Producer Patterns

Producers decide whether an event-driven system becomes a useful fact-distribution model or a noisy side channel. The producer is where business meaning starts, where publication timing is chosen, and where one of the hardest reliability problems appears: keeping state change and event publication aligned. Chapter 5 focuses on those responsibilities directly.

Read the lessons in order. The first explains domain events as stable business facts. The second covers notification events and the callback trade-offs they introduce. The third explores event-carried state transfer as a way to improve consumer autonomy. The fourth turns to the transactional outbox pattern, which is one of the most practical ways to reduce divergence between committed state and emitted events.

If a producer in your system “just publishes something” after local work completes, but nobody can explain whether the message is a domain fact, a notification hint, a full state transfer, or a reliably published contract, Chapter 5 is where that producer model needs to become explicit.

In this section

• Domain Events
  A practical lesson on domain events as meaningful business facts, including how they differ from technical messages and why stable semantics matter to consumers.
• Notification Events
  A practical lesson on lightweight notification events, their strengths in producer simplicity, and the callback-coupling risks they introduce downstream.
• Event-Carried State Transfer
  A practical lesson on event-carried state transfer, how it improves consumer autonomy, and the producer-side cost it introduces in payload and schema responsibility.
• The Transactional Outbox Pattern
  A practical lesson on the transactional outbox pattern for keeping local state changes and event publication aligned without unsafe dual writes.