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RabbitMQ — Middle

At middle level, focus on this question:

How do you choose between direct, topic, fanout, and headers exchange types for a given routing requirement?

Prerequisite: junior.md.

The four exchange types

flowchart LR Direct["DIRECT: exact\nrouting_key match"] --> DirectUse["Use: simple\none-to-one routing\n(task queues)"] Topic["TOPIC: pattern match\n(orders.*.completed)"] --> TopicUse["Use: hierarchical\nevent categories"] Fanout["FANOUT: ignores\nrouting key entirely,\nsends to ALL bound\nqueues"] --> FanoutUse["Use: broadcast to\nevery subscriber\n(pub/sub)"] Headers["HEADERS: match on\nmessage HEADER\nattributes, not\nrouting key"] --> HeadersUse["Use: routing based\non multiple, non-\nhierarchical attributes"]
# Topic exchange: pattern-based routing
channel.exchange_declare(exchange="events", exchange_type="topic")
channel.queue_bind(exchange="events", queue="order_events", routing_key="orders.*")
channel.queue_bind(exchange="events", queue="all_completed", routing_key="*.completed")

# A message published with routing_key="orders.completed" matches BOTH bindings
  • Direct: exact string match on routing key — the simplest, most predictable routing, ideal for classic queue/worker-pool patterns.
  • Topic: wildcard pattern matching (* for one segment, # for zero-or-more) — ideal for hierarchical event categorization (orders.created, orders.completed, users.signup).
  • Fanout: ignores the routing key entirely, delivers to every bound queue — the direct implementation of pub/sub broadcast from Message Queues — middle.
  • Headers: matches on arbitrary message header key-value pairs instead of a single routing key string — useful when routing depends on multiple independent attributes that don't naturally form a hierarchy.

🎓 Takeaway: exchange type is the single configuration choice that determines your routing semantics — pick based on whether you need exact matching, hierarchical pattern matching, broadcast-to-everyone, or multi-attribute matching, not by defaulting to whichever type you used last time.

Test yourself

  1. Why would a topic exchange with routing key orders.*.completed NOT match a message published with routing key orders.completed (missing the middle segment)? (Hint: think about what * matches versus #.)
  2. Why is fanout the right choice for "notify every subscriber of this event," rather than direct or topic?
  3. Design the exchange type and routing key scheme for a system that needs to route messages based on both "region" and "priority" independently.

Continue to senior.md.