[gatestone]

Immutable means "something that can not be changed" and is used somewhat strangely here. Better be more concrete:

Yes, we want to have declarative configurations and idempotent "terraform apply".

Yes we want to have containers and subsystems with no persistent state, and careful architecture for persistent storage volumes and database services.

And please remember to say "prevent_destroy", "ignore_changes" etc for that persistent data where appropriate. And remember that the automation that creates your system in one command will be able to destroy it in one command, if you say so.