Sauerbraten: Cube 2 server via Docker
Read this blog post for details, but tl;dr copy server-init.tmpl.cfg to server-init.cfg and make any changes you want, then run:
$ docker-compose build
$ docker-compose up -d
The docker-compose.yml file uses a volume to mount the server-init.cfg file in your current directory into the proper container path, modify as you see fit.
After a couple minutes, your server should show up in the server list in the game. If it doesn't check the logs with docker-compose logs and ensure that your network settings are correct (by default, ports 28785 and 28786 via both TCP and UDP).