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今天就跟大家聊聊有關Kubernetes APIServer的原理是什么，可能很多人都不太了解，為了讓大家更加了解，小編給大家總結了以下內容，希望大家根據這篇文章可以有所收獲。
整個Kubernetes技術體系由聲明式API以及Controller構成，而kube-apiserver是Kubernetes的聲明式api server，并為其它組件交互提供了橋梁。因此加深對kube-apiserver的理解就顯得至關重要了。
kube-apiserver作為整個Kubernetes集群操作etcd的唯一入口，負責Kubernetes各資源的認證&鑒權，校驗以及CRUD等操作，提供RESTful APIs，供其它組件調用：
kube-apiserver包含三種APIServer：
aggregatorServer：負責處理 apiregistration.k8s.io 組下的APIService資源請求，同時將來自用戶的請求攔截轉發給aggregated server(AA)
kubeAPIServer：負責對請求的一些通用處理，包括：認證、鑒權以及各個內建資源(pod, deployment，service and etc)的REST服務等
apiExtensionsServer：負責CustomResourceDefinition（CRD）apiResources以及apiVersions的注冊，同時處理CRD以及相應CustomResource（CR）的REST請求(如果對應CR不能被處理的話則會返回404)，也是apiserver Delegation的最后一環
另外還包括bootstrap-controller，主要負責Kubernetes default apiserver service的創建以及管理。
接下來將對上述組件進行概覽性總結。
apiserver bootstrap-controller創建&運行邏輯在k8s.io/kubernetes/pkg/master目錄
bootstrap-controller主要用于創建以及維護內部kubernetes default apiserver service
kubernetes default apiserver service spec.selector為空，這是default apiserver service與其它正常service的最大區別，表明了這個特殊的service對應的endpoints不由endpoints controller控制，而是直接受kube-apiserver bootstrap-controller管理(maintained by this code, not by the pod selector)
bootstrap-controller的幾個主要功能如下：
創建 default、kube-system 和 kube-public 以及 kube-node-lease 命名空間
創建&維護kubernetes default apiserver service以及對應的endpoint
提供基于Service ClusterIP的檢查及修復功能(--service-cluster-ip-range指定范圍)
提供基于Service NodePort的檢查及修復功能(--service-node-port-range指定范圍)
// k8s.io/kubernetes/pkg/master/controller.go:142
// Start begins the core controller loops that must exist for bootstrapping
// a cluster.
func (c *Controller) Start() {
if c.runner != nil {
return
}
// Reconcile during first run removing itself until server is ready.
endpointPorts := createEndpointPortSpec(c.PublicServicePort, "https", c.ExtraEndpointPorts)
if err := c.EndpointReconciler.RemoveEndpoints(kubernetesServiceName, c.PublicIP, endpointPorts); err != nil {
klog.Errorf("Unable to remove old endpoints from kubernetes service: %v", err)
}
repairClusterIPs := servicecontroller.NewRepair(c.ServiceClusterIPInterval, c.ServiceClient, c.EventClient, &c.ServiceClusterIPRange, c.ServiceClusterIPRegistry, &c.SecondaryServiceClusterIPRange, c.SecondaryServiceClusterIPRegistry)
repairNodePorts := portallocatorcontroller.NewRepair(c.ServiceNodePortInterval, c.ServiceClient, c.EventClient, c.ServiceNodePortRange, c.ServiceNodePortRegistry)
// run all of the controllers once prior to returning from Start.
if err := repairClusterIPs.RunOnce(); err != nil {
// If we fail to repair cluster IPs apiserver is useless. We should restart and retry.
klog.Fatalf("Unable to perform initial IP allocation check: %v", err)
}
if err := repairNodePorts.RunOnce(); err != nil {
// If we fail to repair node ports apiserver is useless. We should restart and retry.
