An interesting way to work around this would be to have the ability to scale with mixed instance types. For example, your base application runs with t2.micro.

An interesting way to work around this would be to have the ability to scale with mixed instance types. For example, your base application runs with t2.micro. As soon as traffic starts going up, you launch additional medium/large instances. The load balancer would have to understand this also, and do weighted routing (ideally based on app server loads) so the first micro instance doesn't handle the same volume of traffic as the rest. I've never seen a setup like this before, and frankly, part of me wonders whether the savings would be worth the effort of building it in the first place (vs just running with medium instances, or just scaling to dozens of micros to handle the load, or just using serverless).