kubeAPIServer代码结构整理如下：
1. apiserver整体启动逻辑 k8s.io/kubernetes/cmd/kube-apiserver 2. apiserver bootstrap-controller创建&运行逻辑 k8s.io/kubernetes/pkg/master 3. API Resource对应后端RESTStorage(based on genericregistry.Store)创建k8s.io/kubernetes/pkg/registry 4. aggregated-apiserver创建&处理逻辑 k8s.io/kubernetes/staging/src/k8s.io/kube-aggregator 5. extensions-apiserver创建&处理逻辑 k8s.io/kubernetes/staging/src/k8s.io/apiextensions-apiserver 6. apiserver创建&运行 k8s.io/kubernetes/staging/src/k8s.io/apiserver/pkg/server 7. 注册API Resource资源处理handler(InstallREST&Install®isterResourceHandlers) k8s.io/kubernetes/staging/src/k8s.io/apiserver/pkg/endpoints 8. 创建存储后端(etcdv3) k8s.io/kubernetes/staging/src/k8s.io/apiserver/pkg/storage 9. genericregistry.Store.CompleteWithOptions初始化 k8s.io/kubernetes/staging/src/k8s.io/apiserver/pkg/registry调用链整理如下：
更多代码原理详情，参考 kubernetes-reading-notes 。
aggregatorServeraggregatorServer主要用于处理扩展Kubernetes API Resources的第二种方式Aggregated APIServer(AA)，将CR请求代理给AA：
这里结合Kubernetes官方给出的aggregated apiserver例子sample-apiserver，总结原理如下：
aggregatorServer通过APIServices对象关联到某个Service来进行请求的转发，其关联的Service类型进一步决定了请求转发的形式。aggregatorServer包括一个GenericAPIServer和维护自身状态的Controller。其中GenericAPIServer主要处理apiregistration.k8s.io组下的APIService资源请求，而Controller包括：
apiserviceRegistrationController：负责根据APIService定义的aggregated server service构建代理，将CR的请求转发给后端的aggregated server
availableConditionController：维护 APIServices 的可用状态，包括其引用 Service 是否可用等；
autoRegistrationController：用于保持 API 中存在的一组特定的 APIServices；
crdRegistrationController：负责将 CRD GroupVersions 自动注册到 APIServices 中；
openAPIAggregationController：将 APIServices 资源的变化同步至提供的 OpenAPI 文档；
apiserviceRegistrationController负责根据APIService定义的aggregated server service构建代理，将CR的请求转发给后端的aggregated server。apiService有两种类型：Local(Service为空)以及Service(Service非空)。apiserviceRegistrationController负责对这两种类型apiService设置代理：Local类型会直接路由给kube-apiserver进行处理；而Service类型则会设置代理并将请求转化为对aggregated Service的请求(proxyPath := "/apis/" + apiService.Spec.Group + "http://www.likecs.com/" + apiService.Spec.Version)，而请求的负载均衡策略则是优先本地访问kube-apiserver(如果service为kubernetes default apiserver service:443)=>通过service ClusterIP:Port访问(默认) 或者 通过随机选择service endpoint backend进行访问：
func (s *APIAggregator) AddAPIService(apiService *v1.APIService) error { ... proxyPath := "/apis/" + apiService.Spec.Group + "http://www.likecs.com/" + apiService.Spec.Version // v1. is a special case for the legacy API. It proxies to a wider set of endpoints. if apiService.Name == legacyAPIServiceName { proxyPath = "/api" } // register the proxy handler proxyHandler := &proxyHandler{ localDelegate: s.delegateHandler, proxyClientCert: s.proxyClientCert, proxyClientKey: s.proxyClientKey, proxyTransport: s.proxyTransport, serviceResolver: s.serviceResolver, egressSelector: s.egressSelector, } ... s.proxyHandlers[apiService.Name] = proxyHandler s.GenericAPIServer.Handler.NonGoRestfulMux.Handle(proxyPath, proxyHandler) s.GenericAPIServer.Handler.NonGoRestfulMux.UnlistedHandlePrefix(proxyPath+"http://www.likecs.com/", proxyHandler) ... // it's time to register the group aggregation endpoint groupPath := "/apis/" + apiService.Spec.Group groupDiscoveryHandler := &apiGroupHandler{ codecs: aggregatorscheme.Codecs, groupName: apiService.Spec.Group, lister: s.lister, delegate: s.delegateHandler, } // aggregation is protected s.GenericAPIServer.Handler.NonGoRestfulMux.Handle(groupPath, groupDiscoveryHandler) s.GenericAPIServer.Handler.NonGoRestfulMux.UnlistedHandle(groupPath+"http://www.likecs.com/", groupDiscoveryHandler) s.handledGroups.Insert(apiService.Spec.Group) return nil } // k8s.io/kubernetes/staging/src/k8s.io/kube-aggregator/pkg/apiserver/handler_proxy.go:109 func (r *proxyHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) { // 加载roxyHandlingInfo处理请求 value := r.handlingInfo.Load() if value == nil { r.localDelegate.ServeHTTP(w, req) return } handlingInfo := value.