klog.Fatalf("Unable to perform initial service nodePort check: %v", err)
}
// 定期執行bootstrap controller主要的四個功能(reconciliation)
c.runner = async.NewRunner(c.RunKubernetesNamespaces, c.RunKubernetesService, repairClusterIPs.RunUntil, repairNodePorts.RunUntil)
c.runner.Start()
}更多代碼原理詳情，參考 kubernetes-reading-notes 。
KubeAPIServer主要提供對內建API Resources的操作請求，為Kubernetes中各API Resources注冊路由信息，同時暴露RESTful API，使集群中以及集群外的服務都可以通過RESTful API操作Kubernetes中的資源
另外，kubeAPIServer是整個Kubernetes apiserver的核心，下面將要講述的aggregatorServer以及apiExtensionsServer都是建立在kubeAPIServer基礎上進行擴展的(補充了Kubernetes對用戶自定義資源的能力支持)
kubeAPIServer最核心的功能是為Kubernetes內置資源添加路由，如下：
調用 m.InstallLegacyAPI 將核心 API Resources添加到路由中，在apiserver中即是以 /api 開頭的 resource；
調用 m.InstallAPIs 將擴展的 API Resources添加到路由中，在apiserver中即是以 /apis 開頭的 resource；
// k8s.io/kubernetes/pkg/master/master.go:332
// New returns a new instance of Master from the given config.
// Certain config fields will be set to a default value if unset.
// Certain config fields must be specified, including:
// KubeletClientConfig
func (c completedConfig) New(delegationTarget genericapiserver.DelegationTarget) (*Master, error) {
...
// 安裝 LegacyAPI(core API)
// install legacy rest storage
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,
ServiceAccountMaxExpiration: c.ExtraConfig.ServiceAccountMaxExpiration,
APIAudiences: c.GenericConfig.Authentication.APIAudiences,
}
if err := m.InstallLegacyAPI(&c, c.GenericConfig.RESTOptionsGetter, legacyRESTStorageProvider); err != nil {
return nil, err
}
}
...
// 安裝 APIs(named groups apis)
if err := m.InstallAPIs(c.ExtraConfig.APIResourceConfigSource, c.GenericConfig.RESTOptionsGetter, restStorageProviders...); err != nil {
return nil, err
}
...
return m, nil
}整個kubeAPIServer提供了三類API Resource接口：
core group：主要在 /api/v1 下；
named groups：其 path 為 /apis/$GROUP/$VERSION；
系統狀態的一些 API：如/metrics 、/version 等；
而API的URL大致以 /apis/{group}/{version}/namespaces/{namespace}/resource/{name} 組成，結構如下圖所示：
kubeAPIServer會為每種API資源創建對應的RESTStorage，RESTStorage的目的是將每種資源的訪問路徑及其后端存儲的操作對應起來：通過構造的REST Storage實現的接口判斷該資源可以執行哪些操作（如：create、update等），將其對應的操作存入到action中，每一個操作對應一個標準的REST method，如create對應REST method為POST，而update對應REST method為PUT。最終根據actions數組依次遍歷，對每一個操作添加一個handler(handler對應REST Storage實現的相關接口)，并注冊到route，最終對外提供RESTful API，如下：
// m.GenericAPIServer.InstallLegacyAPIGroup --> s.installAPIResources --> apiGroupVersion.InstallREST --> installer.Install --> a.registerResourceHandlers
// k8s.io/kubernetes/staging/src/k8s.io/apiserver/pkg/endpoints/installer.go:181
func (a *APIInstaller) registerResourceHandlers(path string, storage rest.Storage, ws *restful.WebService) (*metav1.APIResource, error) {
...
// 1、判斷該 resource 實現了哪些 REST 操作接口，以此來判斷其支持的 verbs 以便為其添加路由
// what verbs are supported by the storage, used to know what verbs we support per path
creater, isCreater := storage.(rest.Creater)
namedCreater, isNamedCreater := storage.(rest.NamedCreater)
lister, isLister := storage.(rest.Lister)
getter, isGetter := storage.(rest.Getter)
...
// 2、為 resource 添加對應的 actions(+根據是否支持 namespace)
// Get the list of actions for the given scope.
switch {
case !namespaceScoped:
// Handle non-namespace scoped resources like nodes.
resourcePath := resource
resourceParams := params
itemPath := resourcePath + "/{name}"
nameParams := append(params, nameParam)
proxyParams := append(nameParams, pathParam)
...
// Handler for standard REST verbs (GET, PUT, POST and DELETE).
