Part 2: Sagas, Fan-In, and Correlation: Solving the Hard Problems of Eventual Consistency in EDA
Choosing event-driven architecture means choosing eventual consistency. The only question is how well you manage it. When payment succeeds but inventory reservation fails, do you refund automatically or let a customer stare at a half-completed order? This guide covers Saga compensation patterns, the callback topic debate (and why it’s really async RPC over event infrastructure), fan-out vs fan-in complexity, and three concrete approaches to multi-topic correlation — with production code in Python, Java, and AWS.