PM2 is enhancing capability of NodeJs by utilizing configured cores, it doesn’t change the single-threaded nature of NodeJs app. It is using IPC on the backend for communication and data transfer between the processes running on multiple cores. I covered these details in part-I about clustering.

Elastic beanstalk also takes care of infra resources management but if an instance has more than single-core, it won’t change the nature of NodeJs. If clustering is not involved than other cores seems to be a kind of waste.

I would advise using PM2 if an instance has more than single-core, that’s my opinion but kindly try a stress testing with/without PM2, and share the result.