API Server and API Object

参考：

• https://kubernetes.io/docs/reference/using-api/

• https://kubernetes.io/docs/concepts/overview/working-with-objects/kubernetes-objects/

• https://kubernetes.io/docs/reference/kubernetes-api/

API Server

Kubernetes的API Server是一个client/server的架构

• 通过HTTP对外提供RESTful　API服务，client提交请求，server回复

• 是无状态的stateless，所有的状态都存储在cluster　store里（etcd）

$ kubectl cluster-info
$ kubectl config view
$ kubectl config view --raw
$ kubectl config get-contexts

Clients

• kubectl

• RESTful API

• other clients

API Object

API Object是通过API server可以操作的Kubernetes对象，它们代表了整个集群的状态，比如：

• What containerized applications are running (and on which nodes)

• The resources available to those applications

• The policies around how those applications behave, such as restart policies, upgrades, and fault-tolerance

API Object通过以下字段组织起来

• Kind (Pod, Deployment, Service, etc.)

• Group (core, apps, storage), see https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.26/

• Version (v1, beta, alpha) see https://kubernetes.io/docs/reference/using-api/#api-versioning

$ kubectl api-resources | more
$ kubectl api-resources --api-group=apps | more
$ kubectl api-versions | sort | more

如何操作API Object

两种模式

• Imperative Configuration (直接通过命令行去创建，操作)

• Declarative Configuration (通过YAML/JSON格式定义Manifest，把期望状态定义在文件中, 然后把文件传给API server)

apiVersion: v1
kind: Pod
metadata:
  name: web
spec:
  containers:
  - name: nginx-container
    image: nginx:latest

$ kubectl apply -f nginx.yml  # Declarative Configuration
$ kubectl run web --image=nginx # Imperative Configuration