前言
apiserver是k8s控制面的一个组件，在众多组件中唯一一个对接etcd,对外暴露http服务的形式为k8s中各种资源提供增删改查等服务。它是RESTful风格，每个资源的URI都会形如
/apis/{apiGroup}/{version}/namsspaces/{ns-name}/{resource-kind}/{resource-name}
或
/apis/{apiGroup}/{version}/{resource-kind}/{resource-name}
apiserver中包含3个server组件，apiserver依靠这3个组件来对不同类型的请求提供处理
- APIExtensionServer: 主要负责处理CustomResourceDefination（CRD）方面的请求
- KubeAPIServer: 主要负责处理k8s内置资源的请求，此外还会包括通用处理，认证、鉴权等
- AggregratorServer: 主要负责aggregrate方面的处理，它充当一个代理服务器，将请求转发到聚合进来的k8s service中。
启动流程
本篇阅读源码版本1.19
apiserver同样使用了corbra命令行框架处理启动命令，它从命令行的RunE回调函数来到了Run函数，开始执行启动流程。Run函数做3件事
- 启动apiserver的3个server组件的路由
- 注册健康检查，就绪探针，存活探针的地址
- 启动http服务
代码位于 /cmd/kube-apiserver/app/server.go
func Run(completeOptions completedServerRunOptions, stopCh <-chan struct{}) error {
//注册三个server的路由
server, err := CreateServerChain(completeOptions, stopCh)
if err != nil {
return err
}
//注册健康检查，就绪，存活探针的地址
prepared, err := server.PrepareRun()
if err != nil {
return err
}
//运行http server
return prepared.Run(stopCh)
}
三个server的创建流程
CreateServerChain函数的调用如下
func CreateServerChain(...)(...){
kubeAPIServerConfig, insecureServingInfo, serviceResolver, pluginInitializer, err := CreateKubeAPIServerConfig(completedOptions, nodeTunneler, proxyTransport)
if err != nil {
return nil, err
}
// If additional API servers are added, they should be gated.
apiExtensionsConfig, err := createAPIExtensionsConfig(*kubeAPIServerConfig.GenericConfig, kubeAPIServerConfig.ExtraConfig.VersionedInformers, pluginInitializer, completedOptions.ServerRunOptions, completedOptions.MasterCount,
serviceResolver, webhook.NewDefaultAuthenticationInfoResolverWrapper(proxyTransport, kubeAPIServerConfig.GenericConfig.EgressSelector, kubeAPIServerConfig.GenericConfig.LoopbackClientConfig))
if err != nil {
return nil, err
}
//创建APIExtensionsServer并注册路由
apiExtensionsServer, err := createAPIExtensionsServer(apiExtensionsConfig, genericapiserver.NewEmptyDelegate())
if err != nil {
return nil, err
}
//创建KubeAPIServer并注册路由
kubeAPIServer, err := CreateKubeAPIServer(kubeAPIServerConfig, apiExtensionsServer.GenericAPIServer)
if err != nil {
return nil, err
}
// aggregator comes last in the chain
aggregatorConfig, err := createAggregatorConfig(*kubeAPIServerConfig.GenericConfig, completedOptions.ServerRunOptions, kubeAPIServerConfig.ExtraConfig.VersionedInformers, serviceResolver, proxyTransport, pluginInitializer)
if err != nil {
return nil, err
}
//创建aggregatorServer并注册路由
aggregatorServer, err := createAggregatorServer(aggregatorConfig, kubeAPIServer.GenericAPIServer, apiExtensionsServer.Informers)
if err != nil {
// we don't need special handling for innerStopCh because the aggregator server doesn't create any go routines
return nil, err
}
}
创建每个server都要有对应它的config。apiExtensionServer和aggregatorServer的Config需要依赖kubeAPIServerConfig，而这几个ServerConfig都需要依赖GenericConfig，CreateKubeAPIServerConfig创建kubeAPIServerConfig，而CreateKubeAPIServerConfig调用buildGenericConfig创建GenericConfig。
func buildGenericConfig(
s *options.ServerRunOptions,
proxyTransport *http.Transport,
)(...){
//创建一个genericConfig对象
genericConfig = genericapiserver.NewConfig(legacyscheme.Codecs)
//设置genericConfig的字段，代码不展示
//创建认证实例
if lastErr = s.Authentication.ApplyTo(&genericConfig.Authentication, genericConfig.SecureServing, genericConfig.EgressSelector, genericConfig.OpenAPIConfig, clientgoExternalClient, versionedInformers); lastErr != nil {
return
}
//创建鉴权实例
genericConfig.Authorization.Authorizer, genericConfig.RuleResolver, err = BuildAuthorizer(s, genericConfig.EgressSelector, versionedInformers)
//准入控制器
err = s.Admission.ApplyTo(
genericConfig,
versionedInformers,
kubeClientConfig,
feature.DefaultFeatureGate,
pluginInitializers...)
