The scalability of a service describes how expensive it is to operate as it grows. The more users access the service, the more expensive it becomes—but how much more expensive? The answer to that question is the service’s scalability. As we design services, we want them to be as scalable as possible so that their growth results in higher revenue out of proportion with the increase in expenses.
It is possible—in fact, quite easy—to design the opposite kind of service, where growth results in greater expense growth than revenue, and which therefore “hits a wall” and can no longer profitably grow.
How do we design services that scale?