So far, we have created only one EC2 instance for the web application MightyTrousers. As the popularity of the app increases, a single server can't handle the load properly anymore. We could scale vertically by increasing the instance size, but it would still leave us with a single server that handles all the critical traffic. In a cloud world, you should assume that absolutely every machine you have can be gone at any moment. You should be prepared for worst case scenarios: a distributed denial-of-service (DDoS) attack putting your cluster on its knees, an earthquake destroying the whole data center, an internal AWS outage, and many others.
Thus, not only as a way to scale the infrastructure, but also to make the application ...
