I agree, but at least in many cases, containers aren't the immutability mechanism. E.g., MicroOS seems to rely on btrfs snapshots--all changes are dropped on re

I agree, but at least in many cases, containers aren't the immutability mechanism. E.g., MicroOS seems to rely on btrfs snapshots--all changes are dropped on reboot and the system starts from a fresh factory state. Your application could be containerized or it could be a package pulled from the distro repository and managed by systemd.