There is one more dimension to this problem. It is how engineers are going to be interacting with the model which includes ability to understand, predict and co

There is one more dimension to this problem. It is how engineers are going to be interacting with the model which includes ability to understand, predict and configure it. For a mechanism to scale server farm, it cannot be too surprising to engineers that work on it. They need to be able to understand what it does more or less to be able to figure out what is going and deal with problems. This is even more important in corner cases. What is going to be startup behavior? What happens when a large number of servers goes down? Etc. These behaviors can be very rarely encountered but engineers must be able to predict and reason about them.