NGinx multi-docker-container reverse proxy config

nginx.conf

events {
    worker_connections  1024;
}
http {
    resolver 127.0.0.11;
    server {
        server_name  ~^(?<ctrn>[^\.]+)-(qa|dev)\.;
        location / {
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            set $pp "http://$ctrn";
            proxy_pass $pp;
        }
    }
    server {
        server_name  ~^(?<ctrn>[^\.]+);
        location / {
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            set $pp "http://$ctrn";
            proxy_pass $pp;
        }
    }
}