Date: 2020-05-25
Accepted (lazy consensus) & implemented
Read Event Bus ADR for context.
Given several James servers, we need them to share a common EventBus.
This:
group mailbox listners.Provide a distributed implementation of the EventBus leveraging RabbitMQ.
Events are emitted to a single Exchange.
Each group will have a corresponding queue, bound to the main exchange, with a default routing key. Each eventBus will consume this queue and execute the relevant listener, ensuring at least once execution at the cluster level.
Retries are managed via a dedicated exchange for each group: as we need to count retries, the message headers need to be altered and we cannot rely on rabbitMQ build in retries. Each time the execution fails locally, a new event is emitted via the dedicated exchange, and the original event is acknowledged.
Each eventBus will have a dedicated exclusive queue, bound to the main exchange with the registrationKeys used by local notification mailboxListeners (to only receive the corresponding subset of events). Errors are not retried for notifications, failures are not persisted within DeadLetter, achieving at most once event delivery.
The implementation of the the distributed EventBus suffers from the following flows:
The following enhancement have furthermore been contributed: