My preliminary setup is like this.
Two QuadCore 8GB servers running debian 6, with php and apache,
One QuadCore 16GB server running debian 6, with mysql
My plan is to have one 8Gb server to act as a proxy server, using vertx java to handle connections. I will let vertx use HttpClient to send web requests to the second 8GB server. This would have apache installed and use php to deliver any information that it gets from the mysql server on the third, 16GB server.
The main reason I want this setup is to have things separated, so the "proxy" will be the only way to access the system, as the other two server will only be reachable from the local network.
I can have the vertx proxy handle 5000+ concurrent connections, but, I don't know how to configure apache to handle all the requests coming from the proxy. Php will connect over mysqli with persistent connection pool of 500-800 connections, the mysql server seems not to have any issues on this part.
In previous projects, the apache part was always causing issues, no matter how I set it up. I might not fully understand how to setup apache, since normally apache should handle many concurrent connections, but it does seem to now.