Micro services: shared library vs code duplication

Question

Similar questions were asked a few times, but as every use-case can be different I thought it worth to ask it again with the specific case I\'m facing with. So, we are devel

Answer 1

Of course there is DRY rule in programming. But, as Sam Newman said in his book "Building Microservice": Don't Repeat Yourself inside one microservice.

Common entities: Let's look at your example with ResponseC. Imagine that something in ServiceB has changed so now one of the field from the response have changed - now you have to update each service that uses this shared library, even if the service don't need this changed field. If you had the ResponseA, ResponseB and ResponseC for each service, you didn't had to update each service with the new dependency.

Common logic: Basically the same rules are applied here. However it's common to use some third party libraries for common microservices issues like time-outs and retries. What else I can suggest is to look at service mesh implementation like istio and linkerd. Service mesh will give the possibility to these issue to the infrastructure layer so you can focus on writing business logic.