Why would nginx 0.7.6 is drop requests randomly

[Maxim Dounin]

Hello!

On Wed, Mar 06, 2013 at 01:23:28AM +0100, Arman Mirk wrote:

> I notice our server is rapidly responding 500 errors for random pages.
> Our setup is pretty basic. We are running Nginx 0.7.6 with Unicorn and a
> Rails app on a Ubuntu 10.4 server.
> 
> What ever the problem, it doesn't seem to happen at the application
> level since Unicorn logs don't contain any errors. Next we looked at
> Nginx's error logs and there doesn't seem to be any entries. Yes when we
> monitor the Nginx's access log we notice rapid 500 error responses on
> random pages.
> 
> This is really strange since our server isn't under a lot of load. It
> uses a 4 core Linode instance and we have 4 Nginx worker processes.
> 
> Could someone people point us to the right direction?

If it indeed happens in nginx, I would suppose it's some 
configuration problem, something like rewrite loop, or proxy loop, 
or something similar.  It should have reasons logged to error log 
though.  To make sure it's indeed happens in nginx, and not 
returned by your application, you may try logging $upstream_status 
variable, see docs here:

http://nginx.org/en/docs/http/ngx_http_upstream_module.html

You may also use debug log to check what goes wrong in details, 
see here:

http://nginx.org/en/docs/debugging_log.html

But in any case 0.7.6 is a 5 years old development version, and 
you may want to upgrade.

-- 
Maxim Dounin
http://nginx.org/en/donation.html