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Solving the Dual-Write Problem: Implementing the Transactional Outbox Pattern

  It’s the distributed system nightmare every backend engineer encounters eventually. Your application successfully commits a record to the database (e.g., a new user sign-up). Immediately after, it attempts to publish an event to Apache Kafka to trigger downstream services (e.g., send a welcome email). But the network blips. The message broker is unreachable. The application throws an error, but the database transaction is already committed. You now have a  dual-write inconsistency . The user exists in your primary database, but the rest of your microservices architecture has no idea. The system is out of sync, and manual reconciliation is painful. This guide details how to solve this strictly using the  Transactional Outbox Pattern  with PostgreSQL, Kafka, and Debezium. The Anatomy of the Dual-Write Problem Before fixing it, we must understand why the naive approach fails. In a monolithic architecture, you might rely on a single ACID transaction. In microservices, ...