RabbitMQ Exchange Types: Direct, Fanout, Topic, and Headers

Every message in RabbitMQ passes through an exchange before reaching a queue — the exchange is the routing engine, and the four exchange types differ in how they decide which queues receive each message.

Direct exchange — exact key matching:

• Publish with routing key order.created and only queues bound with that exact key receive the message — the workhorse for task queues and point-to-point messaging
• The default exchange is a nameless direct exchange where every queue is auto-bound using its name as the routing key, which is why beginner tutorials work without explicit exchange declarations
• Direct exchanges can also fan out: bind multiple queues with the same key, and each gets a copy — surprising for those who assume direct is always point-to-point

Fanout exchange — unconditional broadcast:

• Ignores the routing key entirely and broadcasts to every bound queue, making it the right choice for cache invalidation and notification fan-out where every subscriber needs every message
• A common debugging trap: publishing to a fanout while expecting filtered delivery because you set a routing key — the key is silently ignored

Topic exchange — wildcard pattern routing:

• Uses dot-delimited routing keys with wildcards: * matches exactly one word, # matches zero or more; audit.# catches audit.payment.failed, audit.user.login, everything under audit
• The most frequent topic exchange bug: confusing * and # — audit.* would NOT match audit.payment.failed because that's two words after the dot

Headers exchange:

• Routes by message header attributes with AND/OR logic via x-match: all or x-match: any — powerful for multi-dimensional routing but slower than key matching due to per-message header inspection

I recommend starting with direct for simple task distribution, moving to topic when you need pattern-based routing, and treating headers as a last resort where the overhead is justified.