Service Over Servers

Servers are ephemeral, you don't care about them. You only care about the service as a whole.

If a single server dies, it should be of no big concern to you. This is where the real benefit of AWS comes in compared to using physical servers yourself. Normally if a physical server dies, there's panic. With AWS, you don't care, because auto-scaling will give you a fresh new instance soon anyway. Netflix have taken this several steps further with their simian army, where they have things like Chaos Monkey, which will kill random instances in production (they also have Chaos Gorilla to kill AZs and I've heard rumour of a Chaos Kong to kill regions...). The point is that servers will fail, but this shouldn't matter in your application.