
            if !strings.Contains(oType.PkgPath(), importPathPrefix) || ignoredKinds.Has(kind) {
                continue
            }
            // 判断该kind是否有namespace属性
            scope := meta.RESTScopeNamespace
            if rootScoped.Has(kind) {
                scope = meta.RESTScopeRoot
            }
            // 然后将该gvk加入到对应的组中
            mapper.Add(gvk, scope)
        }
    }
    return mapper
}

再看看该接口，先创建了一个空的DefaultRESTMapper,然后根据"/api/v1"的groupVersion,遍历Scheme中所有的kinds，接着再调用mapper.Add(gvk, scope)去填充这个mapper，最后返回该mapper。
看下mapper.Add()的实现：

func (m *DefaultRESTMapper) Add(kind unversioned.GroupVersionKind, scope RESTScope) {
    // resource还分为单数和复数
    plural, singular := KindToResource(kind)

    // 单数，复数相互转换
    m.singularToPlural[singular] = plural
    m.pluralToSingular[plural] = singular
    // 根据单复数的resource找到对应的kind
    m.resourceToKind[singular] = kind
    m.resourceToKind[plural] = kind
    // 根据kind找到对应的单复数resource
    m.kindToPluralResource[kind] = plural
    // kind到scope的转换
    m.kindToScope[kind] = scope
}

RESTMapper其实包含的是一种转换关系，resource到kind，kind到resource，kind到scope的转换。resource还分单数和复数。
kind和resource有什么区别呢？二者都是字符串，kind是通过Kind=reflector.TypeOf(&Pod{}).Elem().Name()进行取值，去的就是Pod这个结构体的名字。resource是通过plural, singular := KindToResource(kind)取值。singular是将Kind转换为小写字母，而plural是变为复数。
示例：以Pod为例，Kind是{Group:"", Version: "v1", Kind: "Pod"},那么singular是{Group:"", Version: "v1", Kind: "pod"},plural则是{Group："", Version："v1", Resource:"pods"}。
resource要区分单复数，是为了获取Pods信息。比如可以kubectl get pod，也可以kubectl get pods.

到这里RESTMapper也基本初始化完了，综合上面所有的初始化可以看到，其实主要用internal version和external versions填充Scheme，用external versions去填充GroupMeta以及其成员RESTMapper。
GroupMeta有啥作用呢？主要用于初始化APIGroupVersion。

之前所有的初始化都是为了这步做铺垫，上面还有一个APIGroupInfo和APIGroupVersion都没有进行介绍，这一节都会出现。
当API资源初始化完成以后，需要将这些API资源注册为restful api，用来接收用户的请求。
kube-apiServer使用了go-restful这套框架，里面主要包括三种对象：

Container: 一个Container包含多个WebService

WebService: 一个WebService包含多条route

Route: 一条route包含一个method(GET、POST、DELETE等)，一条具体的path(URL)以及一个响应的handler function。

API注册的入口函数有两个： m.InstallAPIs 和 m.InstallLegacyAPI。
文件路径：pkg/master/master.go
这两个函数分别用于注册"/api"和"/apis"的API,这里先拿InstallLegacyAPI进行介绍。
这些接口都是在config.Complete().New()函数中被调用：

    restOptionsFactory := restOptionsFactory{
        deleteCollectionWorkers: c.DeleteCollectionWorkers,
        enableGarbageCollection: c.GenericConfig.EnableGarbageCollection,
        storageFactory:          c.StorageFactory,
    }
    // 判断是否使能了用于Watch的Cache
    // 有无cache赋值的是不同的接口实现
    // restOptionsFactory.storageDecorator：是一个各个资源的REST interface(CRUD)装饰者
    // 后面调用NewStorage()时会用到该接口，并输出对应的CRUD接口及销毁接口。
    // 可以参考pkg/registry/core/pod/etcd/etcd.go中的NewStorage()
    // 其实这里有无cache的接口差异就在于：有cache的话，就提供操作cache的接口；无cache的话，就提供直接操作etcd的接口
    if c.EnableWatchCache {
        restOptionsFactory.storageDecorator = registry.StorageWithCacher
    } else {
        restOptionsFactory.storageDecorator = generic.UndecoratedStorage
    }

