A Simple utility to monitor web application performance

My system setup is like: Application A takes requests from outside world and communicates with the backend REST apis. REST api also communicates with mysql database.

My requirement is to have a tool from which I can just monitor the resource usage and may be the performance of the web server. I want to have graphs for the resource usage which means I need historical data otherwise I would have just used the windows task manager to see the resource usage.

This means I do not need any load generator(that will be done by the Application A) just a resource monitor.

I googled and found tools like appdynamics, Nagios, munin but not sure if they are what I need. I haven't done performance testing earlier so there's lot of confusion.

Just looking for some guidance.

Thanks