04 - Rolling Updates and Rollbacks

Q: Inspect the deployment and identify the number of PODs deployed by it

Ans: 4

$ kubectl get deploy                                              

$ kubectl describe deployment | grep -i Desired        

Replicas: 4 desired | 4 updated | 4 total | 4 available | 0 unavailable

Q: Inspect the deployment and identify the current strategy

$ kubectl describe deployment frontend | grep -i StrategyType             

Ans: StrategyType: RollingUpdate

Q: If you were to upgrade the application now what would happen?

Ans: PODs are upgraded few at a time

Q: Let us try that. Upgrade the application by setting the image on the deployment to `kodekloud/webapp-color:v2`. 

Do not delete and re-create the deployment. Only set the new image name for the existing deployment.

• Deployment Name: frontend
• Deployment Image: kodekloud/webapp-color:v2

Run the command `kubectl edit deployment frontend` and modify the image to `kodekloud/webapp-color:v2`. 

Next, save and exit. The pods should be recreated with the new image.

方法一：

$ kubectl edit deployment frontend                

方法二：

$ kubectl set image deployment frontend simple-webapp=kodekloud/webapp-color:v2     

過程如下：

原本建立的：kodekloud/webapp-color:v1

RollingUpdate：把原本的 pods 一個一個地慢慢替換，實現 Zero Downtime

所有 Pods 更新完成：kodekloud/webapp-color:v2

Q: Up to how many PODs can be down for upgrade at a time

Consider the current strategy settings and number of PODs - 4

Look at the Max Unavailable value under RollingUpdateStrategy in deployment details

Ans: maxUnavailable: 25% x 4 pods = 1

strategy.rollingUpdate.maxUnavailable: 25%

Q: Change the deployment strategy to `Recreate`

Delete and re-create the deployment if necessary. Only update the strategy type for the existing deployment.

• Deployment Name: frontend
• Deployment Image: kodekloud/webapp-color:v2
• Strategy: Recreate

$ kubectl edit deployment frontend                  

```

apiVersion: apps/v1

kind: Deployment

metadata:

  name: frontend

  namespace: default

spec:

  replicas: 4

  selector:

    matchLabels:

      name: webapp

  strategy:

    type: Recreate           # 修改 (原本 strategy.RollingUpdate 相關設定要記得刪除)

  template:

    metadata:

      labels:

        name: webapp

    spec:

      containers:

      - image: kodekloud/webapp-color:v2

        name: simple-webapp

        ports:

        - containerPort: 8080

          protocol: TCP

```

結論

• Recreate：把原本的 pods 全部刪除，接著全部重新建立，有 downtime（502 Bad Gateway）
• RollingUpdate：把原本的 pods 一個一個地慢慢替換，實現 Zero Downtime

$ kubectl set image --help                 

Usage:

  kubectl set image (-f FILENAME | TYPE NAME) CONTAINER_NAME_1=CONTAINER_IMAGE_1

... CONTAINER_NAME_N=CONTAINER_IMAGE_N [options]