route different proxy based on subdomain request in nginx

create a virtual host for each

server {
  server_name sub1.example.com;
  location / {
    proxy_pass http://127.0.0.1:xxxx;
  }
}
server {
  server_name sub2.example.com;
  location / {
    proxy_pass http://127.0.0.1:xxxx;
  }
}

And go on, change the port number to match the right port.