In the current state of infrastructure, an accepted definition of "immutable infrastructure" is that:

1. You deploy a completely fresh instance/container, instead of in-place updates 2. You don't actively push changes on a running instance/container

Of course you might have stuff written to disk, such as logs, temp files, etc. But it should be non-essential data, and potentially pushed to a central place in near real-time.

Interesting. How would you do that if your deployment is, say, a couple of new tables in a 50TB Oracle database?

It only works with stateless resources.

There's no point in trying to manage a database or similar resources this way.