1. 简介

Deployment 背后管理着一个或多个 ReplicaSet，并通过 ReplicaSet 来管理着一组 Pod。

与 ReplicaSet 不同，Deployment 可以实现滚动更新的功能，即创建一个新的 ReplicaSet。此外，Deployment 也支持回滚，即启用旧的 ReplicaSet。

2. 用法

deploy.yaml：

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80

• 创建

  $ kubectl apply -f deploy.yaml 
  deployment.apps/nginx-deployment created
  

• 罗列

  $ kubectl get deploy
  NAME               READY   UP-TO-DATE   AVAILABLE   AGE
  nginx-deployment   3/3     3            3           118s
  

  查看背后的 ReplicaSet：

  $ kubectl get rs
  NAME                          DESIRED   CURRENT   READY   AGE
  nginx-deployment-66b6c48dd5   3         3         3       2m51s
  

  查看底层的 Pods：

  $ kubectl get pod --show-labels
  NAME                                READY   STATUS    RESTARTS   AGE     LABELS
  nginx-deployment-66b6c48dd5-9gv9c   1/1     Running   0          4m17s   app=nginx,pod-template-hash=66b6c48dd5
  nginx-deployment-66b6c48dd5-fzl5q   1/1     Running   0          4m17s   app=nginx,pod-template-hash=66b6c48dd5
  nginx-deployment-66b6c48dd5-xzm9w   1/1     Running   0          4m17s   app=nginx,pod-template-hash=66b6c48dd5
  

• 更新

  首先修改容器镜像为 nginx:1.16.1，然后执行变更：

  $ kubectl apply -f deploy.yaml 
  deployment.apps/nginx-deployment configured
  

• 查看详细信息

  $ kubectl describe deploy nginx-deployment
  Name:                   nginx-deployment
  Namespace:              default
  CreationTimestamp:      Sat, 23 Oct 2021 06:27:47 +0000
  Labels:                 <none>
  Annotations:            deployment.kubernetes.io/revision: 2
  Selector:               app=nginx
  Replicas:               3 desired | 3 updated | 3 total | 3 available | 0 unavailable
  StrategyType:           RollingUpdate
  MinReadySeconds:        0
  RollingUpdateStrategy:  25% max unavailable, 25% max surge
  Pod Template:
    Labels:  app=nginx
    Containers:
     nginx:
      Image:        nginx:1.16.1
      Port:         80/TCP
      Host Port:    0/TCP
      Environment:  <none>
      Mounts:       <none>
    Volumes:        <none>
  Conditions:
    Type           Status  Reason
    ----           ------  ------
    Available      True    MinimumReplicasAvailable
    Progressing    True    NewReplicaSetAvailable
  OldReplicaSets:  <none>
  NewReplicaSet:   nginx-deployment-559d658b74 (3/3 replicas created)
  Events:
    Type    Reason             Age    From                   Message
    ----    ------             ----   ----                   -------
    Normal  ScalingReplicaSet  8m35s  deployment-controller  Scaled up replica set nginx-deployment-66b6c48dd5 to 3
    Normal  ScalingReplicaSet  54s    deployment-controller  Scaled up replica set nginx-deployment-559d658b74 to 1
    Normal  ScalingReplicaSet  38s    deployment-controller  Scaled down replica set nginx-deployment-66b6c48dd5 to 2
    Normal  ScalingReplicaSet  38s    deployment-controller  Scaled up replica set nginx-deployment-559d658b74 to 2
    Normal  ScalingReplicaSet  34s    deployment-controller  Scaled down replica set nginx-deployment-66b6c48dd5 to 1
    Normal  ScalingReplicaSet  34s    deployment-controller  Scaled up replica set nginx-deployment-559d658b74 to 3
    Normal  ScalingReplicaSet  31s    deployment-controller  Scaled down replica set nginx-deployment-66b6c48dd5 to 0
  

  查看 Events 字段可以看出，在 Deployment 执行滚动更新时，它会不断减少旧 ReplicaSet 所管理的 Pod，直到为 0，同时不断增加新 ReplicaSet 所管理的 Pod，直至到达期望状态。

• 回滚

  首先查看 Deployment 的历史版本：

  $ kubectl rollout history deploy nginx-deployment
  deployment.apps/nginx-deployment 
  REVISION  CHANGE-CAUSE
  1         <none>
  2         <none>
  

  查看某个版本的具体信息：

  $ kubectl rollout history deploy nginx-deployment --revision=1
  deployment.apps/nginx-deployment with revision #1
  Pod Template:
    Labels:       app=nginx
          pod-template-hash=66b6c48dd5
    Containers:
     nginx:
      Image:      nginx:1.14.2
      Port:       80/TCP
      Host Port:  0/TCP
      Environment:        <none>
      Mounts:     <none>
    Volumes:      <none>
  

  回滚到具体的版本：

  $ kubectl rollout undo deploy nginx-deployment --to-revision=1
  deployment.apps/nginx-deployment rolled back
  

  回滚到上个版本：

  $ kubectl rollout undo deploy nginx-deployment
  

• 暂停

  $ kubectl rollout pause deploy nginx-deployment
  deployment.apps/nginx-deployment paused
  

• 恢复

  $ kubectl rollout resume deploy nginx-deployment
  deployment.apps/nginx-deployment resumed
  

• 删除

  $ kubectl delete -f deploy.yaml 
  deployment.apps "nginx-deployment" deleted
  

  连带着删除其背后的 ReplicaSet 和 Pod。