Deploying on Nginx and Mongrel--what is http://mongrel?

Hello Group,

I've got my Rails app deployed as a Mongrel cluster behind an Nginx
reverse proxy. It's working great except for one small issue: if I
have code that does a redirect_to <named route>, the browser is
redirecting to http://mongrel. What I'd like to have it direct to is
"http://<my domain name>/<url>". Does that make sense?

Here's my Nginx config file:

    upstream mongrel {
        server 127.0.0.1:9000;
        server 127.0.0.1:9001;
        server 127.0.0.1:9002;
    }

<snip>

    server {
        listen 80;
        server_name <my domain name>;
        root <my deployment path>;

<snip>

        location / {
            proxy_pass http://mongrel;
            proxy_redirect off;
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For
$proxy_add_x_forwarded_for;
        }