proxy_pass, dynamic ports upstream

[mahhy]

I have a requirement to be able to map a portion of a request URI to a port
on a set of upstream servers.  I'm hoping nginx will be able to solve this
for me, but so far no luck.

Request:
http://example.com/2201/reg/106903/0?something=here&somemore=stuff

Needs to be proxied to:
http://10.11.12.13:2201/reg/106903/0?something=here&somemore=stuff

So the 1st portion of the URI is used as the upstreams port.  However I'm
having difficulty with this when I attempt to combine it with a set of
upstream servers.  The below configuration results in the error "no resolver
defined to resolve engines".

If I specify the upstream as " proxy_pass  http://10.11.12.13:$1/$2/?$args;
" (and change nothing else) the below configuration works... however it's
not being load balanced obviously.

Basically, can I load balance and use dynamic ports?


Configuration:

upstream engines  {
  server 10.11.12.13;
  server 10.11.12.14;
}

server {
  listen       *:80;

  access_log  /var/log/nginx/engines.access.log  main;
  error_log   /var/log/nginx/engines.error.log debug;

  location ~/([0-9]*)/ {
    rewrite ^/([0-9]*)/(.*)$ $2 break;
    proxy_pass  http://engines:$1/$2/?$args;
    proxy_next_upstream error timeout invalid_header http_500 http_502
http_503 http_504;
    proxy_redirect off;
    proxy_buffering on;
    proxy_set_header        Host            $http_host;
    proxy_set_header        X-Real-IP       $remote_addr;
    proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
  }
}

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,232849,232849#msg-232849