NOTE
3.1 RabbitMQ Routing and Usage
RabbitMQ exchanges, bindings, queues, direct/fanout/topic routing, work queues, acknowledgements, prefetch, and dead-letter patterns.
This is a historical learning note and may contain outdated or incomplete understanding.
1. Data Flow
Publishers normally send messages to an exchange. Bindings route matching messages from the exchange into queues. Consumers receive from queues.
The default exchange can route directly to a queue by queue name.
2. Exchange Types
Direct
Route when the message routing key exactly matches a binding key.
Fanout
Broadcast to every queue bound to the exchange, ignoring the routing key.
Topic
Route using wildcard patterns in routing keys, useful for hierarchical event categories such as:
order.created.eu
order.cancelled.usHeaders
Routing can also be based on message headers rather than the routing key.
3. Work Queues
Multiple consumers can compete for messages from one queue. RabbitMQ distributes deliveries among active consumers subject to channel prefetch/credit and availability.
Configure prefetch so a slow worker does not accumulate an excessive number of unacked messages.
4. Acknowledgements
Use manual acknowledgements when work must not be considered complete until processing succeeds.
Failures can lead to redelivery, so consumers should be idempotent.
5. Dead Lettering
Rejected, expired, or otherwise dead-lettered messages can be routed to another exchange/queue for bounded retry, debugging, or manual remediation.
Avoid infinite immediate requeue loops.