Kubernetes

Kubernetes 使用RollingUpdate佈署策略, 以nginx為例

Posted by Kubeguts on 2020-10-19

Step 1 運行基本環境

準備用來部署的yaml檔案如下，為設置 4個持續運行nginx的容器

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apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-nginx
  labels:
    app: my-nginx
spec:
  replicas: 4
  minReadySeconds: 1 # Default 0
  progressDeadlineSeconds: 60 # Default 600s
  revisionHistoryLimit: 5  #Default 10
  strategy:
    type: RollingUpdate # This is the default
    rollingUpdate:
      maxSurge: 1  #Default 25%
      maxUnavailable: 1  # Default 25%
  selector:
    matchLabels:
      app: my-nginx
  template:
    metadata:
      labels:
        app: my-nginx
    spec:
      containers:
      - name: my-nginx
        image: nginx:1.16.1-alpine  #nginx:1.17.8-alpine
        ports:
        - containerPort: 80
        resources:
          limits:
            memory: "128Mi" #128 MB
            cpu: "200m" #200 millicpu (.2 cpu or 20% of the cpu)

定義nginx的service

nginx.service.yml

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kind: Service
apiVersion: v1
metadata:
  name: nginx-service
  labels:
    app: my-nginx
spec:
  type: LoadBalancer
  selector:
    app: my-nginx
  ports:
    - port: 80
      targetPort: 80

接著執行運行指令

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// 透過deployment創建具備4個container的nginx服務
$ kubectl create -f nginx.deployment.yml --save-config --record

// 定義負載平衡與流量管理
$ kubectl create -f nginx.service.yml --save-config --record
service/nginx-service created

--record 可以紀錄rollout的過程紀錄，方便後續執行rolling back動作

可以看到4個nginx的容器正在同一個pod運行中

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$ kubectl get all
NAME                            READY   STATUS    RESTARTS   AGE
pod/my-nginx-75bbd45cb9-2k7gg   1/1     Running   0          15m
pod/my-nginx-75bbd45cb9-4j5zn   1/1     Running   0          15m
pod/my-nginx-75bbd45cb9-5glbj   1/1     Running   0          15m
pod/my-nginx-75bbd45cb9-nhxpx   1/1     Running   0          15m

NAME                    TYPE           CLUSTER-IP     EXTERNAL-IP   PORT(S)        AGE
service/kubernetes      ClusterIP      10.96.0.1      <none>        443/TCP        4d11h
service/nginx-service   LoadBalancer   10.104.214.7   localhost     80:31533/TCP   4m25s

NAME                       READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/my-nginx   4/4     4            4           15m

NAME                                  DESIRED   CURRENT   READY   AGE
replicaset.apps/my-nginx-75bbd45cb9   4         4         4       15m

這時準備一個測試是否是可執行 zero downtime的腳本

確認nginx服務是否能夠回傳首頁

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for ((i=1;i<=100;i++)); 
do
    curl -s "http://localhost" | grep "<title>.*</title>"
    sleep 2s
done

這時可看到nginx服務正在運作中

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$ bash curl-loop.sh 
<title>Welcome to nginx!</title>
<title>Welcome to nginx!</title>
<title>Welcome to nginx!</title>
<title>Welcome to nginx!</title>

Step 2. 更換版本並移轉

若要更換 nginx版本 從 nginx:1.16.1-alpine 到 nginx:1.17.8-alpine

更改nginx.deployment.yml檔案，並使用 kubectl apply -f nginx.deployment.yml

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```yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-nginx
  labels:
    app: my-nginx
spec:
  replicas: 4
  minReadySeconds: 1 # Default 0
  progressDeadlineSeconds: 60 # Default 600s
  revisionHistoryLimit: 5  #Default 10
  strategy:
    type: RollingUpdate # This is the default
    rollingUpdate:
      maxSurge: 1  #Default 25%
      maxUnavailable: 1  # Default 25%
  selector:
    matchLabels:
      app: my-nginx
  template:
    metadata:
      labels:
        app: my-nginx
    spec:
      containers:
      - name: my-nginx
        image: nginx:1.17.8-alpine     (更換成新版的nginx)

...

接著快速的執行 kubectl get all 查看目前Rolling Update狀況

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$ kubectl get all
NAME                            READY   STATUS              RESTARTS   AGE
pod/my-nginx-6b8f7cd7cc-2vk7g   0/1     ContainerCreating   0          6s
pod/my-nginx-6b8f7cd7cc-596cv   0/1     ContainerCreating   0          5s
pod/my-nginx-75bbd45cb9-2k7gg   1/1     Running             0          36h
pod/my-nginx-75bbd45cb9-4j5zn   0/1     Terminating         0          36h
pod/my-nginx-75bbd45cb9-5glbj   1/1     Running             0          36h
pod/my-nginx-75bbd45cb9-nhxpx   1/1     Running             0          36h

NAME                    TYPE           CLUSTER-IP     EXTERNAL-IP   PORT(S)        AGE
service/kubernetes      ClusterIP      10.96.0.1      <none>        443/TCP        5d22h
service/nginx-service   LoadBalancer   10.104.214.7   localhost     80:31533/TCP   35h