    // 判断/api/v1的group是否已经注册并enable，是的话再进行install
    if c.GenericConfig.APIResourceConfigSource.AnyResourcesForVersionEnabled(apiv1.SchemeGroupVersion) {
        // 该对象主要提供了一个NewLegacyRESTStorage()的接口
        legacyRESTStorageProvider := corerest.LegacyRESTStorageProvider{
            StorageFactory:       c.StorageFactory,
            ProxyTransport:       c.ProxyTransport,
            KubeletClientConfig:  c.KubeletClientConfig,
            EventTTL:             c.EventTTL,
            ServiceIPRange:       c.ServiceIPRange,
            ServiceNodePortRange: c.ServiceNodePortRange,
            LoopbackClientConfig: c.GenericConfig.LoopbackClientConfig,
        }
        // 进行"/api/v1"的API安装
        m.InstallLegacyAPI(c.Config, restOptionsFactory.NewFor, legacyRESTStorageProvider)
    }

继续查看m.InstallLegacyAPI()：

func (m *Master) InstallLegacyAPI(c *Config, restOptionsGetter genericapiserver.RESTOptionsGetter, legacyRESTStorageProvider corerest.LegacyRESTStorageProvider) {
    // 该对象前面介绍过了，比较关键，需要深入查看
    // 返回了RESTStorage和apiGroupInfo，都是重量级的成员
    // 这些初始化也就在这个接口中
    legacyRESTStorage, apiGroupInfo, err := legacyRESTStorageProvider.NewLegacyRESTStorage(restOptionsGetter)
    if err != nil {
        glog.Fatalf("Error building core storage: %v", err)
    }
    // 判断是否enable了controller,默认是true，这里跟主题关系不大，暂不深入
    if c.EnableCoreControllers {
        serviceClient := coreclient.NewForConfigOrDie(c.GenericConfig.LoopbackClientConfig)
        bootstrapController := c.NewBootstrapController(legacyRESTStorage, serviceClient)
        if err := m.GenericAPIServer.AddPostStartHook("bootstrap-controller", bootstrapController.PostStartHook); err != nil {
            glog.Fatalf("Error registering PostStartHook %q: %v", "bootstrap-controller", err)
        }
    }
    // install core Group"s API
    if err := m.GenericAPIServer.InstallLegacyAPIGroup(genericapiserver.DefaultLegacyAPIPrefix, &apiGroupInfo); err != nil {
        glog.Fatalf("Error in registering group versions: %v", err)
    }
}

先看下创建APIGroupVersion和RESTStorage对象的接口NewLegacyRESTStorage().
路径：pkg/registry/core/rest/storage_core.go

func (c LegacyRESTStorageProvider) NewLegacyRESTStorage(restOptionsGetter genericapiserver.RESTOptionsGetter) (LegacyRESTStorage, genericapiserver.APIGroupInfo, error) {
    // 初始化创建一个APIGroupVersion
    apiGroupInfo := genericapiserver.APIGroupInfo{
        // 该GroupMeta是从APIRegistrationManager初始化后的结构体获取
        GroupMeta:                    *registered.GroupOrDie(api.GroupName),
        VersionedResourcesStorageMap: map[string]map[string]rest.Storage{},
        // 这个api.Scheme之前已经介绍过其初始化了
        Scheme:                      api.Scheme,
        ParameterCodec:              api.ParameterCodec,
        NegotiatedSerializer:        api.Codecs,
        SubresourceGroupVersionKind: map[string]unversioned.GroupVersionKind{},
    }
    // 判断下autoscaling是否已经注册并使能，是的话加入到apiGroupInfo.SubresourceGroupVersionKind
    // key是该资源的path
    if autoscalingGroupVersion := (unversioned.GroupVersion{Group: "autoscaling", Version: "v1"}); registered.IsEnabledVersion(autoscalingGroupVersion) {
        apiGroupInfo.SubresourceGroupVersionKind["replicationcontrollers/scale"] = autoscalingGroupVersion.WithKind("Scale")
    }

    var podDisruptionClient policyclient.PodDisruptionBudgetsGetter
    if policyGroupVersion := (unversioned.GroupVersion{Group: "policy", Version: "v1beta1"}); registered.IsEnabledVersion(policyGroupVersion) {
        apiGroupInfo.SubresourceGroupVersionKind["pods/eviction"] = policyGroupVersion.WithKind("Eviction")

