When does nginx return a Bad gateway (502)?

[fastcatch]

Thank you.

BTW: having googled it for different expressions I've found that it is a
well known issue and that it has nothing to do with nginx or the Rails app
itself. Unicorn in and of itself can neither be blamed (albeit IMHO there
should be some official documentation on this issue, esp. since nginx is the
preferred/"official" web server for unicorn).  It looks like a socket
backlog setting issue to be handled at OS level but I'm still unsure if
that's a resolution or not.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,237573,237590#msg-237590