Configuring the external URL for GitLab
In order for GitLab to display correct repository clone links to your users
it needs to know the URL under which it is reached by your users, e.g.
http://gitlab.example.com. Add or edit the following line in
/etc/gitlab/gitlab.rb:
external_url "http://gitlab.example.com"
Run sudo gitlab-ctl reconfigure for the change to take effect.
then restart GitLab: sudo gitlab-ctl restart
Refers:
https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/doc/settings/configuration.md#configuring-the-external-url-for-gitlab
https://forum.gitlab.com/t/change-domain-name/1174/2