Update the image of a pod without changing the IP address of the pod - Elastic Container Instance

When you update a pod to troubleshoot issues or to improve features of the pod, you may need to modify the image of the pod. During this process, the IP address of the pod cannot be changed to ensure business continuity. This topic describes how to use kubectl commands to update the container image of a pod and keep the IP address of the pod unchanged.

Prerequisites

The image to be updated is prepared and uploaded to an image repository.

Procedure

The following example describes how to use kubectl commands to update a container image from nginx:1.7.9 to nginx:1.9.6 and keep the IP address of the pod that runs NGINX unchanged.

Note

To perform the operations in the following example, make sure that an Internet NAT gateway is created and SNAT is configured for the VPC to which the cluster belongs. This way, the image can be pulled over the Internet.

Create an Elastic Container Instance-based pod.

kubectl create -f nginx.yaml

The following code provides an example of the content of nginx.yaml. The container image used is nginx:1.7.9.

apiVersion: v1
kind: Pod
metadata:
  name: nginx
  namespace: default
  labels:
    alibabacloud.com/eci: "true" 
spec:
  containers:
  - image: nginx:1.7.9
    imagePullPolicy: Always
    name: nginx

Query the information of the pod.

Query the IP address of the pod.

kubectl get pod/nginx -n default -o wide

The following sample output shows that the IP address of the pod is 172.16.22.193.

NAME    READY   STATUS    RESTARTS   AGE    IP              NODE                           NOMINATED NODE   READINESS GATES
nginx   1/1     Running   0          5m5s   172.16.22.193   virtual-kubelet-cn-beijing-e   <none>           <none>

Query the image tag of the pod.
```
kubectl get pod/nginx -n default -o=custom-columns='IMAGE:spec.containers[*].image'
```
The following sample output shows that the container image of the pod is nginx:1.7.9.
```
IMAGE
nginx:1.7.9
```

Use one of the following methods to update the container image:
- kubectl patch
  Run the kubectl command to modify the image tag.
```
kubectl patch pod nginx -p '{"spec":{"containers":[{"name": "nginx","image": "nginx:1.9.6"}]}}'
```
- kubectl edit
  Run the kubectl edit command to edit the pod and modify the image tag.
```
kubectl edit pod/nginx -o yaml 
```
- kubectl apply
  Open the nginx.yaml configuration file of the pod, modify the image tag, and then run the kubectl apply command to redeploy the pod.
```
kubectl apply -f nginx.yaml 
```

View the information of the pod after you update the image.

Query the IP address of the pod.

kubectl get pod/nginx -n default -o wide

The following sample output shows that the IP address of the pod is 172.16.22.193, which is the same as the IP address of the pod before you update the image.

NAME    READY   STATUS    RESTARTS   AGE   IP              NODE                           NOMINATED NODE   READINESS GATES
nginx   1/1     Running   1          19m   172.16.22.193   virtual-kubelet-cn-beijing-e   <none>           <none>

Query the image tag of the pod.
```
kubectl get pod/nginx -n default -o=custom-columns='IMAGE:spec.containers[*].image'
```
The following sample output shows that the container image of the pod is updated to nginx:1.9.6.
```
IMAGE
nginx:1.9.6
```