I have a GitLab (v 11.0.3) installed on a Debian 8.11 jessie server. As you can imagine this is a pretty old installation.
Updating these seem a bit tricky - there are many intermediate versions.
My question is: do you thing migrating the repositories to a newly deployed server (like Debian 10 or Ubuntu 20.04) and a newly installed GitLab (higher/last version) would work?
Or the only way is to update everything: server + GitLab?
It would be already great if I can at least move it to a newly deployed server, with the same Git version.
Once you are on 13.3.9, you could then make a Gitlab backup. Then install a new version of Debian 10 or Ubuntu 20.04 and then install on this Gitlab 13.3.9 for Ubuntu 20.04. Copy the /etc/gitlab/gitlab.rb from your old installation along with the gitlab-secrets.json file to the new server and run gitlab-ctl reconfigure. Then copy the backup from /var/opt/gitlab/backups from your old server to the same location on the new server and run the restore. More info on backup/restore here: Back up and restore GitLab | GitLab