Hello,
It's a nifty thing called Load Balancing.
We are seeing an urgent rise in this very technology.
You can either use hardware based balancing or either used software based using HA Proxy or Nginx.
PS : We are coming out with a Load Balancing Panel soon, PM me if you want to be on our BETA Invite list.
It is based on our forked edition of Nginx called PraMOD WebServer.