I don't know much about securing a server. I've heard of iptables, but I've never used it (maybe that's not what I need?).
So right now my goal is to have a main webserver, and a separate database and memcached server (unless you think I should just have one webserver and one server with mysql and memcached?).
At any rate, is there a way on the server that is not the web server (e.g. the mysql / memcached servers) to basically not accept any traffic or anything from anywhere but the webserver? What's the best way to do this? And is this recommended?
Also, I'm using rackspace's cloud servers. They include something called an "internal ip address". I'm assuming that's what I should use because it's probably faster than and "external ip address".