All boxes need to be upgraded to bullseye. this milestone tracks related issues and larger projects that can't easily be automated.

As part of the OKR 2022 Q1/Q2 plan, we have set the following key results in this objective:

1. all machines are upgraded to bullseye
2. migrate to Prometheus for monitoring (team#29864 (closed)) or upgrade to Inciga 2
3. upgrade to Mailman 3 or retire it in favor of Discourse (!) (team#40471)

Upgrade procedures and progress are also documented in the howto/upgrades/bullseye wiki page. In particular, a post mortem is available there.

Note that the initial due date (2022-07-01) was pushed back by a full year since other, higher priority work took over the last few servers to migrate in the meantime. We did audit the servers to make sure they were covered by Debian LTS at least.

The plan to upgrade everything in batches was set in TPA-RFC-20: bullseye upgrades.