}
APIExtensionServer
APIExtensionServer的创建流程大致包含以下几个步骤
- 创建GeneriAPIServer
- 实例化CustomResourceDefinitions
- 实例化APIGroupInfo
- InstallAPIGroup
三种类型的Server底层都需要依赖GeneriAPIServer。第二步创建的CustomResourceDefinitions是本类型Server的对象，用于后续进行路由注册。APIGroupInfo是用于每个版本、每个资源类型对应的存储对象。最后调用InstallAPIGroup进行路由注册，把每一个资源的版本，类型映射到一个URI地址中。代码如下所示
func createAPIExtensionsServer(apiextensionsConfig *apiextensionsapiserver.Config, delegateAPIServer genericapiserver.DelegationTarget) (*apiextensionsapiserver.CustomResourceDefinitions, error) {
return apiextensionsConfig.Complete().New(delegateAPIServer)
}
//代码位于 /vendor/k8s.io/apiextensions-apiserver/apiserver.go
func (c completedConfig) New(delegationTarget genericapiserver.DelegationTarget) (*CustomResourceDefinitions, error) {
//创建Generic
genericServer, err := c.GenericConfig.New("apiextensions-apiserver", delegationTarget)
//实例化 CustomResourceDefinitions
s := &CustomResourceDefinitions{
GenericAPIServer: genericServer,
}
//实例化APIGroupInfo
apiGroupInfo := genericapiserver.NewDefaultAPIGroupInfo(apiextensions.GroupName, Scheme, metav1.ParameterCodec, Codecs)
if apiResourceConfig.VersionEnabled(v1beta1.SchemeGroupVersion) {
storage := map[string]rest.Storage{}
// customresourcedefinitions
customResourceDefinitionStorage, err := customresourcedefinition.NewREST(Scheme, c.GenericConfig.RESTOptionsGetter)
if err != nil {
return nil, err
}
storage["customresourcedefinitions"] = customResourceDefinitionStorage
storage["customresourcedefinitions/status"] = customresourcedefinition.NewStatusREST(Scheme, customResourceDefinitionStorage)
apiGroupInfo.VersionedResourcesStorageMap[v1beta1.SchemeGroupVersion.Version] = storage
}
//另一个版本的类似，不作展示
//InstallAPIGroup注册
if err := s.GenericAPIServer.InstallAPIGroup(&apiGroupInfo); err != nil {
return nil, err
}
}
KubeAPIServer
KubeAPIServer处理k8s内置资源请求，它的创建流程与APIExtensionServer类似，包含下面几个步骤
- 创建GeneriAPIServer
- 实例化Instance
- installLegacyAPI
- installAPI
其中Instance是KubeAPIServer的Server对象。KubeAPIServer创建和Install的APIGroup需要调用两个方法，一个是installLegacyAPI，另一个是installAPI，原因在于k8s的apiGroup分了/api和/apis两种。初期的资源其实没有apiGroup这个概念，而后期引入了groupVersion为了兼容原有的才把旧的资源类型的URI地址都归属于/api这个路径下的，新的全部在/apis这个路径下，因此在创建注册APIGroup时都分了两类。代码如下
func CreateKubeAPIServer(kubeAPIServerConfig *controlplane.Config, delegateAPIServer genericapiserver.DelegationTarget) (*controlplane.Instance, error) {
kubeAPIServer, err := kubeAPIServerConfig.Complete().New(delegateAPIServer)
if err != nil {
return nil, err
}
return kubeAPIServer, nil
}
//代码位于 /vendor/k8s.io/kube-aggregrator/pkg/apiserver/apiserver.go
func (c completedConfig) New(delegationTarget genericapiserver.DelegationTarget) (*Instance, error) {
//创建Generic
s, err := c.GenericConfig.New("kube-apiserver", delegationTarget)
//1.14版本的是Master,当前版本是Instance
m := &Instance{
GenericAPIServer: s,
ClusterAuthenticationInfo: c.ExtraConfig.ClusterAuthenticationInfo,
}
//实例化核心API
if c.ExtraConfig.APIResourceConfigSource.VersionEnabled(apiv1.SchemeGroupVersion) {
