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: 3
  selector:
    matchLabels:
      app: httpd
  template:
    metadata:
      labels:
        app: httpd
    spec:
      containers:
      - name: httpd
        image: httpd:2.2.31
        imagePullPolicy: IfNotPresent  #默认值,本地有则使用本地镜像,不拉取
        ports:
        - containerPort: 80

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:2.2.33

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      3         4         1            3           42m       httpd        httpd:2.2.33                 app=httpd
mtomcat    1         1         1            1           4d        mtomcat      liujixiao/java-demo:latest   app=mtomcat
mynginx    1         1         1            1           9d        mynginx      nginx:latest                 name=mynginx
mytomcat   1         1         1            1           9d        mytomcat     tomcat:8                     app=mytomcat
nginx      1         1         1            1           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     3         3         3         11m       httpd        httpd:2.2.32                 app=httpd,pod-template-hash=3140604099
httpd-cb5f5c5cb      1         1         0         38s       httpd        httpd:2.2.33                 app=httpd,pod-template-hash=761917176
httpd-fbdc45d78      0         0         0         42m       httpd        httpd:2.2.31                 app=httpd,pod-template-hash=968701834
mtomcat-7d6b5577b9   0         0         0         4d        mtomcat      tomcat:8                     app=mtomcat,pod-template-hash=3826113365
mtomcat-b8d9c579     1         1         1         3d        mtomcat      liujixiao/java-demo:latest   app=mtomcat,pod-template-hash=64857135
mynginx-7659f869f4   1         1         1         9d        mynginx      nginx:latest                 name=mynginx,pod-template-hash=3215942590
mytomcat-698fb6789   1         1         1         9d        mytomcat     tomcat:8                     app=mytomcat,pod-template-hash=254962345
nginx-5bc649579b     1         1         1         5d        nginx        nginx:latest                 name=nginx,pod-template-hash=1672051356
nginx-fd7dc4fbc      0         0         0         16d       nginx        nginx:latest                 name=nginx,pod-template-hash=983870967

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: 10
  replicas: 3
  selector:
    matchLabels:
      app: httpd
  template:
    metadata:
      labels:
        app: httpd
    spec:
      containers:
      - name: httpd
        image: httpd:2.4.16
        imagePullPolicy: IfNotPresent  #默认值,本地有则使用本地镜像,不拉取
        ports:
        - containerPort: 80

httpd-v2.yaml

apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: httpd
spec:
  revisionHistoryLimit: 10
  replicas: 3
  selector:
    matchLabels:
      app: httpd
  template:
    metadata:
      labels:
        app: httpd
    spec:
      containers:
      - name: httpd
        image: httpd:2.4.17
        imagePullPolicy: IfNotPresent  #默认值,本地有则使用本地镜像,不拉取
        ports:
        - containerPort: 80

httpd-v3.yaml

apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: httpd
spec:
  revisionHistoryLimit: 10
  replicas: 3
  selector:
    matchLabels:
      app: httpd
  template:
    metadata:
      labels:
        app: httpd
    spec:
      containers:
      - name: httpd
        image: httpd:2.4.18
        imagePullPolicy: IfNotPresent  #默认值,本地有则使用本地镜像,不拉取
        ports:
        - containerPort: 80

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     3         3         3            0           16s       httpd        httpd:2.4.16   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     3         4         1            0           27s       httpd        httpd:2.4.17   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     3         4         1            2           36s       httpd        httpd:2.4.18   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
1         kubectl apply --filename=httpd-v1.yaml --record=true
2         kubectl apply --filename=httpd-v2.yaml --record=true
3         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     3         3         3            3           17m       httpd        httpd:2.4.18   app=httpd

回滚版本

kubectl rollout undo deployment httpd --to-revision=1

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     3         4         3            3           19m       httpd        httpd:2.4.16   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
2         kubectl apply --filename=httpd-v2.yaml --record=true
3         kubectl apply --filename=httpd-v3.yaml --record=true
4         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。