The dual-write problem occurs when an application writes data to a database record and then publishes an event to a message broker, and one of these operations fails. This can lead to inconsistencies where an order exists in the database but no downstream systems are notified, or vice-versa, causing issues like ghost orders and chargebacks. A transactional outbox pattern, facilitated by Symfony Messenger, provides a robust solution.The core idea is to insert the event into a database table (the outbox) within the same transaction as the primary data write. This ensures atomicity: both the order and the event record are committed together or not at all. Symfony Messenger's Doctrine transport can be configured to act as this outbox table. By routing events to a Doctrine transport, the INSERT operation for the event message is included in the existing database transaction.After the transaction commits, a separate process, typically messenger:consume, acts as a relay. This relay reads messages from the outbox table and dispatches them to their intended destinations, such as RabbitMQ. This decouples the event dispatch from the initial request handling, making the system resilient to broker outages or temporary restarts. The messenger:consume command uses SELECT FOR UPDATE SKIP LOCKED to allow multiple workers to process messages from the outbox concurrently without processing duplicates.Crucially, the outbox pattern guarantees at-least-once delivery, meaning handlers must be idempotent to safely handle potential message replays. This can be achieved by storing a stable event ID and checking a processed events table before executing any side effects. By routing events to a Doctrine transport and using messenger:consume as the relay, applications can achieve reliable event delivery without requiring custom infrastructure. This approach keeps infrastructure concerns at the edge, allowing the domain to focus on business logic and enabling easier future changes to message transports.