[IanCal]

> Single instance. To spin up an instance, you need another computer.

I think you can do this with cloudformation, having it respond to the size of a work queue, however:

> Maybe someone just doesn't have time, yet, to learn/configure/maintain spinning up an instance for limited times.

This is why I can't answer the question above for certain, I got about that far in documentation and went off to find a simpler solution (for me, tutum: https://www.tutum.co/ )