// Add actions at the resource path: /api/apiVersion/resource
actions = appendIf(actions, action{"LIST", resourcePath, resourceParams, namer, false}, isLister)
actions = appendIf(actions, action{"POST", resourcePath, resourceParams, namer, false}, isCreater)
...
}
...
// 3、從 rest.Storage 到 restful.Route 映射
// 為每個操作添加對應的 handler
for _, action := range actions {
...
switch action.Verb {
...
case "POST": // Create a resource.
var handler restful.RouteFunction
// 4、初始化 handler
if isNamedCreater {
handler = restfulCreateNamedResource(namedCreater, reqScope, admit)
} else {
handler = restfulCreateResource(creater, reqScope, admit)
}
handler = metrics.InstrumentRouteFunc(action.Verb, group, version, resource, subresource, requestScope, metrics.APIServerComponent, handler)
...
// 5、route 與 handler 進行綁定
route := ws.POST(action.Path).To(handler).
Doc(doc).
Param(ws.QueryParameter("pretty", "If 'true', then the output is pretty printed.")).
Operation("create"+namespaced+kind+strings.Title(subresource)+operationSuffix).
Produces(append(storageMeta.ProducesMIMETypes(action.Verb), mediaTypes...)...).
Returns(http.StatusOK, "OK", producedObject).
// TODO: in some cases, the API may return a v1.Status instead of the versioned object
// but currently go-restful can't handle multiple different objects being returned.
Returns(http.StatusCreated, "Created", producedObject).
Returns(http.StatusAccepted, "Accepted", producedObject).
Reads(defaultVersionedObject).
Writes(producedObject)
if err := AddObjectParams(ws, route, versionedCreateOptions); err != nil {
return nil, err
}
addParams(route, action.Params)
// 6、添加到路由中
routes = append(routes, route)
case "DELETE": // Delete a resource.
...
default:
return nil, fmt.Errorf("unrecognized action verb: %s", action.Verb)
}
for _, route := range routes {
route.Metadata(ROUTE_META_GVK, metav1.GroupVersionKind{
Group: reqScope.Kind.Group,
Version: reqScope.Kind.Version,
Kind: reqScope.Kind.Kind,
})
route.Metadata(ROUTE_META_ACTION, strings.ToLower(action.Verb))
ws.Route(route)
}
// Note: update GetAuthorizerAttributes() when adding a custom handler.
}
...
}kubeAPIServer代碼結構整理如下：
1. apiserver整體啟動邏輯 k8s.io/kubernetes/cmd/kube-apiserver 2. apiserver bootstrap-controller創建&運行邏輯 k8s.io/kubernetes/pkg/master 3. API Resource對應后端RESTStorage(based on genericregistry.Store)創建k8s.io/kubernetes/pkg/registry 4. aggregated-apiserver創建&處理邏輯 k8s.io/kubernetes/staging/src/k8s.io/kube-aggregator 5. extensions-apiserver創建&處理邏輯 k8s.io/kubernetes/staging/src/k8s.io/apiextensions-apiserver 6. apiserver創建&運行 k8s.io/kubernetes/staging/src/k8s.io/apiserver/pkg/server 7. 注冊API Resource資源處理handler(InstallREST&Install?isterResourceHandlers) k8s.io/kubernetes/staging/src/k8s.io/apiserver/pkg/endpoints 8. 創建存儲后端(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
調用鏈整理如下：
更多代碼原理詳情，參考 kubernetes-reading-notes 。
aggregatorServer主要用于處理擴展Kubernetes API Resources的第二種方式Aggregated APIServer(AA)，將CR請求代理給AA：
這里結合Kubernetes官方給出的aggregated apiserver例子sample-apiserver，總結原理如下：
aggregatorServer通過APIServices對象關聯到某個Service來進行請求的轉發，其關聯的Service類型進一步決定了請求轉發的形式。aggregatorServer包括一個GenericAPIServer和維護自身狀態的Controller。其中GenericAPIServer主要處理apiregistration.k8s.io組下的APIService資源請求，而Controller包括：
apiserviceRegistrationController：負責根據APIService定義的aggregated server service構建代理，將CR的請求轉發給后端的aggregated server
availableConditionController：維護 APIServices 的可用狀態，包括其引用 Service 是否可用等；
autoRegistrationController：用于保持 API 中存在的一組特定的 APIServices；
crdRegistrationController：負責將 CRD GroupVersions 自動注冊到 APIServices 中；
openAPIAggregationController：將 APIServices 資源的變化同步至提供的 OpenAPI 文檔；
apiserviceRegistrationController負責根據APIService定義的aggregated server service構建代理，將CR的請求轉發給后端的aggregated server。apiService有兩種類型：Local(Service為空)以及Service(Service非空)。apiserviceRegistrationController負責對這兩種類型apiService設置代理：Local類型會直接路由給kube-apiserver進行處理；而Service類型則會設置代理并將請求轉化為對aggregated Service的請求(proxyPath := "/apis/" + apiService.Spec.Group + "/" + apiService.Spec.Version)，而請求的負載均衡策略則是優先本地訪問kube-apiserver(如果service為kubernetes default apiserver service:443)=>通過service ClusterIP:Port訪問(默認) 或者 通過隨機選擇service endpoint backend進行訪問：
func (s *APIAggregator) AddAPIService(apiService *v1.APIService) error {
...
