Попробуйте так:
location / {
proxy_pass http://backend;
proxy_redirect default;
proxy_set_header Host $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?21,212486,212491#msg-212491