Topic exchange (pattern matching) in RabbitMQ - Step-by-Step Execution

Process Flow - Topic exchange (pattern matching)

Producer sends message with routing key

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Topic Exchange receives message

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Exchange compares routing key with binding keys

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Match?

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Route to queues

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Consumers receive messages from queues

Messages are sent with routing keys to a topic exchange, which routes them to queues whose binding keys match the routing key pattern.

Execution Sample

RabbitMQ

1. Producer sends message with routing key: "stock.usd.nyse"
2. Topic exchange has bindings:
   - Queue A: binding key "stock.*.*"
   - Queue B: binding key "stock.usd.#"
3. Exchange routes message based on pattern match

This example shows how a message with routing key "stock.usd.nyse" is routed to queues with matching binding keys using topic exchange pattern matching.

Process Table

Step	Routing Key	Binding Key	Match Result	Action	Queues Routed
1	stock.usd.nyse	stock.*.*	Yes	Route message	Queue A
2	stock.usd.nyse	stock.usd.#	Yes	Route message	Queue B
3	stock.usd.nyse	stock.eur.#	No	Discard for this binding	-
4	stock.usd.nyse	stock.#	Yes	Route message	Queue C (if exists)
5	stock.usd.nyse	other.binding	No	Discard for this binding	-
6	-	-	-	Routing complete	Queues A, B, (C if exists)

💡 All bindings checked; message routed to all matching queues.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
Routing Key	-	stock.usd.nyse	stock.usd.nyse	stock.usd.nyse	stock.usd.nyse
Binding Key	-	stock.*.*	stock.usd.#	stock.eur.#	-
Match Result	-	Yes	Yes	No	-
Queues Routed	-	Queue A	Queue A, Queue B	Queue A, Queue B	Queue A, Queue B

Key Moments - 3 Insights

Why does the binding key 'stock.*.*' match 'stock.usd.nyse'?

Because '*' matches exactly one word in the routing key, so 'stock.*.*' matches 'stock.usd.nyse' where 'usd' and 'nyse' are the two words matched by '*'. See execution_table row 1.

Why does 'stock.usd.#' match the routing key?

'#' matches zero or more words, so 'stock.usd.#' matches any routing key starting with 'stock.usd', including 'stock.usd.nyse'. See execution_table row 2.

What happens if no binding keys match the routing key?

The message is discarded or dead-lettered because no queues are bound with matching patterns. See execution_table row 5.

Visual Quiz - 3 Questions

Look at the execution table, which binding key does NOT match the routing key 'stock.usd.nyse'?

A stock.eur.#

B stock.usd.#

C stock.*.*

D stock.#

💡 Hint

Check the 'Match Result' column in execution_table rows 1-5.

At which step does the message get routed to Queue B?

A Step 1

B Step 2

C Step 3

D Step 5

💡 Hint

Look at the 'Queues Routed' column in execution_table for when Queue B appears.

If the routing key was 'stock.eur.london', which binding key would match?

A stock.usd.#

B stock.eur.#

C stock.*.*

D other.binding

💡 Hint

Refer to how '#' matches zero or more words in binding keys from key_moments.

Concept Snapshot

Topic Exchange routes messages by matching routing keys to binding keys using patterns.
'*' matches exactly one word.
'#' matches zero or more words.
Messages route to all queues with matching binding keys.
Non-matching messages are discarded.

Full Transcript

In RabbitMQ, a topic exchange routes messages based on pattern matching between the message's routing key and the binding keys of queues. The routing key is a string with words separated by dots. Binding keys can include '*' to match exactly one word and '#' to match zero or more words. When a message arrives, the exchange compares the routing key to each binding key. If they match, the message is routed to the corresponding queue. If no binding keys match, the message is discarded. For example, a routing key 'stock.usd.nyse' matches binding keys like 'stock.*.*' and 'stock.usd.#'. This allows flexible routing based on patterns.