A simple docker-compose.yml that sets up GitLab-CE with almost all the optional services disabled at start.
This can reduce CPU and RAM usage A LOT, in testing this example uses less than 2GB of RAM.
This should be deployed with a reverse proxy like Traefik or Caddy and the containers hostname and external_url set correctly.
Alternatively configure GitLab to provide HTTPS by itself.
This is not meant to be a copy/paste and run foolproof way to run GitLab, it should serve as a example on how to slim it down.