How Big Should a Service Be?

1. The Wrong Question, Asked Constantly

"How big should a microservice be?" comes up constantly, and it is the wrong question, because it has no numeric answer. People give a size anyway: "a few hundred lines," "two weeks to rewrite," "one entity." Every one of those answers rests on a wrong belief about what the word micro measures. Micro measures responsibility, not code.

The right size comes from two constraints, one from each direction:

• Lower bound: a service must be able to do its job on its own data. It should not have to ask other services for help on every request