I am not using it with immutable config, so the only thing flatcar is doing is it has an A and a B partition for /usr that it switches between on updates (such that it can always rollback to the last working system).

I only used ignition for the initial setup, after that I just ssh in to the machine and change systemd services via /etc/systemd/system (such as added new mounts, using systemd unit’s for running docker containers etc.)

The idea is that all software you need to run except for systemd and some utilities (more or less what is in busybox) are run in containers, which i think was the same deal with RancerOS.