nginx forward proxy - 502 bad gateway

[mex]

> 
> This server is behind a cisco firewall with port 8080 open. Where is
> the
> problem?
> 
> The line:
> 
> proxy_pass http://$http_host$uri$is_args$args;
> 
> has problem with firewalls? or it is something else?
> 


are you able to connect to $http_host from that second server,
maybe via lynx/w3m?
$ telnet $http_host 8080 

and then 

GET / 

additionally, can you execute the following on that
server to check if you're able to connect to your resolver:

$ nslookup $http_host 8.8.8.8

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,237162,237164#msg-237164