People love talking about their state being immutable when in 99.9% of the cases it is not.
Here's a simple test: if your runtime container infrastructure is immutable, you should be able to run your container with a file system being read-only. If you cannot do that, then you do not have an immutable infrastructure and hence you will need need something to manage the state. Ignoring it is akin to kicking housekeeping tasks to some point in future and hoping that before you get buried under the multi-year backlog of tiny corner cases before your entire product is replaced with something else.
Here's a simple test: if your runtime container infrastructure is immutable, you should be able to run your container with a file system being read-only. If you cannot do that, then you do not have an immutable infrastructure and hence you will need need something to manage the state. Ignoring it is akin to kicking housekeeping tasks to some point in future and hoping that before you get buried under the multi-year backlog of tiny corner cases before your entire product is replaced with something else.