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kubernetes Deployment之滚动更新策略。

1.Deployment控制器详细信息中包含了其更新策略的相关配置。kubectl describe命令中输出的StrategyType、RollingUpdateStrategy字段等；

root@kubernetes-master01:~# kubectl describe deploy sleep
Name:                   sleep
Namespace:              default
CreationTimestamp:      Wed, 25 May 2022 15:03:14 +0800
Labels:                 <none>
Annotations:            deployment.kubernetes.io/revision: 1
Selector:               app=sleep
Replicas:               1 desired | 1 updated | 1 total | 1 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        0
RollingUpdateStrategy:  25% max unavailable, 25% max surge
# Deployment默认更新策略就是RollingUpdate默认更新策略是25%

1.Deployment的更新策略:

Deployment控制器支持两种更新策略: 滚动更新(rolling update)和重建创建(recreate)也称为单批次更新。
1.重建(Recreate)，当更新策略设定为Recreate，在更新镜像时，它会先删除现在正在运行的Pod，等彻底杀死后，重新创建新的RS(ReplicaSet)然后启动对应的Pod，在整个更新过程中，会造成服务一段时间无法提供服务。也称之为单批次更新。
2.滚动更新(Rolling Update)滚动更新是默认的更新策略，一次仅更新一批Pod，当更新的Pod就绪后再更新另一批，直到全部更新完成为止；该策略实现了不间断服务的目标，但是在更新过程中，不同客户端得到的响应内容可能会来自不同版本的应用。会出现新老版本共存状态。

2.ReCreate实践；

Recreate分为三个步骤:
1.杀死所有旧版本的Pod，此时Pod无法正常对外提供服务；
2.创建新的RS，启动新的Pod；
3.等待Pod就绪，对外提供服务；

2.1应用配置示例

# 须在Spec字段中明确定义strategy滚动更新策略和type类型
root@kubernetes-master01:~# cat nginx-deployment-test.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: deployment-nginx-test
  namespace: default
spec:
  strategy:         # 滚动更新策略
    type: Recreate  # Recreate表示的是单批次更新。
  replicas: 2
  selector:
    matchLabels:
      app: nginx-deployment

  template:
    metadata:
      labels:
        app: nginx-deployment
    spec:
      containers:
      - name: nginx
        image: nginx:1.16
        #imagePullPolicy: IfNotPresent
        ports:
        - name: http
          containerPort: 80
root@kubernetes-master01:~# kubectl apply -f nginx-deployment-test.yaml

2.2访问测试，同时配置文件修改Nginx的版本测试服务是否会中断；

# 跟上任何符号会报错Nginx的错误页，现版本是1.16。当然是为了证实nginx版本。
root@kubernetes-master01:~# curl 10.107.246.117/v
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.16.1</center>
</body>
</html>

2.3现版本是1.16，现在测试滚动更新；

1.修改yaml配置文件修改编辑配置文件的spec.containers.image字段修改Nginx的版本
2.通过set image来修改

我是通过set image来修改。
root@kubernetes-master01:~# kubectl set image deployment/deployment-nginx-test nginx=nginx:latest
deployment.apps/deployment-nginx-test image updated

2.4访问测试，的确中间是有业务访问间断的，因此在生产环境不建议这种方式。在更新的过程中旧Pod是处于Terminating状态。

root@kubernetes-master01:~# while sleep 0.5; do curl http://10.107.246.117/version;done
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.16.1</center>
</body>
</html>
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.16.1</center>
</body>
</html>
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.16.1</center>
</body>
</html>
<html>
curl: (7) Failed to connect to 10.107.246.117 port 80: Connection refused
curl: (7) Failed to connect to 10.107.246.117 port 80: Connection refused
curl: (7) Failed to connect to 10.107.246.117 port 80: Connection refused
curl: (7) Failed to connect to 10.107.246.117 port 80: Connection refused
curl: (7) Failed to connect to 10.107.246.117 port 80: Connection refused
curl: (7) Failed to connect to 10.107.246.117 port 80: Connection refused
curl: (7) Failed to connect to 10.107.246.117 port 80: Connection refused
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.21.5</center>
</body>
</html>
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.21.5</center>
</body>
</html>
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.21.5</center>
</body>
</html>

3.RollingUpdate实践

滚动更新时，应用升级期间还要确保可用的Pod对象数量不低于阈值以确保可用持续处理客户端的服务请求，变动的方式和Pod对象的数量范围将通过spec.strategy.rollingUpdate.maxSurge和spec.strategy.rollingPudate.maxUnavailable两个属性同时进行定义；

滚动更新(RollingUpdate)一次仅更新一批Pod，当更新的Pod就绪后，再更新另一批，直到全部更新完成为止，该策略实现了不间断服务的目标，在更新过程中可能会出现不同的应用版本且并存，同时提供服务的情况。

1.创建新的RS，然后根据新的镜像运行新的Pod。
2.删除旧的Pod，启动新的Pod，当新Pod就绪后，继续删除旧Pod，启动新Pod。
3.持续第二步过程，一直到所有Pod都被更新成功。

3.1准备应用配置文件

# 这个字段需配置为RollingUpdate
spec:
  strategy:
    type: RollingUpdate
# 应用配置文件,现版本Nginx是1.16版本，要滚动到1.21.5
root@kubernetes-master01:~# cat nginx-deployment-test.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: deployment-nginx-test
  namespace: default
spec:
  strategy:
    type: RollingUpdate
  replicas: 2
  selector:
    matchLabels:
      app: nginx-deployment

  template:
    metadata:
      labels:
        app: nginx-deployment
    spec:
      containers:
      - name: nginx
        image: nginx:1.16
        #imagePullPolicy: IfNotPresent
        ports:
        - name: http
          containerPort: 80
root@kubernetes-master01:~# kubectl apply -f nginx-deployment-test.yaml
deployment.apps/deployment-nginx-test created