        var err error
        podDisruptionClient, err = policyclient.NewForConfig(c.LoopbackClientConfig)
        if err != nil {
            return LegacyRESTStorage{}, genericapiserver.APIGroupInfo{}, err
        }
    }
    // 初始化一个LegacyRESTStorage对象
    // 下面会进行各个接口的初始化，会有Node注册，IP申请，NodePort申请等等
    restStorage := LegacyRESTStorage{}
    // 创建各类Storage
    podTemplateStorage := podtemplateetcd.NewREST(restOptionsGetter(api.Resource("podTemplates")))

    eventStorage := eventetcd.NewREST(restOptionsGetter(api.Resource("events")), uint64(c.EventTTL.Seconds()))
    limitRangeStorage := limitrangeetcd.NewREST(restOptionsGetter(api.Resource("limitRanges")))

    resourceQuotaStorage, resourceQuotaStatusStorage := resourcequotaetcd.NewREST(restOptionsGetter(api.Resource("resourceQuotas")))
    secretStorage := secretetcd.NewREST(restOptionsGetter(api.Resource("secrets")))
    serviceAccountStorage := serviceaccountetcd.NewREST(restOptionsGetter(api.Resource("serviceAccounts")))
    persistentVolumeStorage, persistentVolumeStatusStorage := pvetcd.NewREST(restOptionsGetter(api.Resource("persistentVolumes")))
    persistentVolumeClaimStorage, persistentVolumeClaimStatusStorage := pvcetcd.NewREST(restOptionsGetter(api.Resource("persistentVolumeClaims")))
    configMapStorage := configmapetcd.NewREST(restOptionsGetter(api.Resource("configMaps")))

    namespaceStorage, namespaceStatusStorage, namespaceFinalizeStorage := namespaceetcd.NewREST(restOptionsGetter(api.Resource("namespaces")))
    restStorage.NamespaceRegistry = namespace.NewRegistry(namespaceStorage)

    endpointsStorage := endpointsetcd.NewREST(restOptionsGetter(api.Resource("endpoints")))
    restStorage.EndpointRegistry = endpoint.NewRegistry(endpointsStorage)

    nodeStorage, err := nodeetcd.NewStorage(restOptionsGetter(api.Resource("nodes")), c.KubeletClientConfig, c.ProxyTransport)
    if err != nil {
        return LegacyRESTStorage{}, genericapiserver.APIGroupInfo{}, err
    }
    restStorage.NodeRegistry = node.NewRegistry(nodeStorage.Node)

    // 创建PodStorage
    // api.Resource("pods")是合成了一个GroupResource的结构
    podStorage := podetcd.NewStorage(
        restOptionsGetter(api.Resource("pods")),
        nodeStorage.KubeletConnectionInfo,
        c.ProxyTransport,
        podDisruptionClient,
    )

    serviceRESTStorage, serviceStatusStorage := serviceetcd.NewREST(restOptionsGetter(api.Resource("services")))
    restStorage.ServiceRegistry = service.NewRegistry(serviceRESTStorage)

    var serviceClusterIPRegistry rangeallocation.RangeRegistry
    serviceClusterIPRange := c.ServiceIPRange
    if serviceClusterIPRange.IP == nil {
        return LegacyRESTStorage{}, genericapiserver.APIGroupInfo{}, fmt.Errorf("service clusterIPRange is missing")
    }

    serviceStorageConfig, err := c.StorageFactory.NewConfig(api.Resource("services"))
    if err != nil {
        return LegacyRESTStorage{}, genericapiserver.APIGroupInfo{}, err
    }

    ServiceClusterIPAllocator := ipallocator.NewAllocatorCIDRRange(&serviceClusterIPRange, func(max int, rangeSpec string) allocator.Interface {
        mem := allocator.NewAllocationMap(max, rangeSpec)
        // TODO etcdallocator package to return a storage interface via the storageFactory
        etcd := etcdallocator.NewEtcd(mem, "/ranges/serviceips", api.Resource("serviceipallocations"), serviceStorageConfig)
        serviceClusterIPRegistry = etcd
        return etcd
    })
    restStorage.ServiceClusterIPAllocator = serviceClusterIPRegistry

