2.2. Consumer-driven messaging

AMQP uses consumer-driven messaging. In traditional point-to-point messaging a message producer publishes messages to a queue. The message producer is responsible for knowing which queue will receive the messages. The queue in this model is an endpoint for a single consumer. In the traditional publish-subscribe model, the queue can be an endpoint for multiple consumers, who can receive individual copies of the messages sent to queue, or can share access to unique messages, taking them in a round-robin fashion. In AMQP all of these styles of messaging are supported: sending directly to a known queue for a single consumer or for multiple consumers, allowing consumers to browse their own copies of messages on the queue or mandating that they share access to unique instances of messages in a round-robin fashion.

AMQP implements these patterns using a flexible architecture where senders send their messages to an exchange. The exchange distributes the message to the queues subscribed to the exchange. This allows all the previously described models, and also provides the opportunity for message consumers to drive the conversation. Message producing applications do not need to be aware of new applications that come online and are interested in the message producer's messages. Message consumers can create queues and bind them to exchanges.

AMQP has a number of exchange types that support different distribution mechanisms. When subscribing to an exchange, message consumers can bind their queue with parameters that act as a filter on messages. By choosing which exchange type to use, and using binding keys to filter the messages from that exchange, you can build extremely flexible, fast, and extensible messaging systems using AMQP.