I am evaluating and trying to estimate hosting costs for an existing Java based web application and am currently trying to determine the most effective hosting solution. In looking at Amazon EC2 hosting and am trying to get an apples to apples comparison versus what we have established now with our parent companies data center.
Our current setup is non-virtualized. We have 3 servers:
An under utilized public-facing Apache web server, acting as reverse-proxy setup.
and 2 identical application servers, load-balanced, and behind a firewall.
Let's ignore the database.
My question is if such a 3 server setup is practical in comparison to simply having a single large instance? What I am getting at is being since I have to pay for the bandwidth usage, will network communication between my instances on their own subnet count against my bandwidth usage?
If so then the monolithic super instance would probably make more financial sense than say many smaller load balanced application servers behind their own firewall.