Upgrading to buster
You should first upgrade to 11.11.8 version before you can install newer versions.
Update /etc/apt/sources.list and change stretch to buster and add anew entry for buster-fasttrack,
deb http://deb.debian.org/debian buster contrib main deb http://security.debian.org/ buster/updates contrib main deb https://people.debian.org/~praveen/gitlab buster-backports contrib main deb https://people.debian.org/~praveen/gitlab buster-fasttrack contrib main deb http://deb.debian.org/debian buster-backports contrib main
Add a workaround for yarn not finding har-validator if you got such an error,
# ln -s /usr/share/nodejs/har-validator/ /var/lib/gitlab/.node_modules/
Now update gitlab
# apt -t buster-backports install gitlab ruby-asciidoctor=1.5.8-1 gitaly=1.42.5+debian-1~bpo10+1 bundler nodejs
If you got some errors during "Running final rake tasks and tweaks..." step, you may have to remove some obsolete configuration files (especially if you installed gitlab from stretch for the first time),
rm /usr/share/gitlab/config/initializers/0_license.rb rm /usr/share/gitlab/config/initializers/0_thread_cache.rb rm /usr/share/gitlab/config/initializers/active_record_query_cache.rb rm /usr/share/gitlab/config/initializers/elastic_client_setup.rb rm /usr/share/gitlab/config/initializers/geo.rb rm /usr/share/gitlab/config/initializers/load_balancing.rb rm /usr/share/gitlab/config/initializers/transaction_metrics.rb
Stretch Backports (upgrade to buster)
Gitlab 11.4.9 is available in stretch-backports (still affected by some security issues, many security releases behind).
Gitlab 11.5.10 is available for stretch-backports via personal repo of gitlab maintainer (many security releases behind) from https://people.debian.org/~praveen/gitlab
Add to /etc/apt/sources.list
deb https://people.debian.org/~praveen/gitlab stretch-backports contrib main deb http://deb.debian.org/debian stretch-backports contrib main
Add repo signing key as trusted,
# wget https://people.debian.org/~praveen/gitlab/praveen.key.asc # apt-key add praveen.key.asc
Now install gitlab,
# apt -t stretch-backports install gitlab
It is recommended to upgrade to buster to receive security updates (see above).
Note: Remove unnecessary packages after upgrade (remove ruby-bootsnap if you see strange load errors).
# apt remove rails npm ruby-bootsnap
Stretch (upgrade to stretch-backports and then to buster)
Gitlab 8.13.11 was available in stretch, but it was not receiving any security updates and was removed in a point release. So it is recommended to update to newer versions from stretch-backports (see above).
# apt install gitlab
It is recommended to upgrade to stretch-backports and then to buster to receive security updates.