apiserver源码分析——启动流程

2022-09-20 12:05:27

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

  1. 启动apiserver的3个server组件的路由
  2. 注册健康检查，就绪探针，存活探针的地址
  3. 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()方法的边幅很长，它既然创建了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
scheduler源码分析——调度流程
apiserver源码分析——启动流程

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