Kubernetes資源清單篇：如何創(chuàng)建資源？
在Kubernetes中所有操作的內(nèi)容，我們都稱為“資源對(duì)象”，是由API Server基于HTTP/HTTPS接收并響應(yīng)客戶端的操作請(qǐng)求，是一種Restful風(fēng)格的接口，將各種組件及操作內(nèi)容都抽象成為標(biāo)準(zhǔn)的REST資源，如Namespace、Pod等，其中操作內(nèi)容以JSON或yml格式數(shù)據(jù)進(jìn)行操作。本文講解的是Kubernetes中的最為重要的一節(jié)——資源清單，我們想要在Kubernetes中部署Pod、Service等資源對(duì)象，都需要通過資源清單的方式來部署，無論是通過命令kubectl，還是可視化控制臺(tái)，都是離不開資源清單的定義，本文重點(diǎn)講述資源清單如何定義、如何創(chuàng)建及使用。
1、資源分類
根據(jù)資源的功能進(jìn)行資源分類，Kubernetes資源對(duì)象可分為：
- 工作負(fù)載(Workload)：Pod、ReplicaSet、Deployment、StatefulSet、DaemonSet、Job、CronJob。
- 發(fā)現(xiàn)和負(fù)載均衡(Discovery & LB)：Service 、Ingress。
- 配置和存儲(chǔ)(Config & Storage)：Volume(存儲(chǔ)卷)、CSI(容器存儲(chǔ)接口，可以擴(kuò)展各種各樣的第三方存儲(chǔ)卷)。
- 集群(Cluster)：Namespace、Node、Role、ClusterRole、RoleBinding(角色綁定)、ClusterRoleBinding(集群角色綁定)。
- 元數(shù)據(jù)(Metadata)：HPA、PodTemplate(Pod模板，用于讓控制器創(chuàng)建Pod時(shí)使用的模板)、LimitRange(用來定義硬件資源限制的)。
一個(gè)應(yīng)用通常需要多個(gè)資源的支撐，例如，使用Deployment資源管理應(yīng)用實(shí)例(Pod)、使用ConfigMap資源保存應(yīng)用配置、使用Service或Ingress資源暴露服務(wù)、使用Volume資源提供外部存儲(chǔ)等。
2.資源清單
資源清單，等同于一個(gè)劇本，能夠告訴我們每一步應(yīng)該怎么去做，Kubernetes接收到這么一個(gè)劇本，就能夠按照這個(gè)劇本去執(zhí)行，以達(dá)到我們的預(yù)期。在Kubernetes中，一般都是通過定義資源清單的方式去創(chuàng)建資源。一般使用yaml格式的文件來創(chuàng)建符合我們預(yù)期期望的資源，這樣的yaml文件我們稱為資源清單。(也可以定義為json格式)如，創(chuàng)建一個(gè)Pod資源：
- 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
接下來，以Pod資源定義為例展開對(duì)資源清單的詳細(xì)說明。
2.1 資源清單定義
yaml格式的Pod資源清單定義文件的完整內(nèi)容如下：
- apiVersion: v1
- kind: Pod # 資源類別
- metadata: # 資源元數(shù)據(jù)
- name: string
- namespace: string
- labels:
- - name: string
- annotations:
- - name: string
- spec: # 資源期望的狀態(tài)
- containers: # 容器列表
- - name: string # 容器名稱，下面的屬性均屬于對(duì)該容器的定義或約束
- 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
- ……
對(duì)各屬性的詳細(xì)說明如下表所示：(必選屬性，是必須存在的，否則創(chuàng)建失敗。)
上述列舉的是常用的屬性，如果想查看全部屬性，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
查看屬性說明，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
在命名空間test中，定義一個(gè)名為frontend的Pod。
(1)定義命名空間
為了便于后期測(cè)試，特定義一個(gè)新的命名空間test。(如果命名空間test已存在，則無需再建)
命名空間test的資源清單文件test-namespace.yaml如下：
- apiVersion: v1
- kind: Namespace
- metadata:
- name: test
執(zhí)行kubectl create命令創(chuàng)建該Namespace：
- [xcbeyond@bogon ~]$ kubectl create -f test-namespace.yaml
- namespace/test created
(2)定義Pod
定義一個(gè)名為frontend的Pod，由一個(gè)容器組成，資源清單文件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
執(zhí)行kubectl create命令創(chuàng)建該P(yáng)od：
- [xcbeyond@bogon ~]$ kubectl create -f frontend-pod.yaml
- pod/frontend created
通過命令kubectl get pods -n
- [xcbeyond@bogon ~]$ kubectl get pods -n test
- NAME READY STATUS RESTARTS AGE
- frontend 1/1 Runing 0 79s
