...
It could be, the full unredacted error_log entries might have more details.
I would test with curl/wget on the proxy and make sure the backend is
reachable. If curl/wget don't work, the proxy server isn't going to
work.
SOLVED
The reverse proxy setup was fine. My problem was my Raku listener program on the backend was tied to localhost instead of the public IP address. (Solved by Geoffrey Broadwell on IRC #cro.)
Now I need the reverse proxy to handle multiple virtual hosts on the same IP using SNI.
I'll attempt that in another email.
Thank you very much, Eric.
Cheers!
-Tom