K8s-apiserver工作原理

梦想与她 提交于 2021-02-02 15:32:10


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:

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

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

$ kubectl proxy --port=8080 &

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

curl

# 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)

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:
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:

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:

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:

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



END

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