When Discourse is being upgraded the main site is showing HTTP Status 500 exception. That's because of blogs integration. Maybe something can be done to now have this happening during the upgrades.
While at it, maybe something can also be done from the Discourse side to show "Upgrading" page instead of an error while upgrading it. Although it seems that this involves rebooting its docker container and then nothing is working from it. Probably more complex solution would be to do something on the site side then.