There are two main options for installing a Gitlab server. Both are fairly convenient, and which you choose is largely dependent on how you want to run your server. You can either spin up a Docker container, which is better for servers running other services. Alternatively, you can run Gitlab directly on Ubuntu. It sort of takes over a lot of ports, so this method is best for dedicated servers.
This is a companion discussion topic for the original entry at https://linuxconfig.org/how-to-install-gitlab-on-ubuntu-18-04-bionic-beaver