Architecture Pattern: CQRS

Command and Query Responsibility Segregation provides excellent decoupling for shared data at a nominal price of higher latency for latest data. It fits very well in micro service architecture for cases of data sharing among services where one service is a reader and another a writer.

Implementation

Suppose there are two serviceA & B that need to share a database. We do not want to create a DB dependency. So, we can create two DBs and purpose them for writing only and reading only.

Service A always writes to its DB. And after every write it sends and event to a pub/sub. B is subscribed to the pub/sub. B get all write events from the pub/sub and update its DB. All clients of service B always read B’s DB.