NAME                       READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/my-nginx   3/4     2            3           36h

NAME                                  DESIRED   CURRENT   READY   AGE
replicaset.apps/my-nginx-6b8f7cd7cc   2         2         0       6s
replicaset.apps/my-nginx-75bbd45cb9   3         3         3       36h

再過一會兒，可看到目前的Pod一樣維持4個nginx服務

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$ kubectl get all
NAME                            READY   STATUS    RESTARTS   AGE
pod/my-nginx-6b8f7cd7cc-2vk7g   1/1     Running   0          56s
pod/my-nginx-6b8f7cd7cc-596cv   1/1     Running   0          55s
pod/my-nginx-6b8f7cd7cc-5wn5d   1/1     Running   0          41s
pod/my-nginx-6b8f7cd7cc-j9zzk   1/1     Running   0          36s

NAME                    TYPE           CLUSTER-IP     EXTERNAL-IP   PORT(S)        AGE
service/kubernetes      ClusterIP      10.96.0.1      <none>        443/TCP        5d22h
service/nginx-service   LoadBalancer   10.104.214.7   localhost     80:31533/TCP   35h

NAME                       READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/my-nginx   4/4     4            4           36h

NAME                                  DESIRED   CURRENT   READY   AGE
replicaset.apps/my-nginx-6b8f7cd7cc   4         4         4       56s
replicaset.apps/my-nginx-75bbd45cb9   0         0         0       36h

可看到版本移轉完畢後有兩個replicaSets

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NAME                                  DESIRED   CURRENT   READY   AGE
replicaset.apps/my-nginx-6b8f7cd7cc   4         4         4       56s
replicaset.apps/my-nginx-75bbd45cb9   0         0         0       36h

Step 3：查看移轉狀態

使用 kubectl rollout status deployment <name> 查看rollout狀態

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$ kubectl rollout status deployment my-nginx
deployment "my-nginx" successfully rolled out

再次查看 curl-loop.sh 腳本的運作，可看到移轉過程中，都沒有中斷！

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$ bash curl-loop.sh

<title>Welcome to nginx!</title>
<title>Welcome to nginx!</title>
<title>Welcome to nginx!</title>
<title>Welcome to nginx!</title>
...
<title>Welcome to nginx!</title>
<title>Welcome to nginx!</title>
<title>Welcome to nginx!</title>

Step 4：執行回滾 (rollback)

使用 kubectl rollout history deployment [name] 查看移轉歷史紀錄

查看一下移轉後的歷史紀錄revision=2的內容：

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kubectl rollout history deployment my-nginx --revision=2

deployment.apps/my-nginx with revision #2
Pod Template:
  Labels:	app=my-nginx
	pod-template-hash=6b8f7cd7cc
  Annotations:	kubernetes.io/change-cause: kubectl create --filename=nginx.deployment.yml --save-config=true --record=true
  Containers:
   my-nginx:
    Image:	nginx:1.17.8-alpine  # 移轉後版本
    Port:	80/TCP
    Host Port:	0/TCP
    Limits:
      cpu:	200m
      memory:	128Mi
    Environment:	<none>
    Mounts:	<none>
  Volumes:	<none>

若要回滾到先前的版本，使用 kubectl rollout undo deployment my-nginx --to-revision=1

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

再次查看history，可看到revision為3的回滾紀錄

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$ kubectl rollout history deployment my-nginx

deployment.apps/my-nginx
REVISION  CHANGE-CAUSE
2         kubectl create --filename=nginx.deployment.yml --save-config=true --record=true
3         kubectl create --filename=nginx.deployment.yml --save-config=true --record=true

回滾完畢後，使用 kubectl describe deploy [name] 查看

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$ kubectl describe deploy my-nginx

Name:                   my-nginx
Namespace:              default
CreationTimestamp:      Thu, 29 Oct 2020 22:10:47 +0800
Labels:                 app=my-nginx
Annotations:            deployment.kubernetes.io/revision: 3
                        kubectl.kubernetes.io/last-applied-configuration:
                          {"apiVersion":"apps/v1","kind":"Deployment","metadata":{"annotations":{},"labels":{"app":"my-nginx"},"name":"my-nginx","namespace":"defaul...
                        kubernetes.io/change-cause: kubectl create --filename=nginx.deployment.yml --save-config=true --record=true
Selector:               app=my-nginx
Replicas:               4 desired | 4 updated | 4 total | 4 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        1
RollingUpdateStrategy:  1 max unavailable, 1 max surge
Pod Template:
  Labels:  app=my-nginx
  Containers:
   my-nginx:
    Image:      nginx:1.16.1-alpine    # 可看到已經回滾為原本的版本！
    Port:       80/TCP
    Host Port:  0/TCP
    Limits:
      cpu:        200m
      memory:     128Mi
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>

  ...

參考

Pluralsight: Kubernetes for Developers: Deploying Your Code
https://app.pluralsight.com/library/courses/kubernetes-developers-deploying-code/table-of-contents

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