proxyPath := "/apis/" + apiService.Spec.Group + "/" + 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+"/", 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+"/", 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) {
// 加載roxyHandlingInfo處理請求
value := r.handlingInfo.Load()
if value == nil {
r.localDelegate.ServeHTTP(w, req)
return
}
handlingInfo := value.(proxyHandlingInfo)
...
// 判斷APIService服務是否正常
if !handlingInfo.serviceAvailable {
proxyError(w, req, "service unavailable", http.StatusServiceUnavailable)
return
}
// 將原始請求轉化為對APIService的請求
// 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
aggregatorServer創建過程中會根據所有kube-apiserver定義的API資源創建默認的APIService列表，名稱即是$VERSION.$GROUP，這些APIService都會有標簽kube-aggregator.kubernetes.io/automanaged: onstart，例如：v1.apps apiService。autoRegistrationController創建并維護這些列表中的APIService，也即我們看到的Local apiService；對于自定義的APIService(aggregated server)，則不會對其進行處理
aggregated server實現CR(自定義API資源) 的CRUD API接口，并可以靈活選擇后端存儲，可以與core kube-apiserver一起公用etcd，也可自己獨立部署etcd數據庫或者其它數據庫。aggregated server實現的CR API路徑為：/apis/$GROUP/$VERSION，具體到sample apiserver為：/apis/wardle.example.com/v1alpha1，下面的資源類型有：flunders以及fischers
aggregated server通過部署APIService類型資源，service fields指向對應的aggregated server service實現與core kube-apiserver的集成與交互
sample-apiserver目錄結構如下，可參考編寫自己的aggregated server：
staging/src/k8s.io/sample-apiserver ├── artifacts │ ├── example │ │ ├── apiservice.yaml ... ├── hack ├── main.go └── pkg ├── admission ├── apis ├── apiserver ├── cmd ├── generated │ ├── clientset │ │ └── versioned ... │ │ └── typed │ │ └── wardle │ │ ├── v1alpha1 │ │ └── v1beta1 │ ├── informers │ │ └── externalversions │ │ └── wardle │ │ ├── v1alpha1 │ │ └── v1beta1 │ ├── listers │ │ └── wardle │ │ ├── v1alpha1 │ │ └── v1beta1 └── registry
其中，artifacts用于部署yaml示例
hack目錄存放自動腳本(eg: update-codegen)
main.go是aggregated server啟動入口；pkg/cmd負責啟動aggregated server具體邏輯；pkg/apiserver用于aggregated server初始化以及路由注冊
pkg/apis負責相關CR的結構體定義，自動生成(update-codegen)
pkg/admission負責準入的相關代碼
pkg/generated負責生成訪問CR的clientset，informers，以及listers
pkg/registry目錄負責CR相關的RESTStorage實現
更多代碼原理詳情，參考 kubernetes-reading-notes 。
apiExtensionsServer主要負責CustomResourceDefinition（CRD）apiResources以及apiVersions的注冊，同時處理CRD以及相應CustomResource（CR）的REST請求(如果對應CR不能被處理的話則會返回404)，也是apiserver Delegation的最后一環
原理總結如下：
Custom Resource，簡稱CR，是Kubernetes自定義資源類型，與之相對應的就是Kubernetes內置的各種資源類型，例如Pod、Service等。利用CR我們可以定義任何想要的資源類型
CRD通過yaml文件的形式向Kubernetes注冊CR實現自定義api-resources，屬于第二種擴展Kubernetes API資源的方式，也是普遍使用的一種
APIExtensionServer負責CustomResourceDefinition（CRD）apiResources以及apiVersions的注冊，同時處理CRD以及相應CustomResource（CR）的REST請求(如果對應CR不能被處理的話則會返回404)，也是apiserver Delegation的最后一環
