Microservices and the Single Responsibility Principle

 The Single Responsibility Principle (SRP) is the first software design principle in the well-known Bob Martin's SOLID acronym.  The SRP is a guiding principle to design classes and corresponding functions that should only change for the same reasons.  That is, the functionality of the class should be implemented to satisfy a given actor, as in a use case UML diagram.

Similarly, there is another principle called the Common Closure Principle CCP) that says that classes of similar behavior should be combined in the same component or package.  This principle can be clearly seen in the Java API packages (or any other well-structured programming language API).

From the architecture point of view, there is a concept called "Context Boundary" borrowed from the Domain Driven Design (DDD) book of Eric Evans.

Both the CCP and the Context Boundary can be thought of as higher-level design principles that are derived from the SRP.  And microservices should focus on following the same guidelines of SRP here.  That is, a microservice should be focused on a smaller subset of a given business domain.  As a matter of fact, when designing a Microservice Architecture, we should look at our system from a domain-driven design perspective.  That is, delineate the different content boundaries first.  And then, designing the microservices afterwards.

Therefore, the SRP is a principle that applies to designing a microservices architecture.