location / {
    proxy_pass              http://127.0.0.1:3000/;
    proxy_redirect          off;
    proxy_set_header        X-Real-IP       $remote_addr;
    proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
}

参考：

https://www.vpser.net/manage/linux-vps-nginx-reverse-proxy.html