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Pattern: Application publishes events

Also known as

Transaction outbox pattern


A service typically need to atomically update the database and publish messages/events. For example, perhaps it uses the Saga pattern. In order to be reliable, each step of a saga must atomically update the database and publish messages/events. Alternatively, it might use the Domain event pattern, perhaps to implement CQRS. In either case, it is not viable to use a distributed transaction that spans the database and the message broker to atomically update the database and publish messages/events.


How to reliably/atomically update the database and publish messages/events.


  • 2PC is not an option


The application that uses a relational database inserts messages/events into an outbox table (e.g. MESSAGE) as part of the local transaction. An application that uses a NoSQL database appends the messages/events to attribute of the record (e.g. document or item) being updated. A separate Message Relay process publishes the events inserted into database to a message broker.

Result context

This pattern has the following benefits:

  • High level domain events
  • No 2PC

This pattern has the following drawbacks:

  • Potentially error prone since the developer might forget to publish the message/event after updating the database.

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