k8s-apiserver工作原理

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API Server

kube-apiserver 是 Kubernetes 最重要的核心组件之一，主要提供以下的功能

  • 提供集群管理的 REST API 接口，包括认证授权、数据校验以及集群状态变更等
  • 提供其他模块之间的数据交互和通信的枢纽（其他模块通过 API Server 查询或修改数据，只有 API Server 才直接操作 etcd）

工作原理

kube-apiserver 提供了 Kubernetes 的 REST API，实现了认证、授权、准入控制等安全校验功能，同时也负责集群状态的存储操作（通过 etcd）。

API 访问

有多种方式可以访问 Kubernetes 提供的 REST API：

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1、kubectl 命令行工具
2、SDK，支持多种语言
Go
Python
Javascript
Java
CSharp
3、其他 OpenAPI 支持的语言，可以通过 gen 工具生成相应的 client

kubectl

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kubectl get --raw /api/v1/namespaces
kubectl get --raw /apis/metrics.k8s.io/v1beta1/nodes
kubectl get --raw /apis/metrics.k8s.io/v1beta1/pods

kubectl proxy

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$ kubectl proxy --port=8080 &

$ curl http://localhost:8080/api/
{
  "versions": [
    "v1"
  ]
}

curl

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# In Pods with service account.
$ TOKEN=$(cat /run/secrets/kubernetes.io/serviceaccount/token)
$ CACERT=/run/secrets/kubernetes.io/serviceaccount/ca.crt
$ curl --cacert $CACERT --header "Authorization: Bearer $TOKEN"  https://$KUBERNETES_SERVICE_HOST:$KUBERNETES_SERVICE_PORT/api
{
  "kind": "APIVersions",
  "versions": [
    "v1"
  ],
  "serverAddressByClientCIDRs": [
    {
      "clientCIDR": "0.0.0.0/0",
      "serverAddress": "10.0.1.149:443"
    }
  ]
}
# Outside of Pods.
$ APISERVER=$(kubectl config view | grep server | cut -f 2- -d ":" | tr -d " ")
$ TOKEN=$(kubectl describe secret $(kubectl get secrets | grep default | cut -f1 -d ' ') | grep -E '^token'| cut -f2 -d':'| tr -d '\t')
$ curl $APISERVER/api --header "Authorization: Bearer $TOKEN" --insecure
{
  "kind": "APIVersions",
  "versions": [
    "v1"
  ],
  "serverAddressByClientCIDRs": [
    {
      "clientCIDR": "0.0.0.0/0",
      "serverAddress": "10.0.1.149:443"
    }
  ]
}

API 资源使用

API Resources

我们可以通过下面的命令来获取Kubernetes集群支持的所有 API 资源： （1.11以上版本才可以有此命令）

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kubectl api-resources -o wide
NAME                              SHORTNAMES   APIGROUP                       NAMESPACED   KIND                             VERBS
bindings                                                                      true         Binding                          [create]
componentstatuses                 cs                                          false        ComponentStatus                  [get list]
configmaps                        cm                                          true         ConfigMap                        [create delete deletecollection get list patch update watch]
endpoints                         ep                                          true         Endpoints                        [create delete deletecollection get list patch update watch]
events                            ev                                          true         Event                            [create delete deletecollection get list patch update watch]
limitranges                       limits                                      true         LimitRange                       [create delete deletecollection get list patch update watch]
namespaces                        ns                                          false        Namespace                        [create delete get list patch update watch]
nodes                             no                                          false        Node                             [create delete deletecollection get list patch proxy update watch]
persistentvolumeclaims            pvc                                         true         PersistentVolumeClaim            [create delete deletecollection get list patch update watch]
persistentvolumes                 pv                                          false        PersistentVolume                 [create delete deletecollection get list patch update watch]
pods                              po                                          true         Pod                              [create delete deletecollection get list patch proxy update watch]
podtemplates                                                                  true         PodTemplate                      [create delete deletecollection get list patch update watch]
replicationcontrollers            rc                                          true         ReplicationController            [create delete deletecollection get list patch update watch]
resourcequotas                    quota                                       true         ResourceQuota                    [create delete deletecollection get list patch update watch]
secrets                                                                       true         Secret                           [create delete deletecollection get list patch update watch]
serviceaccounts                   sa                                          true         ServiceAccount                   [create delete deletecollection get list patch update watch]
services                          svc                                         true         Service                          [create delete get list patch proxy update watch]
mutatingwebhookconfigurations                  admissionregistration.k8s.io   false        MutatingWebhookConfiguration     [create delete deletecollection get list patch update watch]
validatingwebhookconfigurations                admissionregistration.k8s.io   false        ValidatingWebhookConfiguration   [create delete deletecollection get list patch update watch]
customresourcedefinitions         crd          apiextensions.k8s.io           false        CustomResourceDefinition         [create delete deletecollection get list patch update watch]
apiservices                                    apiregistration.k8s.io         false        APIService                       [create delete deletecollection get list patch update watch]
controllerrevisions                            apps                           true         ControllerRevision               [create delete deletecollection get list patch update watch]
daemonsets                        ds           apps                           true         DaemonSet                        [create delete deletecollection get list patch update watch]
deployments                       deploy       apps                           true         Deployment                       [create delete deletecollection get list patch update watch]
replicasets                       rs           apps                           true         ReplicaSet                       [create delete deletecollection get list patch update watch]
statefulsets                      sts          apps                           true         StatefulSet                      [create delete deletecollection get list patch update watch]
...

