Share data between microservices

Question

I work on a microservices architecture and I want to solve a small data sharing problem (I don't know if is the right word).

Example :

I have one user service and is DB that stores email, username, password...

I have another service and his database that work with the user data for generate documents with the user informations.

Which is the best way for the second service for accessing to the user data ? Replicate user data (Just if is required for his job) for her in is database ?

Answer 1

I don't know the design of the whole system, but I would let the user microservice send an event when a user is created, updated or deleted. All other microservices which are interested in this event can extract the necessary user data they need.

By using microservices a redundant data cannot be avoided, but each microservice has different view on the data.

Your user microservice may see the user more as identity with complete user data (e.g id, password, first name, last name, email, address, organization, etc.) On the other hand, your document generation microservice may see the user as receiver of the document and do not need all user data.

Answer 2

There is the caveat consultants answer of 'it depends'. Everyone has a different description of what microservices are, but for me they are small independently deployable services that do one thing well (i generally subscribe to fowlers definition of microsevices).

Actually I don't have a problem with microservices sharing storage (be it databases, blob storage etc.) as long as the microservices fall within the same 'service' boundary. What i mean by service boundary is a logical grouping of small services all collaborating to achieve some goal or business capability. For me its this logical grouping which forms the 'service' as viewed from outside the team. One service 'the user service' is often made up of many small microservices.

For example you might have a 'User' service that consists of a number of microservices. One to capture interest from a website and store it in a DB, one used by the website to process address changes, one to run a timed job and issue events to other services in the system.

But you would not want the Document Generation (reporting service?) reading and writing from the User DB, in this case (like Stavreva said) event communication between services would be the way to go.

Only you with your business domain knowledge can decide if two microservices belong within this same service, one tip is to look at the business capability that the microservice is contributing towards.