    var serviceNodePortRegistry rangeallocation.RangeRegistry
    ServiceNodePortAllocator := portallocator.NewPortAllocatorCustom(c.ServiceNodePortRange, func(max int, rangeSpec string) allocator.Interface {
        mem := allocator.NewAllocationMap(max, rangeSpec)
        // TODO etcdallocator package to return a storage interface via the storageFactory
        etcd := etcdallocator.NewEtcd(mem, "/ranges/servicenodeports", api.Resource("servicenodeportallocations"), serviceStorageConfig)
        serviceNodePortRegistry = etcd
        return etcd
    })
    restStorage.ServiceNodePortAllocator = serviceNodePortRegistry

    controllerStorage := controlleretcd.NewStorage(restOptionsGetter(api.Resource("replicationControllers")))

    serviceRest := service.NewStorage(restStorage.ServiceRegistry, restStorage.EndpointRegistry, ServiceClusterIPAllocator, ServiceNodePortAllocator, c.ProxyTransport)

    // 初始化了一个restStorage的map，然后赋值给APIGroupInfo.VersionedResourcesStorageMap["v1"]
    restStorageMap := map[string]rest.Storage{
        "pods":             podStorage.Pod,
        "pods/attach":      podStorage.Attach,
        "pods/status":      podStorage.Status,
        "pods/log":         podStorage.Log,
        "pods/exec":        podStorage.Exec,
        "pods/portforward": podStorage.PortForward,
        "pods/proxy":       podStorage.Proxy,
        "pods/binding":     podStorage.Binding,
        "bindings":         podStorage.Binding,

        "podTemplates": podTemplateStorage,

        "replicationControllers":        controllerStorage.Controller,
        "replicationControllers/status": controllerStorage.Status,

        "services":        serviceRest.Service,
        "services/proxy":  serviceRest.Proxy,
        "services/status": serviceStatusStorage,

        "endpoints": endpointsStorage,

        "nodes":        nodeStorage.Node,
        "nodes/status": nodeStorage.Status,
        "nodes/proxy":  nodeStorage.Proxy,

        "events": eventStorage,

        "limitRanges":                   limitRangeStorage,
        "resourceQuotas":                resourceQuotaStorage,
        "resourceQuotas/status":         resourceQuotaStatusStorage,
        "namespaces":                    namespaceStorage,
        "namespaces/status":             namespaceStatusStorage,
        "namespaces/finalize":           namespaceFinalizeStorage,
        "secrets":                       secretStorage,
        "serviceAccounts":               serviceAccountStorage,
        "persistentVolumes":             persistentVolumeStorage,
        "persistentVolumes/status":      persistentVolumeStatusStorage,
        "persistentVolumeClaims":        persistentVolumeClaimStorage,
        "persistentVolumeClaims/status": persistentVolumeClaimStatusStorage,
        "configMaps":                    configMapStorage,

        "componentStatuses": componentstatus.NewStorage(componentStatusStorage{c.StorageFactory}.serversToValidate),
    }
    if registered.IsEnabledVersion(unversioned.GroupVersion{Group: "autoscaling", Version: "v1"}) {
        restStorageMap["replicationControllers/scale"] = controllerStorage.Scale
    }
    if registered.IsEnabledVersion(unversioned.GroupVersion{Group: "policy", Version: "v1beta1"}) {
        restStorageMap["pods/eviction"] = podStorage.Eviction
    }
    // 将上面的restStorageMap赋值给v1
    apiGroupInfo.VersionedResourcesStorageMap["v1"] = restStorageMap

    return restStorage, apiGroupInfo, nil
}

看完这个接口后，我们继续回到前面，看下m.GenericAPIServer.InstallLegacyAPIGroup()接口：
路径：pkg/genericapiserver/genericapiserver.go

func (s *GenericAPIServer) InstallLegacyAPIGroup(apiPrefix string, apiGroupInfo *APIGroupInfo) error {
    // 判断前缀参数是否正确
    if !s.legacyAPIGroupPrefixes.Has(apiPrefix) {
        return fmt.Errorf("%q is not in the allowed legacy API prefixes: %v", apiPrefix, s.legacyAPIGroupPrefixes.List())
    }
    // 关键接口，真正install API
    if err := s.installAPIResources(apiPrefix, apiGroupInfo); err != nil {
        return err
    }