crdRegistrationController負責將CRD GroupVersions自動注冊到APIServices中。具體邏輯為：枚舉所有CRDs，然后根據CRD定義的crd.Spec.Group以及crd.Spec.Versions字段構建APIService，并添加到autoRegisterController.apiServicesToSync中，由autoRegisterController進行創建以及維護操作。這也是為什么創建完CRD后會產生對應的APIService對象
APIExtensionServer包含的controller以及功能如下所示：
- `namingController`：檢查 crd obj 中是否有命名沖突，可在 crd `.status.conditions` 中查看； - `establishingController`：檢查 crd 是否處于正常狀態，可在 crd `.status.conditions` 中查看； - `nonStructuralSchemaController`：檢查 crd obj 結構是否正常，可在 crd `.status.conditions` 中查看； - `apiApprovalController`：檢查 crd 是否遵循 Kubernetes API 聲明策略，可在 crd `.status.conditions` 中查看； - `finalizingController`：類似于 finalizes 的功能，與 CRs 的刪除有關；
openapiController：將 crd 資源的變化同步至提供的 OpenAPI 文檔，可通過訪問 /openapi/v2 進行查看；
crdController：負責將 crd 信息注冊到 apiVersions 和 apiResources 中，兩者的信息可通過 kubectl api-versions 和 kubectl api-resources 查看；
kubectl api-versions命令返回所有Kubernetes集群資源的版本信息（實際發出了兩個請求，分別是https://127.0.0.1:6443/api以及https://127.0.0.1:6443/apis，并在最后將兩個請求的返回結果進行了合并）
$ kubectl -v=8 api-versions
I1211 11:44:50.276446 22493 loader.go:375] Config loaded from file: /root/.kube/config
I1211 11:44:50.277005 22493 round_trippers.go:420] GET https://127.0.0.1:6443/api?timeout=32s
...
I1211 11:44:50.290265 22493 request.go:1068] Response Body: {"kind":"APIVersions","versions":["v1"],"serverAddressByClientCIDRs":[{"clientCIDR":"0.0.0.0/0","serverAddress":"x.x.x.x:6443"}]}
I1211 11:44:50.293673 22493 round_trippers.go:420] GET https://127.0.0.1:6443/apis?timeout=32s
...
I1211 11:44:50.298360 22493 request.go:1068] Response Body: {"kind":"APIGroupList","apiVersion":"v1","groups":[{"name":"apiregistration.k8s.io","versions":[{"groupVersion":"apiregistration.k8s.io/v1","version":"v1"},{"groupVersion":"apiregistration.k8s.io/v1beta1","version":"v1beta1"}],"preferredVersion":{"groupVersion":"apiregistration.k8s.io/v1","version":"v1"}},{"name":"extensions","versions":[{"groupVersion":"extensions/v1beta1","version":"v1beta1"}],"preferredVersion":{"groupVersion":"extensions/v1beta1","version":"v1beta1"}},{"name":"apps","versions":[{"groupVersion":"apps/v1","version":"v1"}],"preferredVersion":{"groupVersion":"apps/v1","version":"v1"}},{"name":"events.k8s.io","versions":[{"groupVersion":"events.k8s.io/v1beta1","version":"v1beta1"}],"preferredVersion":{"groupVersion":"events.k8s.io/v1beta1","version":"v1beta1"}},{"name":"authentication.k8s.io","versions":[{"groupVersion":"authentication.k8s.io/v1","version":"v1"},{"groupVersion":"authentication.k8s.io/v1beta1","version":"v1beta1"}],"preferredVersion":{"groupVersion":"authentication.k8s.io/v1"," [truncated 4985 chars]
apiextensions.k8s.io/v1
apiextensions.k8s.io/v1beta1
apiregistration.k8s.io/v1
apiregistration.k8s.io/v1beta1
apps/v1
authentication.k8s.io/v1beta1
...
