I have a little forum, themooster.net, based on Discourse that I had not upgraded in a couple of months.
I clicked “Update” in the “Admin” recommendation to upgrade, and it said I had to do the upgrade at the shell prompt instead, and gave me three lines to run:
cd /var/discourse git pull ./launcher rebuild app
I ran those three commands. The “rebuild app” failed initially, because I didn’t have 5 GByte free on my little linode box, so I added more disk space and the “rebuild app” seemed to complete ok.
But the site didn’t come back up.
I looked around, rebooted, still not coming up, looked around a bit more.
Seems that the frontend nginx is coming up ok, but when I try to access my forum over the web, like a normal user, I get a " 502 Bad Gateway" error from the nginx frontend.
The file “/var/discourse/shared/standalone/log/var-log/postgres/current” is filled with errors such as:
2021-04-17 13:54:37.785 UTC  FATAL: database files are incompatible with server
2021-04-17 13:54:37.785 UTC  DETAIL: The data directory was initialized by PostgreSQL version 13, which is not compatible with this version 10.12 (Debian 10.12-2.pgdg100+1).
I have good backups of the forum in my directory:
Now what should I do?