How to update pods if version hasn't changed?
The main problem here is, that from a Kubernetes point-of-view nothing has changed to your deployment. So nothing gets updated.

The best solution here would be, that you add something to your image tag, like the git short hash, for example. The your update will just work. Also you will make your deployments re-creatable, when you do it this way.

If you really want to keep it the way it is, you could add some other information to the deployment, that changes on each deployment, but is not used, like an annotation. But I would not recommend that, since I saw this leading to strange behavior with old pods no being shutdown.

On a side note: The imagePullPolicy is just evaluated, when there is change to your deployment. So basically this flag says: If you do deploy something (e.g. bc there is a new deployment), no matter if you have the image already locally, reload it from the registry.