How do I force Kubernetes to re-pull an image?

In Kubernetes, there are several methods to force re-pulling images:

1. Change the Image Tag

By default, Kubernetes will not re-pull images if the deployment uses a specific version tag (e.g., myimage:1.0) unless the image tag is modified. To force re-pulling, update the image tag—such as from myimage:1.0 to myimage:1.1 or using the latest tag—and ensure imagePullPolicy is set to Always in the deployment configuration.

For example:

yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  template:
    spec:
      containers:
      - name: myapp
        image: myimage:latest
        imagePullPolicy: Always

2. Use imagePullPolicy: Always

Setting imagePullPolicy to Always in the deployment YAML file ensures Kubernetes attempts to re-pull the image whenever a new Pod is launched.

yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  template:
    spec:
      containers:
      - name: myapp
        image: myimage:latest
        imagePullPolicy: Always

3. Manually Delete Existing Pods

Deleting existing Pods manually triggers Kubernetes to rebuild them based on the imagePullPolicy setting. If imagePullPolicy is configured as Always, it will re-pull the image.

You can use the kubectl command-line tool to delete Pods:

bash
kubectl delete pods --selector=app=myapp

4. Use Rolling Updates

For applications deployed as Deployments requiring an image update to a new version, employ a rolling update strategy. This involves modifying the Deployment's image tag and allowing Kubernetes to replace old Pods incrementally according to your defined strategy.

For instance, update the Deployment's image:

bash
kubectl set image deployment/myapp myapp=myimage:1.1

Example

Suppose you have a running application using the image version myapp:v1. To update to myapp:v2, first modify the image name in your Deployment configuration file and set imagePullPolicy to Always. Then apply the changes with kubectl apply -f deployment.yaml. Kubernetes will replace old Pods with the new version incrementally via the rolling update strategy.

These methods can be selected and applied based on specific scenarios and requirements to ensure Kubernetes runs the application with the latest image.