How to Setup a Node Balancer with a Postgres Database

I'm new to server administration and really more of a software developer than an sysadmin, so sorry if this is too much of a newb questions:

I understand the concept of node balancers and multiple server instances running simultaneously, and I also understand that they have to share a common database if anything is going to work properly. What I don't get is how to best go about actually setting up something like this? I was wondering if anyone could direct me to a good tutorial or give me some advice directly.

If it's important, I'm using Ruby Rails applications on Ubuntu 12.04 instances with a Postgres DB.