Single responsibility per service

The single responsibility principle is one of the principles defined as part of the SOLID design pattern. It states that a unit should only have one responsibility.

It implies that a unit, either a class, a function, or a service, should have only one responsibility. At no point do two units share one responsibility, or one unit perform more than one responsibility. A unit with more than one responsibility indicates tight coupling:

As shown in the preceding diagram, Customer, Product, and Order are different functions of an e-commerce application. Rather than building all of them into one application, it is better to have three different services, each responsible for exactly one business function, so that changes to one responsibility will not impair the others. In the preceding scenario, Customer, Product, and Order were treated as three independent microservices.