Exchanges & Routing

Routing is the whole job of an exchange

An exchange stores nothing. Its one job is routing: take a published message and decide which queues get a copy. How it decides is set by the exchange’s type. Learn the four types and you can express almost any message-flow topology.

What this module covers

Lesson	The exchange decides by…
Direct exchange	An exact routing key match
Fanout exchange	Nothing — it copies to every bound queue
Topic exchange	A pattern match on a dotted routing key
Headers & choosing	Message headers, plus a guide to picking a type

The four types at a glance

flowchart TB
  msg["message
routing key: order.created"] --> direct["direct
match key exactly"]
  msg --> fanout["fanout
ignore key, copy to all"]
  msg --> topic["topic
match key pattern"]
  msg --> headers["headers
match on header values"]

How each exchange type routes the same message

The mental model to carry through this module:

• A message always carries a routing key (a string like order.created) and optional headers.
• Each binding from an exchange to a queue may carry a binding key (or pattern, or header conditions).
• The exchange type is the rule that compares the message against the bindings to pick queues.

Everything else — pub/sub, work distribution, event filtering — is just a choice of exchange type plus some bindings.

🐇 The one-line takeaway

An exchange routes; it never stores. Its type is the routing rule: direct matches a routing key exactly, fanout copies to every bound queue, topic matches a key pattern, and headers matches on header values. Pick the type, add bindings, and you’ve designed your message flow.

What is the single job of an exchange?

To store messages until consumers are ready To route a published message to the right queues To acknowledge messages on behalf of consumers To compress message bodies

What determines how an exchange routes a message?

The size of the message The exchange type (direct, fanout, topic, or headers) The consumer that will read it The order it was published in

Which exchange type ignores the routing key entirely?

direct topic fanout headers

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