linux运维、架构之路-K8s滚动更新及回滚

一、滚动更新

       应用程序一次只更新一小部分副本，更新成功后，再更新更多的副本，最终完成所有副本的更新。 滚动更新的优点：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。

1、创建三个副本Httpd服务，初始镜像为httpd:2.2.31，然后滚动更新至httpd:2.2.32

###cat httpd.yaml###
apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: httpd
spec:
  replicas:
  selector:
    matchLabels:
      app: httpd
  template:
    metadata:
      labels:
        app: httpd
    spec:
      containers:
      - name: httpd
        image: httpd:2.2.
        imagePullPolicy: IfNotPresent  #默认值,本地有则使用本地镜像,不拉取
        ports:
        - containerPort: 

①创建

kubectl apply -f httpd.yaml

②查看

③修改deployment文件进行更新

 应用

kubectl apply -f httpd.yaml --record

④再次查看更新后的httpd版本

⑤使用命令查看滚动更新详细

kubectl describe deployment httpd

 结果：每次只更新替换一个pod副本

⑥使用命令替换镜像

kubectl set image deployments/httpd httpd=httpd:2.2.

⑦验证如下：

[root@k8s-node1 rolling]# kubectl get deployment -o wide
NAME       DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE       CONTAINERS   IMAGES                       SELECTOR
httpd                                               42m       httpd        httpd:2.2.                 app=httpd
mtomcat                                             4d        mtomcat      liujixiao/java-demo:latest   app=mtomcat
mynginx                                             9d        mynginx      nginx:latest                 name=mynginx
mytomcat                                            9d        mytomcat     tomcat:                     app=mytomcat
nginx                                               16d       nginx        nginx:latest                 name=nginx
[root@k8s-node1 rolling]# kubectl get rs -o wide
NAME                 DESIRED   CURRENT   READY     AGE       CONTAINERS   IMAGES                       SELECTOR
httpd-7584b484ff                                11m       httpd        httpd:2.2.                 app=httpd,pod-template-hash=
httpd-cb5f5c5cb                                 38s       httpd        httpd:2.2.                 app=httpd,pod-template-hash=
httpd-fbdc45d78                                 42m       httpd        httpd:2.2.                 app=httpd,pod-template-hash=
mtomcat-7d6b5577b9                              4d        mtomcat      tomcat:                     app=mtomcat,pod-template-hash=
mtomcat-b8d9c579                                3d        mtomcat      liujixiao/java-demo:latest   app=mtomcat,pod-template-hash=
mynginx-7659f869f4                              9d        mynginx      nginx:latest                 name=mynginx,pod-template-hash=
mytomcat-698fb6789                              9d        mytomcat     tomcat:                     app=mytomcat,pod-template-hash=
nginx-5bc649579b                                5d        nginx        nginx:latest                 name=nginx,pod-template-hash=
nginx-fd7dc4fbc                                 16d       nginx        nginx:latest                 name=nginx,pod-template-hash=

二、回滚

kubectl apply每次更新应用时，都会记录下当前的配置文件，保存为一个revision (版本)，这样就可以通过这个版本回滚到特定的时间。默认配置下，K8s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reviseion数量。

1、实践回滚功能

①创建三个应用配置文件httpd-v1.yaml、httpd-v2.yaml、httpd-v3.yaml

httpd-v1.yaml

apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: httpd
spec:
  revisionHistoryLimit:
  replicas:
  selector:
    matchLabels:
      app: httpd
  template:
    metadata:
      labels:
        app: httpd
    spec:
      containers:
      - name: httpd
        image: httpd:2.4.
        imagePullPolicy: IfNotPresent  #默认值,本地有则使用本地镜像,不拉取
        ports:
        - containerPort: 

httpd-v2.yaml

apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: httpd
spec:
  revisionHistoryLimit:
  replicas:
  selector:
    matchLabels:
      app: httpd
  template:
    metadata:
      labels:
        app: httpd
    spec:
      containers:
      - name: httpd
        image: httpd:2.4.
        imagePullPolicy: IfNotPresent  #默认值,本地有则使用本地镜像,不拉取
        ports:
        - containerPort: 

httpd-v3.yaml

apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: httpd
spec:
  revisionHistoryLimit:
  replicas:
  selector:
    matchLabels:
      app: httpd
  template:
    metadata:
      labels:
        app: httpd
    spec:
      containers:
      - name: httpd
        image: httpd:2.4.
        imagePullPolicy: IfNotPresent  #默认值,本地有则使用本地镜像,不拉取
        ports:
        - containerPort: 

②通过kubectl apply部署并更新应用

kubectl apply -f httpd-v1.yaml --record
deployment.apps "httpd" created
[root@k8s-node1 rolling]# kubectl get deployment httpd -o wide
NAME      DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE       CONTAINERS   IMAGES         SELECTOR
httpd                                              16s       httpd        httpd:2.4.   app=httpd
[root@k8s-node1 rolling]# kubectl apply -f httpd-v2.yaml --record
deployment.apps "httpd" configured
[root@k8s-node1 rolling]#
[root@k8s-node1 rolling]#
[root@k8s-node1 rolling]# kubectl get deployment httpd -o wide
NAME      DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE       CONTAINERS   IMAGES         SELECTOR
httpd                                              27s       httpd        httpd:2.4.   app=httpd
[root@k8s-node1 rolling]# kubectl apply -f httpd-v3.yaml --record
deployment.apps "httpd" configured
[root@k8s-node1 rolling]#
[root@k8s-node1 rolling]#
[root@k8s-node1 rolling]#
[root@k8s-node1 rolling]# kubectl get deployment httpd -o wide
NAME      DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE       CONTAINERS   IMAGES         SELECTOR
httpd                                              36s       httpd        httpd:2.4.   app=httpd

--record的作用是将当前命令记录到revision 记录中，这样我们就可以知道每个revison对应的是哪个配置文件，
通过kubectl rollout history deployment httpd查看历史记录，如下图：

[root@k8s-node1 rolling]# kubectl rollout history deployment httpd
deployments "httpd"
REVISION  CHANGE-CAUSE
         kubectl apply --filename=httpd-v1.yaml --record=true
         kubectl apply --filename=httpd-v2.yaml --record=true
         kubectl apply --filename=httpd-v3.yaml --record=true

③回滚到某个版本

查看当前版本：

[root@k8s-node1 rolling]# kubectl get deployment httpd -o wide
NAME      DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE       CONTAINERS   IMAGES         SELECTOR
httpd                                              17m       httpd        httpd:2.4.   app=httpd

回滚版本

kubectl rollout undo deployment httpd --to-revision=

查看回滚后版本

[root@k8s-node1 rolling]# kubectl get deployment httpd -o wide
NAME      DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE       CONTAINERS   IMAGES         SELECTOR
httpd                                              19m       httpd        httpd:2.4.   app=httpd

此时再查看历史记录也会发生相应的变化：

[root@k8s-node1 rolling]# kubectl rollout history deployment httpd
deployments "httpd"
REVISION  CHANGE-CAUSE
         kubectl apply --filename=httpd-v2.yaml --record=true
         kubectl apply --filename=httpd-v3.yaml --record=true
         kubectl apply --filename=httpd-v1.yaml --record=true

CHANGE-CAUSE就是--record的结果，这里可以通过CHANGE-CAUSE知道每个revision的具体含义，所以执行kubect apply时加上--record参数。