Update a Deployment image in Kubernetes

Use the following functionality if you have atleast a 1.15 version

kubectl rollout restart deployment/deployment-name

Read more about it here kubectl rollout restart

when not changing the container image name or tag you would just scale your application to 0 and back to the original size with sth like:

kubectl scale --replicas=0 deployment application
kubectl scale --replicas=1 deployment application

As mentioned in the comments already ImagePullPolicy: Always is then required in your configuration.

When changing the image I found this to be the most straight forward way to update the

kubectl set image deployment/application app-container=$IMAGE

Not changing the image has the downsite that you'll have nothing to fall back to in case of problems. Therefore I'd not suggest to use this outside of a development environment.

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Edit: small bonus - keeping the scale in sync before and after could look sth. like:

replica_spec=$(kubectl get deployment/applicatiom -o jsonpath='{.spec.replicas}')
kubectl scale --replicas=0 deployment application
kubectl scale --replicas=$replica_spec deployment application

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Cheers