Kubernetes Pod应用的滚动更新(八)

一、环境准备

我们紧接上一节的环境,进行下面的操作,如果不清楚的,可以先查看上一篇博文。

滚动更新是一次只更新一小部分副本,成功后,再更新更多的副本,最终完成所有副本的更新。滚动更新的最大的好处是零停机,整个更新过程始终有副本在运行,从而保证了业务的连续性。

二、更新

我们查看一下上一节的配置文件mytest-deploy.yaml

apiVersion: extensions/v1beta1kind: Deploymentmetadata: name: mytestspec: replicas: 3 template: metadata: labels: run: mytest spec: containers: - name: mytest image: wangzan18/mytest:v1 ports: - containerPort: 80

我们看到设定的镜像版本为v1,我们查看一下创建的ReplicaSet

[root@master ~]# kubectl get rs -o wideNAME DESIRED CURRENT READY AGE CONTAINERS IMAGES SELECTORmytest-88d46bf99 3 3 3 68m mytest wangzan18/mytest:v1 pod-template-hash=88d46bf99,run=mytest

目前运行的 Pod 由 ReplicaSet mytest-88d46bf99进行控制,我们将配置文件中的 v1 替换为 v2,再次应用。

[root@master ~]# kubectl apply -f mytest-deploy.yaml deployment.extensions/mytest configured[root@master ~]# kubectl get podsNAME READY STATUS RESTARTS AGEmytest-56c55b4c6-6gjxc 1/1 Running 0 24smytest-56c55b4c6-f5trx 1/1 Running 0 18smytest-56c55b4c6-sh5wd 1/1 Running 0 24smytest-88d46bf99-48f6n 1/1 Terminating 0 70mmytest-88d46bf99-mv6cf 1/1 Terminating 0 70mmytest-88d46bf99-p9w79 1/1 Terminating 0 70m
[root@master ~]# kubectl get deploy -o wideNAME READY UP-TO-DATE AVAILABLE AGE CONTAINERS IMAGES SELECTORmytest 3/3 3 3 72m mytest wangzan18/mytest:v2 run=mytest[root@master ~]# kubectl get rs -o wideNAME DESIRED CURRENT READY AGE CONTAINERS IMAGES SELECTORmytest-56c55b4c6 3 3 3 59s mytest wangzan18/mytest:v2 pod-template-hash=56c55b4c6,run=mytestmytest-88d46bf99 0 0 0 71m mytest wangzan18/mytest:v1 pod-template-hash=88d46bf99,run=mytest

我们可以看到 Deployment 的镜像更新为wangzan18/mytest:v2,创建了新的 ReplicaSet mytest-56c55b4c6,并管理了三个新的 Pod。

[root@master ~]# kubectl describe deployment mytestEvents: Type Reason Age From Message ---- ------ ---- ---- ------- Normal ScalingReplicaSet 4m9s deployment-controller Scaled up replica set mytest-56c55b4c6 to 1 Normal ScalingReplicaSet 4m9s deployment-controller Scaled down replica set mytest-88d46bf99 to 2 Normal ScalingReplicaSet 4m9s deployment-controller Scaled up replica set mytest-56c55b4c6 to 2 Normal ScalingReplicaSet 4m3s deployment-controller Scaled down replica set mytest-88d46bf99 to 1 Normal ScalingReplicaSet 4m3s deployment-controller Scaled up replica set mytest-56c55b4c6 to 3 Normal ScalingReplicaSet 4m3s deployment-controller Scaled down replica set mytest-88d46bf99 to 0

每次只更新替换一个 Pod。

三、回滚

kubectl apply 每次更新应用时 Kubernetes 都会记录下当前的配置,保存为一个 revision(版次),这样就可以回滚到某个特定 revision。

默认配置下,Kubernetes 只会保留最近的几个 revision,可以在 Deployment 配置文件中通过 revisionHistoryLimit 属性增加 revision 数量。

通过命令kubectl rollout undo我们可以回滚到上一个版本。

[root@master ~]# kubectl rollout undo deploy mytestdeployment.extensions/mytest rolled back
[root@master ~]# kubectl get rs -o wideNAME DESIRED CURRENT READY AGE CONTAINERS IMAGES SELECTORmytest-56c55b4c6 0 0 0 12m mytest wangzan18/mytest:v2 pod-template-hash=56c55b4c6,run=mytestmytest-88d46bf99 3 3 3 82m mytest wangzan18/mytest:v1 pod-template-hash=88d46bf99,run=mytest

可以看到三个 Pod 重新由镜像为wangzan18/mytest:v1的ReplicaSet进行接管。

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