"Understand the dual-write problem and how transactional outbox patterns, idempotent consumers, retries, and recovery improve event reliability."

A common backend operation looks simple:

Update database + Publish event

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The difficulty appears when one succeeds and the other fails.

This is a problem I consider when designing backend systems that coordinate database transactions with asynchronous processing, external services, or other independently operating components.

The challenge is not simply how to save a record or publish a message.

It is how to ensure that the system remains consistent when failures occur between those operations.

The dual-write problem

Suppose the application does:

1. Save order 2.…