I am running Gitlab in Docker (using official images), how would you go with upgrading from version 12.10 without losing any data? I am using volumes for Gitlab data.
Please read through the upgrade notes for 13.0 as there are some important changes like PG11 being a minimum requirement.
As for the actual upgrade, you should be able to follow the standard process outlined here since you are persisting your data outside the container: https://docs.gitlab.com/omnibus/docker/#update
As for the actual upgrade, you should be able to follow the standard process outlined here since you are persisting your data outside the container: https://docs.gitlab.com/omnibus/docker/#update