Mastering Direct, Topic, and Fanout Exchanges in AMQP

Exchange Overview

Producer sends messages to an Exchange, which routes them to one or more Queues based on Routing Key and Binding Key. Three exchange types are supported: Direct, Topic, and Fanout.

Direct Exchange

Routing rule : matches when Binding Key equals Routing Key.

Use case : differentiate messages sent to the same Exchange.

Example : Direct Exchange bound to Queue A with binding key img.create and to Queue B with img.log. Producer sends messages with corresponding routing keys, and they are delivered to the matching queues.

Bind Direct Exchange to queues:

Binding key for Queue A: img.create Binding key for Queue B: img.log Producer sends messages:

Message A routing key: img.create Message B routing key: img.log Exchange routes messages where Binding Key = Routing Key:

Message A goes to Queue A.

Message B goes to Queue B.

Topic Exchange

Routing rule : uses wildcard matching. * matches a single word, # matches zero or more words separated by dots.

Use case : differentiate messages by pattern.

Example : Queue A bound with files.cn.hz.#, Queue B with files.cn.*.store. Producer sends messages with routing keys files.cn.hz, files.cn.hz.store, files.cn.sz.store. Routing follows wildcard rules.

Bind Topic Exchange to queues:

Queue A binding key: files.cn.hz.# Queue B binding key: files.cn.*.store Producer sends messages:

Message A routing key: files.cn.hz Message B routing key: files.cn.hz.store Message C routing key: files.cn.sz.store Exchange routes:

Message A → Queue A.

Message B → Queue A and Queue B.

Message C → Queue B.

Fanout Exchange

Routing rule : ignores routing and binding keys; broadcasts messages to all bound queues.

Use case : broadcast scenarios.

Example : Queues A, B, C bound with any key; producer sends a message with any routing key; all queues receive the message.

Bind Fanout Exchange to queues A, B, C (binding keys arbitrary).

Producer sends a message (routing key arbitrary).

Exchange delivers the message to all bound queues.