1576ee279f
Currently a 404 is returned for a misconfigured or unavailable upstream server. Since that's a server error it should be a 5xx instead; a 404 is confusing when used as a forward proxy and might even be harmful when used as a reverse proxy. It is debatable if another 5xx code might be better; the misconfigured situation might better be a 500 whereas the connection issue could be a 503 instead (as used eg. in haproxy).