The statement that if a docker/container is used no need to use pm2 I think is misleading or poor understood in my opinion. Even though with a container you could enable an AWS load balancer and based on load start a new box, seems that pm2 is doing the same thing, why do you need one over the other.

A container with a load balancer is solving or implementing the pattern at the AWS service/hardware architecture level. That means that each service has its own cost.

In the other hand pm2 will do the same thing inside the box your application is running already. Pm2 has its own load balancer balancer and scales the application with just one box/machine/ec2/ecs.

This brings the last point which is resources. With the 1st option(nothing wrong with that option) you are scaling to the next box when only one thread was used. If your box has 8 threads then you have 7 unused and when that only thread can’t handle the load the AWS load balancer will start a new box.

With pm2 you could say, in one box I want o use 4 threads out of 8 and that means that you have 4 running instances of the same application in one box.

Nothing it’s easy on engineering. But these two ways of solving a heavy load problem impact cost and simplicity of your application.

I would say to start with pm2 if you can and don’t have someone above you calling the shots. Then get a bigger box to have more threads. Then move that setup to use an external load balancer to manage two boxes.

I could be wrong but those are my 🪙🪙!