So far we have a Varnish droplet to serve as a load balancer to 2 Nginx droplets. And, we use asw s3 to store all the uploaded media files. Varnish droplet direct all logged in users(wp-admin) to the first Nginx droplet (we call it master droplet). The problem now if we made change to master droplet(for example: code deployment, new sub site registration), it doesn't sync to the other Nignx droplet. What is the best way to keep those Nginx in sync?