legacyRESTStorageProvider := corerest.LegacyRESTStorageProvider{
StorageFactory: c.ExtraConfig.StorageFactory,
ProxyTransport: c.ExtraConfig.ProxyTransport,
KubeletClientConfig: c.ExtraConfig.KubeletClientConfig,
EventTTL: c.ExtraConfig.EventTTL,
ServiceIPRange: c.ExtraConfig.ServiceIPRange,
SecondaryServiceIPRange: c.ExtraConfig.SecondaryServiceIPRange,
ServiceNodePortRange: c.ExtraConfig.ServiceNodePortRange,
LoopbackClientConfig: c.GenericConfig.LoopbackClientConfig,
ServiceAccountIssuer: c.ExtraConfig.ServiceAccountIssuer,
ExtendExpiration: c.ExtraConfig.ExtendExpiration,
ServiceAccountMaxExpiration: c.ExtraConfig.ServiceAccountMaxExpiration,
APIAudiences: c.GenericConfig.Authentication.APIAudiences,
}
if err := m.InstallLegacyAPI(&c, c.GenericConfig.RESTOptionsGetter, legacyRESTStorageProvider); err != nil {
return nil, err
}
}
restStorageProviders := []RESTStorageProvider{...}
//InstallAPIs，内部包含InstallAPIGroup
if err := m.InstallAPIs(c.ExtraConfig.APIResourceConfigSource, c.GenericConfig.RESTOptionsGetter, restStorageProviders...); err != nil {
return nil, err
}
}
注册核心apiGroups
进入m.InstallLegacyAPI,这个方法包含了实例化ApiGroupInfo和InstalAPIGroup两个操作，这部分资源是k8s的核心资源
func (m *Instance) InstallLegacyAPI(c *completedConfig, restOptionsGetter generic.RESTOptionsGetter, legacyRESTStorageProvider corerest.LegacyRESTStorageProvider) error {
//实例化ApiGroupInfo
legacyRESTStorage, apiGroupInfo, err := legacyRESTStorageProvider.NewLegacyRESTStorage(restOptionsGetter)
if err != nil {
return fmt.Errorf("error building core storage: %v", err)
}
controllerName := "bootstrap-controller"
coreClient := corev1client.NewForConfigOrDie(c.GenericConfig.LoopbackClientConfig)
bootstrapController := c.NewBootstrapController(legacyRESTStorage, coreClient, coreClient, coreClient, coreClient.RESTClient())
m.GenericAPIServer.AddPostStartHookOrDie(controllerName, bootstrapController.PostStartHook)
m.GenericAPIServer.AddPreShutdownHookOrDie(controllerName, bootstrapController.PreShutdownHook)
//相当于调用InstallAPIGroup
if err := m.GenericAPIServer.InstallLegacyAPIGroup(genericapiserver.DefaultLegacyAPIPrefix, &apiGroupInfo); err != nil {
return fmt.Errorf("error in registering group versions: %v", err)
}
return nil
}
实例化APIGroupInfo的代码局部如下，代码篇幅较长，只摘取pod一部分的源码展示，代码位于/pkg/registry/core/rest/storage_core.go
func (c LegacyRESTStorageProvider) NewLegacyRESTStorage(restOptionsGetter generic.RESTOptionsGetter) (LegacyRESTStorage, genericapiserver.APIGroupInfo, error) {
apiGroupInfo := genericapiserver.APIGroupInfo{
PrioritizedVersions: legacyscheme.Scheme.PrioritizedVersionsForGroup(""),
VersionedResourcesStorageMap: map[string]map[string]rest.Storage{},
Scheme: legacyscheme.Scheme,
ParameterCodec: legacyscheme.ParameterCodec,
NegotiatedSerializer: legacyscheme.Codecs,
}
podStorage, err := podstore.NewStorage(
restOptionsGetter,
nodeStorage.KubeletConnectionInfo,
c.ProxyTransport,
podDisruptionClient,
)
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.LegacyBinding,
.....