# Pod也是运行正常的。
root@kubernetes-master01:~# kubectl get pods -l app=nginx-deployment
NAME                                     READY   STATUS    RESTARTS   AGE
deployment-nginx-test-65b579f8d5-gdpd5   1/1     Running   0          3m14s
deployment-nginx-test-65b579f8d5-spq9w   1/1     Running   0          3m14s

3.2，我们现在访问前端的Service；OK版本一直是1.16；

root@kubernetes-master01:~# while sleep 0.5; do curl http://10.103.162.78/v;done
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.16.1</center>
</body>
</html>
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.16.1</center>
</body>
</html>
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.16.1</center>

3.3修改yaml配置文件升级；并观察是否业务中断；

# Pod状态；1.16版本的Pod是65b579f8d5，现在是76f7b87b7c
root@kubernetes-master01:~# kubectl get pods
deployment-nginx-test-76f7b87b7c-n2jmm       1/1     Running             0          35s
deployment-nginx-test-76f7b87b7c-qvxhg       0/1     ContainerCreating   0          11s

# 滚动升级状态；
root@kubernetes-master01:~# kubectl apply -f nginx-deployment-test.yaml  && kubectl rollout status deploy deployment-nginx-test
deployment.apps/deployment-nginx-test configured
Waiting for deployment "deployment-nginx-test" rollout to finish: 1 out of 2 new replicas have been updated...
Waiting for deployment "deployment-nginx-test" rollout to finish: 1 out of 2 new replicas have been updated...
Waiting for deployment "deployment-nginx-test" rollout to finish: 1 out of 2 new replicas have been updated...
Waiting for deployment "deployment-nginx-test" rollout to finish: 1 old replicas are pending termination...
Waiting for deployment "deployment-nginx-test" rollout to finish: 1 old replicas are pending termination...
deployment "deployment-nginx-test" successfully rolled out

# 查看Replicaset；现在65b579的Pod数量被置于0
root@kubernetes-master01:~# kubectl get replicaset
deployment-nginx-test-577977f4b6       2         2         2       7m
deployment-nginx-test-65b579f8d5       0         0         0       17m

3.4观察访问

# 业务访问正常，没有中断，但是一段时间会出现新老版本共存状态；
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.21.5</center>
</body>
</html>
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.16.1</center>
</body>
</html>
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.21.5</center>
</body>
</html>
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.16.1</center>
</body>
</html>
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.21.5</center>
</body>
</html>
^C

4.应用的回滚

4.1.我们可以通过命令来查看更新的历史版本；

root@kubernetes-master01:~# kubectl  rollout history  deployment deployment-nginx-test
deployment.apps/deployment-nginx-test
REVISION  CHANGE-CAUSE
1         <none>
2         <none>

4.2.也可以查看具体镜像详情,跟上序号；

root@kubernetes-master01:~# kubectl rollout history deploy  deployment-nginx-test --revision=2
deployment.apps/deployment-nginx-test with revision #2
Pod Template:
  Labels:	app=nginx-deployment
	pod-template-hash=76f7b87b7c
  Containers:
   nginx:
    Image:	nginx:1.16
    Port:	80/TCP
    Host Port:	0/TCP
    Environment:	<none>
    Mounts:	<none>
  Volumes:	<none>

4.3.现在想要回滚到1.16这个版本；

root@kubernetes-master01:~# kubectl rollout undo deploy  deployment-nginx-test  --to-revision=2 && kubectl rollout status deploy deployment-nginx-test
deployment.apps/deployment-nginx-test rolled back
Waiting for deployment "deployment-nginx-test" rollout to finish: 1 out of 2 new replicas have been updated...
Waiting for deployment "deployment-nginx-test" rollout to finish: 1 out of 2 new replicas have been updated...
Waiting for deployment "deployment-nginx-test" rollout to finish: 1 out of 2 new replicas have been updated...
Waiting for deployment "deployment-nginx-test" rollout to finish: 1 old replicas are pending termination...
Waiting for deployment "deployment-nginx-test" rollout to finish: 1 old replicas are pending termination...
deployment "deployment-nginx-test" successfully rolled out

4.4.观察访问状态；亦会出现新老版本交替情况

<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.21.5</center>
</body>
</html>
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.16.1</center>
</body>
</html>
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.21.5</center>
</body>
</html>
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.16.1</center>
</body>
</html>
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.21.5</center>
</body>
</html>
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.16.1</center>
</body>
</html>
^C

4.5.查看Pod和Replicaset

root@kubernetes-master01:~/cloud-Native/deployment/replicas# kubectl get pods -l app=nginx-deployment
NAME                                     READY   STATUS    RESTARTS   AGE
deployment-nginx-test-76f7b87b7c-5tx7z   1/1     Running   0          2m34s
deployment-nginx-test-76f7b87b7c-t9ld2   1/1     Running   0          2m57s

# 也是没有问题。
root@kubernetes-master01:~/cloud-Native/deployment/replicas# kubectl get replicaset -l app=nginx-deployment
NAME                               DESIRED   CURRENT   READY   AGE
deployment-nginx-test-577977f4b6   0         0         0       20m
deployment-nginx-test-65b579f8d5   0         0         0       31m
deployment-nginx-test-76f7b87b7c   2         2         2       24m
07-28 12:53
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