I have an Apache web application which is serving ~2k Requests Per Minute. The current infrastructure includes two servers, one acting as Apache + database, and the second one just database.
I'm trying to evaluate the added value from moving the Apache to its own server and/or maybe even a couple of small instances and a load balancer.
How can I perform such evaluation? I'm using New Relic for server monitoring and seeing most (~70%) of the app server time spent is in PHP.
It is a pretty standard n+1 architecture you are describing. It will certainly provide you with many scaling options going forward.
Many of our services run on similar format
This format also benefits from providing the ability for a Apache instance to be taken down for updates and allowing the site to remain live (you must consider how you manage data changes).
You mentioned a small instance - if you are in AWS - you can use their elastic load balancer in front of your Apache instances - it works extremely well. They also offer MySQL DBs as a service too.
New relic has plugins for all aspects so you can monitor load across each element of the infrastructure.
There are also many options available to scale MySQL - we find read only slaves very effective for our applications.