}
}
m.GenericAPIServer.InstallLegacyAPIGroup的第一个参数是apiPrefix，值是/api;第二个参数是上面创建好的，包含资源存储方式的apiGroupInfo
与InstallAPIGroup类似地，InstallLegacyAPIGroup需要经过两层调用才会到达InstallREST，调用链如下
m.GenericAPIServer.InstallLegacyAPIGroup
|--s.installAPIResources
|--apiGroupVersion.InstallREST
InstallREST的入参是restful.Container，他是golang http框架go-restful里面的一个重要对象，在InstallREST里面构造出installer，installer包含资源的存储方法和资源对应api的前缀，利用installer.Install()来创建出go-restful的webservice,webservice加入到传入得container，即完成api的注册。
代码位于/vendor/k8s.io/apiserver/pkg/endpoints/groupversion.go
func (g *APIGroupVersion) InstallREST(container *restful.Container) error {
prefix := path.Join(g.Root, g.GroupVersion.Group, g.GroupVersion.Version)
installer := &APIInstaller{
group: g,
prefix: prefix,
minRequestTimeout: g.MinRequestTimeout,
}
apiResources, ws, registrationErrors := installer.Install()
versionDiscoveryHandler := discovery.NewAPIVersionHandler(g.Serializer, g.GroupVersion, staticLister{apiResources})
versionDiscoveryHandler.AddToWebService(ws)
container.Add(ws)
return utilerrors.NewAggregate(registrationErrors)
}
installer.Install()创建了webservice，api中各个URL的路由注册，handler的绑定也会在里面实现。由于这部分代码也涉及到apiserver如何响应处理一个http请求，本篇先不探讨
go-restful框架
不过上面提及到go-restful框架的几个概念，在这里进行一个简单的科普
- container:在http的角度就是一个Server,里面就包含若干个webservice
- webservice:webservice从结构来说是承上启下的一个角色，它包含了一组route，而且这组route都会有一个共同的basePath或者说他们的URL的prefix是相同的
- route:route对应具体的一个URL,它需要指定具体的路径Path，请求方法Method和处理函数Handler，以及一些参数Parameter等等。
他们的层次结构如下
container
|--webservice
|--Route
AggregratorServer
用于处理聚合进来的api请求，实际是做七层转发，它的创建流程与APIExtensionServer的最为相似
- 创建GeneriAPIServer
- 实例化Aggregrator
- 实例化APIGroupInfo
- InstallAPIGroup
实际创建AggregratorServer的代码位于/vendor/k8s.io/kube-aggregrator/pkg/apiserver/apiserver.go
func (c completedConfig) NewWithDelegate(delegationTarget genericapiserver.DelegationTarget) (*APIAggregator, error) {
//创建GeneriAPIServer
genericServer, err := c.GenericConfig.New("kube-aggregator", delegationTarget)
//实例化Aggregrator
s := &APIAggregator{...}
//实例化APIGroupInfo
apiGroupInfo := apiservicerest.NewRESTStorage(c.GenericConfig.MergedResourceConfig, c.GenericConfig.RESTOptionsGetter)
//InstallAPIGroup
if err := s.GenericAPIServer.InstallAPIGroup(&apiGroupInfo); err != nil {
return nil, err
}
}
运行http server
api的路由绑定完毕，最后就是要把http server跑起来，prepared.Run调用的是由preparedGenericAPIServer实现的Run方法，经过多层调用最终把server跑起来，调用链如下
prepared.Run /vendor/k8s.io/kube-aggregrator/pkg/apiserver/apiserver.go
|--s.runnable.Run(stopCh)
|==preparedGenericAPIServer.Run /vendor/k8s.io/apiserver/pkg/server/genericapiserver.go
