server_name  www.xxx.com;
...
location / {
    proxy_redirect off;
    proxy_pass http://ip[原服务器ip];
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    index index.html index.htm;
}