storage.k8s.io/v1
storage.k8s.io/v1beta1
v1kubectl api-resources命令就是先獲取所有API版本信息，然后對每一個API版本調用接口獲取該版本下的所有API資源類型
$ kubectl -v=8 api-resources
5077 loader.go:375] Config loaded from file: /root/.kube/config
I1211 15:19:47.593450 15077 round_trippers.go:420] GET https://127.0.0.1:6443/api?timeout=32s
I1211 15:19:47.602273 15077 request.go:1068] Response Body: {"kind":"APIVersions","versions":["v1"],"serverAddressByClientCIDRs":[{"clientCIDR":"0.0.0.0/0","serverAddress":"x.x.x.x:6443"}]}
I1211 15:19:47.606279 15077 round_trippers.go:420] GET https://127.0.0.1:6443/apis?timeout=32s
I1211 15:19:47.610333 15077 request.go:1068] Response Body: {"kind":"APIGroupList","apiVersion":"v1","groups":[{"name":"apiregistration.k8s.io","versions":[{"groupVersion":"apiregistration.k8s.io/v1","version":"v1"},{"groupVersion":"apiregistration.k8s.io/v1beta1","version":"v1beta1"}],"preferredVersion":{"groupVersion":"apiregistration.k8s.io/v1","version":"v1"}},{"name":"extensions","versions":[{"groupVersion":"extensions/v1beta1","version":"v1beta1"}],"preferredVersion":{"groupVersion":"extensions/v1beta1","version":"v1beta1"}},{"name":"apps","versions":[{"groupVersion":"apps/v1","version":"v1"}],"preferredVersion":{"groupVersion":"apps/v1","version":"v1"}},{"name":"events.k8s.io","versions":[{"groupVersion":"events.k8s.io/v1beta1","version":"v1beta1"}],"preferredVersion":{"groupVersion":"events.k8s.io/v1beta1","version":"v1beta1"}},{"name":"authentication.k8s.io","versions":[{"groupVersion":"authentication.k8s.io/v1","version":"v1"},{"groupVersion":"authentication.k8s.io/v1beta1","version":"v1beta1"}],"preferredVersion":{"groupVersion":"authentication.k8s.io/v1"," [truncated 4985 chars]
I1211 15:19:47.614700 15077 round_trippers.go:420] GET https://127.0.0.1:6443/apis/batch/v1?timeout=32s
I1211 15:19:47.614804 15077 round_trippers.go:420] GET https://127.0.0.1:6443/apis/authentication.k8s.io/v1?timeout=32s
I1211 15:19:47.615687 15077 round_trippers.go:420] GET https://127.0.0.1:6443/apis/auth.tkestack.io/v1?timeout=32s
https://127.0.0.1:6443/apis/authentication.k8s.io/v1beta1?timeout=32s
I1211 15:19:47.616794 15077 round_trippers.go:420] GET https://127.0.0.1:6443/apis/coordination.k8s.io/v1?timeout=32s
I1211 15:19:47.616863 15077 round_trippers.go:420] GET https://127.0.0.1:6443/apis/apps/v1?timeout=32s
...
NAME SHORTNAMES APIGROUP NAMESPACED KIND
bindings true Binding
endpoints ep true Endpoints
events ev true Event
limitranges limits true LimitRange
namespaces ns false Namespace
nodes no false Node
...總結CR CRUD APIServer處理邏輯如下：
解析req(GET /apis/duyanghao.example.com/v1/namespaces/default/students)，根據請求路徑中的group(duyanghao.example.com)，version(v1)，以及resource字段(students)獲取對應CRD內容(crd, err := r.crdLister.Get(crdName))
通過crd.UID以及crd.Name獲取crdInfo，若不存在則創建對應的crdInfo(crdInfo, err := r.getOrCreateServingInfoFor(crd.UID, crd.Name))。crdInfo中包含了CRD定義以及該CRD對應Custom Resource的customresource.REST storage
customresource.REST storage由CR對應的Group(duyanghao.example.com)，Version(v1)，Kind(Student)，Resource(students)等創建完成，由于CR在Kubernetes代碼中并沒有具體結構體定義，所以這里會先初始化一個范型結構體Unstructured(用于保存所有類型的Custom Resource)，并對該結構體進行SetGroupVersionKind操作(設置具體Custom Resource Type)
從customresource.REST storage獲取Unstructured結構體后會對其進行相應轉換然后返回
// k8s.io/kubernetes/staging/src/k8s.io/apiextensions-apiserver/pkg/apiserver/customresource_handler.go:223
func (r *crdHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
ctx := req.Context()
requestInfo, ok := apirequest.RequestInfoFrom(ctx)
...
