If there have multiple instances of ProcessOutBoxJob, The events may be processed in many times. about sample-dotnet-core-cqrs-api

[kgrzybek]

Hi @zh6335901,

If you have many Outbox processors you can't process events in parallel because the order of events matters. It will be a problem for your subscriber if he would receive OrderCanceled event and then OrderCrated event.

Even you will solve the problem with processing one event many times using some locking mechanism on the table or more advanced solution like using Rabbit MQ which has "round-robin" by default, the order of published events would be incorrect.

So you should have only one processing instance working at the same time. If you want to have multiple instances, other instances should be inactive. You can achieve this using Single Consumer Rabbit MQ feature: https://www.rabbitmq.com/consumers.html#single-active-consumer As documentation says:

Consuming with only one consumer is useful when messages must be consumed and processed in the same order they arrive in the queue.

[zh6335901]

Hi @kgrzybek
You are right. The order of events is important. But if the Outbox processors only have one instance, I am worried about it would be lost the high available.
Maybe i need find a solution that multiple instances but only one working at the same time.

[zh6335901]

Thank you for your answer. And your aritcles is help me out