Using HttpMapModule with proxy_pass got 502

[amozz]

Hi everyone,

My project needs to route http request to different host with different
domain name. I deployed HttpMapModule and proxy_pass, and the related
nginx.conf segment is following:

http {
   map $http_host $backend_servers {
        app.example.com       localdomain1; #if changed to ip, it's ok
        default                       localdomain2;
   }
   
   server {
        listen              80;
        server_name    localhost;
        location /{
             proxy_pass http://$backend_servers;
        }
   .......
   }

When I send the requet uri as http://app.example.com, the result is 502
error. But if I changed the maping value as IP address not domain name, it
worked with no problem. And if I change the proxy_pass item directly to
http://localdomain1, it also worked as normal.

Does the proxy_pass + http_map_module not refer to DNS look? or is there any
other point wrong in the nginx.conf ?  

Thanks for any suggestion.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,235450,235450#msg-235450