Monitor performance of application cluster

How to monitor the performance of my application cluster? Is it possible to have aggregated performance data of my application cluster?

You can install the APM agent on each application server and specify the same application name in configurations to group all server instances under one application in APM web client. 

Basically each app server must have its own agent jar and conf files. All agents can have same name and these will be grouped in the APM tab. Please note that both aggregated data and individual app server data can be viewed separately.