I run a similar setup on the Rackspace Cloud (1 DB + 1 Web) for multiple sites. I use iptables to lock down all non-essential ports, I setup MySQL to accept con

I run a similar setup on the Rackspace Cloud (1 DB + 1 Web) for multiple sites. I use iptables to lock down all non-essential ports, I setup MySQL to accept connections over the private IP and, frankly, that's it. (FWIW, I use Moonshine on my Rails app to keep the config easy/repeatable.)