apiserver源码分析——启动流程

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mob604757008d56 2021-10-04 15:59:00

文章标签 apiserver kubernetes k8s 实例化 ide 文章分类 代码人生

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()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