After being so happy about all the services that I brought up last weekend, I forgot to do one thing: rebooting. Today I rebooted for some reason and the containers didn’t came up again.
I had weird errors: port 80 was blocked by a docker-proxy process even though all was down, file systems in docker could only be mounted read-only, …
Quite a time debugging later I figured out that there were two docker services running! One installed via apt, the other via snap. — After uninstalling the snap-version of docker, I rebooted and — everything was fine again!