Most metrics are coming from a diagnostic call on the server being tested (memory use etc) with throughput data (request per second etc) coming from the program

Most metrics are coming from a diagnostic call on the server being tested (memory use etc) with throughput data (request per second etc) coming from the program testing it. There is only limited data regarding the system collected - memory use of the JVM primarily. Each test instance starts fresh on 2 ec2 instances, one for the performance test package which replays abstracted logs and one for the server being tested. Each test instance saves the data for its test run, which I grab before shutting down the instance. On the assumption that each instance is clean at start of test, I have not considered much how performance of the system itself impacts the tests - but perhaps I should revisit this. Most of our stuff is custom code for a number of reasons, the biggest external library being HttpClient. I'm not sure how other people have solved this particular problem, I just got to the point that clean EC2 instances were generating pretty comparable data and then set to putting out fires in the code (: