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design-patternsmicroservicesmessagingmessagebroker

Need for transacional outbox pattern on microservices

I see a recommendation for using the transactional outbox pattern (https://microservices.io/patterns/data/transactional-outbox.html) for scenarios in which a message should be published to a broker after some change in the database, so it can be "ACID". My question is: why not put the message publish inside the transaction like this?

try {
   beginTransaction()
   saveStuff()
   publishMessage() 
   commitTransaction()
} catch() {
   rollbackTransaction()
}

This way, whenever the message publish fails, the transaction will be rolled back. I see only one issue: you may not want to rollback the transaction when the message publish fails, trying again later. Are there other issues with this approach?

Solution

  • The publishMessage can work (the message is sent) but the commitTransaction might fail (eg lost connection to the database or the application crashes after sending message and before calling commit)