Ubuntu Server, used their standard install instructions, no docker. So far all their upgrades went without any problems at all, including major version bumps.

Ubuntu Server, used their standard install instructions, no docker. So far all their upgrades went without any problems at all, including major version bumps. As for running the server, I cannot recall any bigger problem I had, Zulip runs in our org for more than 5 years. Backups are also pretty easy to setup.