(proxyHandlingInfo) ... // 判断APIService服务是否正常 if !handlingInfo.serviceAvailable { proxyError(w, req, "service unavailable", http.StatusServiceUnavailable) return } // 将原始请求转化为对APIService的请求 // write a new location based on the existing request pointed at the target service location := &url.URL{} location.Scheme = "https" rloc, err := r.serviceResolver.ResolveEndpoint(handlingInfo.serviceNamespace, handlingInfo.serviceName, handlingInfo.servicePort) if err != nil { klog.Errorf("error resolving %s/%s: %v", handlingInfo.serviceNamespace, handlingInfo.serviceName, err) proxyError(w, req, "service unavailable", http.StatusServiceUnavailable) return } location.Host = rloc.Host location.Path = req.URL.Path location.RawQuery = req.URL.Query().Encode() newReq, cancelFn := newRequestForProxy(location, req) defer cancelFn() ... proxyRoundTripper = transport.NewAuthProxyRoundTripper(user.GetName(), user.GetGroups(), user.GetExtra(), proxyRoundTripper) handler := proxy.NewUpgradeAwareHandler(location, proxyRoundTripper, true, upgrade, &responder{w: w}) handler.ServeHTTP(w, newReq) } $ kubectl get APIService NAME SERVICE AVAILABLE AGE ... v1.apps Local True 50d ... v1beta1.metrics.k8s.io kube-system/metrics-server True 50d ... # default APIServices $ kubectl get -o yaml APIService/v1.apps apiVersion: apiregistration.k8s.io/v1 kind: APIService metadata: labels: kube-aggregator.kubernetes.io/automanaged: onstart name: v1.apps selfLink: /apis/apiregistration.k8s.io/v1/apiservices/v1.apps spec: group: apps groupPriorityMinimum: 17800 version: v1 versionPriority: 15 status: conditions: - lastTransitionTime: "2020-10-20T10:39:48Z" message: Local APIServices are always available reason: Local status: "True" type: Available # aggregated server $ kubectl get -o yaml APIService/v1beta1.metrics.k8s.io apiVersion: apiregistration.k8s.io/v1 kind: APIService metadata: labels: addonmanager.kubernetes.io/mode: Reconcile kubernetes.io/cluster-service: "true" name: v1beta1.metrics.k8s.io selfLink: /apis/apiregistration.k8s.io/v1/apiservices/v1beta1.metrics.k8s.io spec: group: metrics.k8s.io groupPriorityMinimum: 100 insecureSkipTLSVerify: true service: name: metrics-server namespace: kube-system port: 443 version: v1beta1 versionPriority: 100 status: conditions: - lastTransitionTime: "2020-12-05T00:50:48Z" message: all checks passed reason: Passed status: "True" type: Available # CRD $ kubectl get -o yaml APIService/v1.duyanghao.example.com apiVersion: apiregistration.k8s.io/v1 kind: APIService metadata: labels: kube-aggregator.kubernetes.io/automanaged: "true" name: v1.duyanghao.example.com selfLink: /apis/apiregistration.k8s.io/v1/apiservices/v1.duyanghao.example.com spec: group: duyanghao.example.com groupPriorityMinimum: 1000 version: v1 versionPriority: 100 status: conditions: - lastTransitionTime: "2020-12-11T08:45:37Z" message: Local APIServices are always available reason: Local status: "True" type: Available