|--s.NonBlockingRun
|--s.SecureServingInfo.Serve /vendor/k8s.io/kube-aggregrator/pkg/server/secure_serving.go
|--&http.Server{}
|--RunServer
http server的对象是在SecureServingInfo.Serve创建的，即调用链的s.SecureServingInfo.Serve，最终让server开始监听是在RunServer处。它接收了http.Server作为参数。至此apiserver运行起来，接收来自各个组件或客户端的请求。
小结
本篇讲述了k8s-apiserver的启动流程，介绍了apiserver包含了3个server组件，apiserver的服务实际上由这三个组件提供，讲述了他们创建流程，实例化底层的GenericServer，实例化各自的Server类，实例化ApiGroupInfo来建立资源与存储操作间的映射关系，最后InstallAPI。还专门挑了k8s核心资源类型的ApiGroup注册过程介绍。整个启动过程的调用链如下
Run /cmd/kube-apiserver/app/server.go
|--CreateServerChain
| |--CreateKubeAPIServerConfig
| | |--buildGenericConfig
| | |--genericapiserver.NewConfig
| | |--s.Authentication.ApplyTo
| | |--BuildAuthorizer
| | |--s.Admission.ApplyTo
| |--createAPIExtensionsConfig
| |--createAPIExtensionsServer
| | |--apiextensionsConfig.Complete().New /vendor/k8s.io/apiextensions-apiserver/apiserver.go
| | |--c.GenericConfig.New
| | |--&CustomResourceDefinitions{}
| | |--genericapiserver.NewDefaultAPIGroupInfo
| | |--s.GenericAPIServer.InstallAPIGroup
| |--CreateKubeAPIServer
| | |--kubeAPIServerConfig.Complete().New /pkg/controlplane/instance.go
| | | |--c.GenericConfig.New
| | | |--&Instance{}
| | | |--m.InstallLegacyAPI /pkg/controlplane/instance.go
| | | | |--legacyRESTStorageProvider.NewLegacyRESTStorage /pkg/registry/core/rest/storage_core.go
| | | | |--m.GenericAPIServer.InstallLegacyAPIGroup ##相当于新版本的InstallAPIGroup
| | | | | |--s.installAPIResources
| | | | | | |--apiGroupVersion.InstallREST
| | | |--m.InstallAPIs
| |--createAggregatorConfig
| |--createAggregatorServer
| |--aggregatorConfig.Complete().NewWithDelegate /vendor/k8s.io/kube-aggregrator/pkg/apiserver/apiserver.go
| |--c.GenericConfig.New
| |--&APIAggregator{}
| |--apiservicerest.NewRESTStorage
| |--s.GenericAPIServer.InstallAPIGroup
|--server.PrepareRun /vendor/k8s.io/kube-aggregrator/pkg/apiserver/apiserver.go
| |--s.GenericAPIServer.PrepareRun /vendor/k8s.io/kube-aggregrator/pkg/server/genericapiserver.go
| |--s.installHealthz()
| |--s.installLivez()
| |--s.installReadyz()
|--prepared.Run /vendor/k8s.io/kube-aggregrator/pkg/apiserver/apiserver.go
|--s.runnable.Run(stopCh)
|==preparedGenericAPIServer.Run /vendor/k8s.io/apiserver/pkg/server/genericapiserver.go
|--s.NonBlockingRun
|--s.SecureServingInfo.Serve /vendor/k8s.io/kube-aggregrator/pkg/server/secure_serving.go
|--&http.Server{}
|--RunServer
如有兴趣,可阅读鄙人“k8s源码之旅”系列的其他文章
kubelet源码分析——kubelet简介与启动
kubelet源码分析——启动Pod
kubelet源码分析——关闭Pod
kubelet源码分析——监控Pod变更
scheduler源码分析——调度流程
apiserver源码分析——启动流程
apiserver源码分析——处理请求