Date: 2020-04-03
Accepted (lazy consensus) & implemented
James allows asynchronous processing for mailbox events via MailboxListener. This processing is abstracted by the EventBus.
If the processing of an event via a mailbox listener fails, it is retried, until it succeeds. If a maxRetries parameter is exceeded, the event is stored in deadLetter and no further processing is attended.
The administrator can then look at the content of deadLetter to diagnose processing issues and schedule a reDelivery in order to retry their processing via webAdmin APIs.
However no such capabilities are supported upon dispatching the event on the eventbus. A failed dispatch will result in message loss.
More information about this component can be found in ADR 0036.
Upon dispatch failure, the eventBus should save events in dead letter using a dedicated group.
Reprocessing this group an admin can re-trigger these events dispatch.
In order to ensure auto healing, James will periodically check the corresponding group in deadLetter is empty. If not a re-dispatching of these events will be attempted.
In distributed James Guice project an administrator have a way to be eventually consistent upon rabbitMQ failure.