上面的命令输出了很多有用的信息：

  • SHORTNAMES - 资源名称的简写，比如 deployments 简写就是 deploy，我们可以将这些快捷方式与kubectl一起使用
  • APIGROUP - 我们可以查看官方文档以了解更多信息，但简而言之，您将在yaml文件中使用它像apiVersion：<APIGROUP>/v1
  • KIND - 资源名称
  • VERBS - 可用的方法，在您想要定义ClusterRole RBAC规则时也很有用，您还可以选择获取特定 API 组的 API 资源，例如：
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kubectl api-resources --api-group apps -o wide
NAME                  SHORTNAMES   APIGROUP   NAMESPACED   KIND                 VERBS
controllerrevisions                apps       true         ControllerRevision   [create delete deletecollection get list patch update watch]
daemonsets            ds           apps       true         DaemonSet            [create delete deletecollection get list patch update watch]
deployments           deploy       apps       true         Deployment           [create delete deletecollection get list patch update watch]
replicasets           rs           apps       true         ReplicaSet           [create delete deletecollection get list patch update watch]
statefulsets          sts          apps       true         StatefulSet

对于上面的每种资源类型，我们都可以使用kubectl explain命令来获取有关的资源详细信息：

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kubectl explain configmap
DESCRIPTION:
ConfigMap holds configuration data for pods to consume.

FIELDS:
   apiVersion   <string>
     APIVersion defines the versioned schema of this representation of an
     object. Servers should convert recognized schemas to the latest internal
     value, and may reject unrecognized values. More info:
     https://git.k8s.io/community/contributors/devel/api-conventions.md#resources

   data <object>
     Data contains the configuration data. Each key must consist of alphanumeric
     characters, '-', '_' or '.'.

   kind <string>
     Kind is a string value representing the REST resource this object
     represents. Servers may infer this from the endpoint the client submits
     requests to. Cannot be updated. In CamelCase. More info:
     https://git.k8s.io/community/contributors/devel/api-conventions.md#types-kinds

   metadata <Object>
     Standard object's metadata. More info:
     https://git.k8s.io/community/contributors/devel/api-conventions.md#metadata

kubectl explain命令非常有用，特别是在我们不知道该如何编写YAML文件的时候，就可以使用改命令来帮助我们获得更多提示信息。

需要注意的是explain命令可能会显示旧的group/version，我们可以通过--api-version参数显示设置它，比如： 请注意，explain可能会显示旧组/版本，但您可以使用–api-version显式设置它，例如：

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kubectl explain replicaset --api-version apps/v1

API Versions

我们也可以使用下面的命令来获取集群支持的所有 API 版本：

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kubectl api-versions
admissionregistration.k8s.io/v1beta1
apiextensions.k8s.io/v1beta1
apiregistration.k8s.io/v1beta1
apps/v1
apps/v1beta1
apps/v1beta2
authentication.k8s.io/v1
authentication.k8s.io/v1beta1
authorization.k8s.io/v1
authorization.k8s.io/v1beta1
autoscaling/v1
autoscaling/v2beta1
batch/v1
batch/v1beta1
certificates.k8s.io/v1beta1
certmanager.k8s.io/v1alpha1
enterprises.upmc.com/v1
events.k8s.io/v1beta1
extensions/v1beta1
metrics.k8s.io/v1beta1
monitoring.coreos.com/v1
networking.k8s.io/v1
policy/v1beta1
rbac.authorization.k8s.io/v1
rbac.authorization.k8s.io/v1beta1
storage.k8s.io/v1
storage.k8s.io/v1beta1
v1
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