    // 获取了该Group下所有的version信息
    // 应该用于发现当前的所有版本信息
    apiVersions := []string{}
    for _, groupVersion := range apiGroupInfo.GroupMeta.GroupVersions {
        apiVersions = append(apiVersions, groupVersion.Version)
    }
    // Install the version handler.
    // Add a handler at / to enumerate the supported api versions.
    apiserver.AddApiWebService(s.Serializer, s.HandlerContainer.Container, apiPrefix, func(req *restful.Request) *unversioned.APIVersions {
        clientIP := utilnet.GetClientIP(req.Request)

        apiVersionsForDiscovery := unversioned.APIVersions{
            ServerAddressByClientCIDRs: s.discoveryAddresses.ServerAddressByClientCIDRs(clientIP),
            Versions:                   apiVersions,
        }
        return &apiVersionsForDiscovery
    })
    return nil
}

那我们继续进入关键接口s.installAPIResources(apiPrefix, apiGroupInfo):

func (s *GenericAPIServer) installAPIResources(apiPrefix string, apiGroupInfo *APIGroupInfo) error {
    // 遍历该Group下的所有GroupVersons
    for _, groupVersion := range apiGroupInfo.GroupMeta.GroupVersions {
        // 创建APIGroupVersion
        apiGroupVersion, err := s.getAPIGroupVersion(apiGroupInfo, groupVersion, apiPrefix)
        if err != nil {
            return err
        }
        if apiGroupInfo.OptionsExternalVersion != nil {
            apiGroupVersion.OptionsExternalVersion = apiGroupInfo.OptionsExternalVersion
        }
        // 根据之前创建的APIGroupVersion,然后安装restful API
        // 该s.HandlerContainer.Container就是go-restful的Container
        if err := apiGroupVersion.InstallREST(s.HandlerContainer.Container); err != nil {
            return fmt.Errorf("Unable to setup API %v: %v", apiGroupInfo, err)
        }
    }

    return nil
}

func (s *GenericAPIServer) getAPIGroupVersion(apiGroupInfo *APIGroupInfo, groupVersion unversioned.GroupVersion, apiPrefix string) (*apiserver.APIGroupVersion, error) {
    storage := make(map[string]rest.Storage)
    // 如果是核心组的话，Version为"v1",该VersionedResourcesStorageMap的初始化要看
    // 之前的NewLegacyRESTStorage()接口，在该接口中进行的初始化
    // 遍历所有的ResourcesStorage，并赋值给storage
    for k, v := range apiGroupInfo.VersionedResourcesStorageMap[groupVersion.Version] {
        storage[strings.ToLower(k)] = v
    }
    // 创建APIGroupVersion
    version, err := s.newAPIGroupVersion(apiGroupInfo, groupVersion)
    // 设置Prefix, 核心组的话是"/api"
    version.Root = apiPrefix
    version.Storage = storage
    return version, err
}

到这里从API资源到restful API,就已经注册完成了。
至于apiGroupVersion.InstallREST()接口，我们这里先简单介绍，后面会另起一篇文章结合go-restful进行介绍。
InstallREST()接口路径：pkg/apiserver/apiserver.go

func (g *APIGroupVersion) InstallREST(container *restful.Container) error {
    installer := g.newInstaller()
    ws := installer.NewWebService()
    apiResources, registrationErrors := installer.Install(ws)
    lister := g.ResourceLister
    if lister == nil {
        lister = staticLister{apiResources}
    }
    AddSupportedResourcesWebService(g.Serializer, ws, g.GroupVersion, lister)
    container.Add(ws)
    return utilerrors.NewAggregate(registrationErrors)
}

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,
    })

    // Register the paths in a deterministic (sorted) order to get a deterministic swagger spec.
    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 {
        // 该接口是关键，最终将一个rest.Storage对象转换成实际的restful api，比如getter、lister等处理函数，并将实际的URL关联起来
        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))
        }
        if apiResource != nil {
            apiResources = append(apiResources, *apiResource)
        }
    }
    return apiResources, errors
}

在这个注册的过程中，InstallREST最终调用了registerResourceHandlers()接口，该接口最终会把一个rest.Storage对象转换成实际的getter、lister等处理函数，并和实际的URL关联起来。

runtime-config： 用于enable/disable extensions group。默认的情况下DaemonSets、Deployments、HorizontalPodAutoscalers、Ingress、Jobs和ReplicaSets是使能的,还有v1下的默认都是使能的。另外的功能就可以通过该配置进行设置. 例如：disable deployments： --runtime-config=extensions/v1beta1/deployments=false.

1.api-group.md: https://github.com/kubernetes...