Kubernetes资源清单篇：如何创建资源？
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
- 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
- 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
- Standard object's metadata. More info:
- https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata
- spec
- 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
- 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
- ……
2.2 示例
在命名空间test中，定义一个名为frontend的Pod。
(1)定义命名空间
为了便于后期测试，特定义一个新的命名空间test。(如果命名空间test已存在，则无需再建)
命名空间test的资源清单文件test-namespace.yaml如下：
- apiVersion: v1
- kind: Namespace
- metadata:
- name: test
执行kubectl create命令创建该Namespace：
- [xcbeyond@bogon ~]$ kubectl create -f test-namespace.yaml
- namespace/test created
(2)定义Pod
定义一个名为frontend的Pod，由一个容器组成，资源清单文件frontend-pod.yaml如下：
- apiVersion: v1
- kind: Pod
- metadata:
- name: frontend
- namespace: test
- labels:
- app: frontend
- spec:
- containers:
- - name: frontend
- image: xcbeyond/vue-frontend:latest
- ports:
- - name: port
- containerPort: 80
- hostPort: 8080
执行kubectl create命令创建该Pod：
- [xcbeyond@bogon ~]$ kubectl create -f frontend-pod.yaml
- pod/frontend created
通过命令kubectl get pods -n 查看，创建Pod的状态：
- [xcbeyond@bogon ~]$ kubectl get pods -n test
- NAME READY STATUS RESTARTS AGE
- frontend 1/1 Runing 0 79s
标题名称：Kubernetes资源清单篇：如何创建资源？
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