crdName := requestInfo.Resource + "." + requestInfo.APIGroup
crd, err := r.crdLister.Get(crdName)
...
crdInfo, err := r.getOrCreateServingInfoFor(crd.UID, crd.Name)
verb := strings.ToUpper(requestInfo.Verb)
resource := requestInfo.Resource
subresource := requestInfo.Subresource
scope := metrics.CleanScope(requestInfo)
...
switch {
case subresource == "status" && subresources != nil && subresources.Status != nil:
handlerFunc = r.serveStatus(w, req, requestInfo, crdInfo, terminating, supportedTypes)
case subresource == "scale" && subresources != nil && subresources.Scale != nil:
handlerFunc = r.serveScale(w, req, requestInfo, crdInfo, terminating, supportedTypes)
case len(subresource) == 0:
handlerFunc = r.serveResource(w, req, requestInfo, crdInfo, terminating, supportedTypes)
default:
responsewriters.ErrorNegotiated(
apierrors.NewNotFound(schema.GroupResource{Group: requestInfo.APIGroup, Resource: requestInfo.Resource}, requestInfo.Name),
Codecs, schema.GroupVersion{Group: requestInfo.APIGroup, Version: requestInfo.APIVersion}, w, req,
)
}
if handlerFunc != nil {
handlerFunc = metrics.InstrumentHandlerFunc(verb, requestInfo.APIGroup, requestInfo.APIVersion, resource, subresource, scope, metrics.APIServerComponent, handlerFunc)
handler := genericfilters.WithWaitGroup(handlerFunc, longRunningFilter, crdInfo.waitGroup)
handler.ServeHTTP(w, req)
return
}
}createAPIExtensionsServer=>NewCustomResourceDefinitionHandler=>crdHandler=>注冊CR CRUD API接口：
// New returns a new instance of CustomResourceDefinitions from the given config.
func (c completedConfig) New(delegationTarget genericapiserver.DelegationTarget) (*CustomResourceDefinitions, error) {
...
crdHandler, err := NewCustomResourceDefinitionHandler(
versionDiscoveryHandler,
groupDiscoveryHandler,
s.Informers.Apiextensions().V1().CustomResourceDefinitions(),
delegateHandler,
c.ExtraConfig.CRDRESTOptionsGetter,
c.GenericConfig.AdmissionControl,
establishingController,
c.ExtraConfig.ServiceResolver,
c.ExtraConfig.AuthResolverWrapper,
c.ExtraConfig.MasterCount,
s.GenericAPIServer.Authorizer,
c.GenericConfig.RequestTimeout,
time.Duration(c.GenericConfig.MinRequestTimeout)*time.Second,
apiGroupInfo.StaticOpenAPISpec,
c.GenericConfig.MaxRequestBodyBytes,
)
if err != nil {
return nil, err
}
s.GenericAPIServer.Handler.NonGoRestfulMux.Handle("/apis", crdHandler)
s.GenericAPIServer.Handler.NonGoRestfulMux.HandlePrefix("/apis/", crdHandler)
...
return s, nil
}本文從源碼層面對Kubernetes apiserver進行了一個概覽性總結，包括：aggregatorServer，kubeAPIServer，apiExtensionsServer以及bootstrap-controller等。
看完上述內容，你們對Kubernetes APIServer的原理是什么有進一步的了解嗎？如果還想了解更多知識或者相關內容，請關注億速云行業資訊頻道，感謝大家的支持。
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