Advice on an odd networking problem

[Pete French]

> Who returns 503?
>
> Is it the Apache that returns 503, nginx, or does the connection to nginx
> never complete?

Its the load balancer - the sequence should be this:

load balancer -> apache -> nginx localhost -> uwsgi

but the load balancer is returning a 503 as it cannot complete
the connection to the apache process..

> If the scripts see failures then do they always report the type of failure
> on stderr where it should show up in Apache's error_log?

On the webserver machine nothing appears out of the ordinary.
theres nothing in the logs - the requests never seem to make it as far
as the machine. It is as if it runs out of spacw to accept connections
(somaxconn is 1024 on these machines)

> I'm trying to figure out if it is Apache or nginx that is the origin of
> the problem. Are you running out of processes available to CGI scripts
> maybe?

No, that is fine - the load is very low. It just looks
as if the connectio to apache never happens. We have tried
replacing the load balancer (have tried nginx and ound there) same
result for both, so its something on the webserver side.

*scratches head*

-pete.