How to Configure many servers to work as one?

We have a free hosting trail service that usually runs for three months and it has over 5000 accounts. We had purchase a large server but the server clashed due to mis-configuration of /dev/root. The dev/root space was set at 256 GB which was too small and neither mysql or backup could be stored on that space. We want to separate the big server into multiple small servers. The only challenge is on managing many servers. We prefer a setup that can work like Amazon where by we can add servers and increase on server capacity on demand. Can I use DRBD or Gluster FS to merge multiple servers to work as one big cloud server? Alternatively we can work with master - slave setup where by;

• A change on master server is passed down to all servers especially multi-php and tweaks
• DNS to be ns1.domain.com and ns1.domain.com for all servers.
• Shared Redis or Varnish.

We will be happy to find a solution on this problem. Thank you.