Actually, we still can't scale easily on demand. Let's say you get 2x the traffic. Sure, your front-end instances in the cloud can scale to 2x the capacity, but

Actually, we still can't scale easily on demand. Let's say you get 2x the traffic. Sure, your front-end instances in the cloud can scale to 2x the capacity, but that just moves the bottleneck over to your database. And then you noticed that scaling an Amazon RDS database to a larger instance requires downtime...