Kubernetes资源清单篇：如何创建资源？

446 05-31

在Kubernetes中所有操作的内容，我们都称为“资源对象”，是由API Server基于HTTP/HTTPS接收并响应客户端的操作请求，是一种Restful风格的接口，将各种组件及操作内容都抽象成为标准的REST资源，如Namespace、Pod等，其中操作内容以JSON或yml格式数据进行操作。

本文讲解的是Kubernetes中的最为重要的一节——资源清单，我们想要在Kubernetes中部署Pod、Service等资源对象，都需要通过资源清单的方式来部署，无论是通过命令kubectl，还是可视化控制台，都是离不开资源清单的定义，本文重点讲述资源清单如何定义、如何创建及使用。

1、资源分类

根据资源的功能进行资源分类，Kubernetes资源对象可分为：

工作负载（Workload）：Pod、ReplicaSet、Deployment、StatefulSet、DaemonSet、Job、CronJob。
发现和负载均衡（Discovery & LB）：Service 、Ingress。
配置和存储（Config & Storage）： Volume（存储卷）、CSI（容器存储接口，可以扩展各种各样的第三方存储卷）。
集群（Cluster）：Namespace、Node、Role、ClusterRole、RoleBinding（角色绑定）、ClusterRoleBinding（集群角色绑定）。
元数据（Metadata）：HPA、PodTemplate（Pod模板，用于让控制器创建Pod时使用的模板）、LimitRange（用来定义硬件资源限制的）。

一个应用通常需要多个资源的支撑，例如，使用Deployment资源管理应用实例（Pod）、使用ConfigMap资源保存应用配置、使用Service或Ingress资源暴露服务、使用Volume资源提供外部存储等。

2.资源清单

资源清单，等同于一个剧本，能够告诉我们每一步应该怎么去做，Kubernetes接收到这么一个剧本，就能够按照这个剧本去执行，以达到我们的预期。

在Kubernetes中，一般都是通过定义资源清单的方式去创建资源。一般使用yaml格式的文件来创建符合我们预期期望的资源，这样的yaml文件我们称为资源清单。（也可以定义为json格式）

如，创建一个Pod资源：

apiVersion: v1
kind: Pod
metadata:
  name: vue-frontend
  namespace: test
  labels:
    app: vue-frontend
spec:
  containers:
  - name: vue-frontend
    image: xcbeyond/vue-frontend:latest
    ports:
      - name: port
        containerPort: 80
        hostPort: 8080

接下来，以Pod资源定义为例展开对资源清单的详细说明。

2.1 资源清单定义

yaml格式的Pod资源清单定义文件的完整内容如下：

apiVersion: v1
kind: Pod		# 资源类别
metadata:		# 资源元数据
  name: string
  namespace: string
  labels:
    - name: string
  annotations:
    - name: string
spec:			# 资源期望的状态
  containers:		# 容器列表
    - name: string		# 容器名称，下面的属性均属于对该容器的定义或约束
      image: string
        imagePullPolicy: [Always|Never|IfNotPresent]
      command: [string]
      args: [string]
      workingDir: string
      volumeMounts:
        - name: string
          mountPath: string
          readOnly: boolean
      ports:
        - name: string
          containerPort: int
          hostPort: int
          protocol: string
      env:
        - name: string
          value: string
      resources:
        limits:
          cpu: string
          memory: string
        requests:
          cpu: string
          memory: string
      livenssProbe:
        exec:
          command: [string]
        httpGet:
          path: string
          port: number
          host: string
          scheme: string
          httpHeaders:
            - name: string
              value: string
          tcpSocket:
            port: number
          initialDelaySeconds: 0
          timeoutSeconds: 0
          periodSeconds: 0
          successThreshold: 0
          failureThreshold: 0
……

对各属性的详细说明如下表所示：

（必选属性，是必须存在的，否则创建失败。）

上述列举的是常用的属性，如果想查看全部属性，可以使用命令kubectl explain pod：

[xcbeyond@bogon ~]$ kubectl explain pod
KIND:     Pod
VERSION:  v1

DESCRIPTION:
     Pod is a collection of containers that can run on a host. This resource is
     created by clients and scheduled onto hosts.

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/sig-architecture/api-conventions.md#resources

   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/sig-architecture/api-conventions.md#types-kinds

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

   spec	<Object>
     Specification of the desired behavior of the pod. More info:
     https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status

   status	<Object>
     Most recently observed status of the pod. This data may not be up to date.
     Populated by the system. Read-only. More info:
     https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status

查看属性说明，使用如下命令，如：查看pod.spec.containers

[xcbeyond@bogon ~]$ kubectl explain pod.spec.containers
KIND:     Pod
VERSION:  v1

RESOURCE: containers <[]Object>

DESCRIPTION:
     List of containers belonging to the pod. Containers cannot currently be
     added or removed. There must be at least one container in a Pod. Cannot be
     updated.

     A single application container that you want to run within a pod.

FIELDS:
   args	<[]string>
     Arguments to the entrypoint. The docker image's CMD is used if this is not
     provided. Variable references $(VAR_NAME) are expanded using the
     container's environment. If a variable cannot be resolved, the reference in
     the input string will be unchanged. The $(VAR_NAME) syntax can be escaped
     with a double $$, ie: $$(VAR_NAME). Escaped references will never be
     expanded, regardless of whether the variable exists or not. Cannot be
     updated. More info:
     https://kubernetes.io/docs/tasks/inject-data-application/define-command-argument-container/#running-a-command-in-a-shell

   command	<[]string>
     Entrypoint array. Not executed within a shell. The docker image's
     ENTRYPOINT is used if this is not provided. Variable references $(VAR_NAME)
     are expanded using the container's environment. If a variable cannot be
     resolved, the reference in the input string will be unchanged. The
     $(VAR_NAME) syntax can be escaped with a double $$, ie: $$(VAR_NAME).
     Escaped references will never be expanded, regardless of whether the
     variable exists or not. Cannot be updated. More info:
     https://kubernetes.io/docs/tasks/inject-data-application/define-command-argument-container/#running-a-command-in-a-shell
……