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使用Deployment运行一个无状态应用

本文介绍通过Kubernetes Deployment对象如何去运行一个应用.

教程目标

  • 创建一个nginx deployment.
  • 使用kubectl列举关于deployment信息.
  • 更新deployment.

准备开始

你必须拥有一个 Kubernetes 的集群，同时你的 Kubernetes 集群必须带有 kubectl 命令行工具。 如果你还没有集群，你可以通过 Minikube 构建一 个你自己的集群，或者你可以使用下面任意一个 Kubernetes 工具构建：

要获知版本信息，请输入 kubectl version.

创建和探究一个nginx deployment

你可以通过创建一个Kubernetes Deployment对象来运行一个应用, 可以在一个YAML文件中描述Deployment. 例如, 下面这个YAML文件描述了一个运行nginx:1.7.9 Docker镜像的Deployment:

application/deployment.yaml 
apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 2 # tells deployment to run 2 pods matching the template
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80

  1. 通过YAML文件创建一个Deployment:

     kubectl apply -f https://k8s.io/examples/application/deployment.yaml

  2. 展示Deployment相关信息:

    kubectl describe deployment nginx-deployment

 user@computer:~/website$ kubectl describe deployment nginx-deployment
 Name:     nginx-deployment
 Namespace:    default
 CreationTimestamp:  Tue, 30 Aug 2016 18:11:37 -0700
 Labels:     app=nginx
 Annotations:    deployment.kubernetes.io/revision=1
 Selector:   app=nginx
 Replicas:   2 desired | 2 updated | 2 total | 2 available | 0 unavailable
 StrategyType:   RollingUpdate
 MinReadySeconds:  0
 RollingUpdateStrategy:  1 max unavailable, 1 max surge
 Pod Template:
   Labels:       app=nginx
   Containers:
    nginx:
     Image:              nginx:1.7.9
     Port:               80/TCP
     Environment:        <none>
     Mounts:             <none>
   Volumes:              <none>
 Conditions:
   Type          Status  Reason
   ----          ------  ------
   Available     True    MinimumReplicasAvailable
   Progressing   True    NewReplicaSetAvailable
 OldReplicaSets:   <none>
 NewReplicaSet:    nginx-deployment-1771418926 (2/2 replicas created)
 No events.

  3. 列出deployment创建的pods:

    kubectl get pods -l app=nginx

 NAME                                READY     STATUS    RESTARTS   AGE
 nginx-deployment-1771418926-7o5ns   1/1       Running   0          16h
 nginx-deployment-1771418926-r18az   1/1       Running   0          16h

  4. 展示某一个pod信息:

    kubectl describe pod <pod-name>

    该处 <pod-name> 指某一pod的名称.

更新deployment

你可以通过更新一个新的YAML文件来更新deployment. 下面的YAML文件指定该deployment镜像更新为nginx 1.8.

application/deployment-update.yaml 
apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 2
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.16.1 # Update the version of nginx from 1.14.2 to 1.16.1
        ports:
        - containerPort: 80

  1. 应用新的YAML:

      kubectl apply -f https://k8s.io/examples/application/deployment-update.yaml

  2. 查看该deployment创建的pods以新的名称同时删除旧的pods:

      kubectl get pods -l app=nginx

通过增加副本数来弹缩应用

你可以通过应用新的YAML文件来增加Deployment中pods的数量. 该YAML文件将replicas设置为4, 指定该Deployment应有4个pods:

application/deployment-scale.yaml 
apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 4 # Update the replicas from 2 to 4
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80

  1. 应用新的YAML文件:

     kubectl apply -f https://k8s.io/examples/application/deployment-scale.yaml

  2. 验证Deployment有4个pods:

     kubectl get pods -l app=nginx

    输出的结果类似于:

     NAME                               READY     STATUS    RESTARTS   AGE
 nginx-deployment-148880595-4zdqq   1/1       Running   0          25s
 nginx-deployment-148880595-6zgi1   1/1       Running   0          25s
 nginx-deployment-148880595-fxcez   1/1       Running   0          2m
 nginx-deployment-148880595-rwovn   1/1       Running   0          2m

删除deployment

通过名称删除deployment:

kubectl delete deployment nginx-deployment

ReplicationControllers -- 旧的方式

创建一个多副本应用首选方法是使用Deployment,反过来使用ReplicaSet. 在Deployment和ReplicaSet加入到Kubernetes之前, 多副本应用通过ReplicationController来配置.

接下来