Topic exchange (pattern matching) in RabbitMQ - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Routing key matching with topic exchange

Given a topic exchange with a binding key stock.*.nyse, which routing key will cause a message to be delivered to the queue?

A stock.tech.nyse

B stock.nyse

C stock.tech.nyse.extra

D stock.nyse.tech

💡 Hint

Remember that * matches exactly one word in the routing key.

The binding key stock.*.nyse matches routing keys with exactly three words where the middle word can be anything. Option A matches this pattern. Option A has only two words, C has four words, and D has the words in the wrong order.

🧠 Conceptual

intermediate

Understanding the '#' wildcard in topic exchanges

What does the # wildcard represent in a RabbitMQ topic exchange binding key?

A Matches only the last word in the routing key

B Matches exactly one word in the routing key

C Matches only the first word in the routing key

D Matches zero or more words in the routing key

💡 Hint

Think about how many words # can match.

The # wildcard matches zero or more words separated by dots in the routing key. It allows flexible matching of multiple words or none.

🔀 Workflow

advanced

Configuring multiple bindings for selective message routing

You want to route messages with routing keys log.error.system and log.error.application to a queue named ErrorLogs. Which binding keys should you use on the topic exchange to achieve this?

A log.error.*

B log.*.error

C log.#.error

D *.error.*

💡 Hint

Consider the position of the wildcard and the routing key words.

The binding key log.error.* matches routing keys starting with log.error. followed by exactly one word. Both log.error.system and log.error.application match this pattern.

❓ Troubleshoot

advanced

Why messages are not routed as expected

A queue is bound to a topic exchange with the binding key sensor.#. Messages with routing key sensor are not delivered to the queue. What is the most likely reason?

A The queue is not properly bound to the exchange

B The binding key 'sensor.#' only matches routing keys with exactly two words

C The routing key must have at least one word after 'sensor' to match 'sensor.#'

D The '#' wildcard does not match zero words, only one or more

💡 Hint

Check how the '#' wildcard behaves with zero words.

The binding key sensor.# matches routing keys starting with 'sensor' followed by zero or more words separated by dots. However, the routing key 'sensor' has only one word and no dot, so it does not match the pattern which expects 'sensor.' followed by words.

✅ Best Practice

expert

Optimizing topic exchange bindings for performance

Which practice helps improve performance when using topic exchanges with many bindings and high message throughput?

A Use fanout exchanges instead of topic exchanges for all routing needs

B Use more specific binding keys with fewer wildcards to reduce routing overhead

C Use only '#' wildcards in all bindings for maximum flexibility

D Bind all queues with the same binding key to simplify routing

💡 Hint

Think about how routing keys and bindings affect message routing speed.

More specific binding keys with fewer wildcards reduce the number of matches the exchange must check, improving routing performance. Overusing wildcards like '#' can cause more routing overhead.

Practice

1. What is the main purpose of a topic exchange in RabbitMQ?

easy

A. To broadcast messages to all queues regardless of routing keys

B. To store messages until consumers are ready

C. To route messages based on pattern matching of routing keys

D. To encrypt messages before sending

Solution

1. Step 1: Understand the role of exchanges in RabbitMQ

   Exchanges route messages to queues based on rules. Topic exchanges use patterns in routing keys.

2. Step 2: Identify the unique feature of topic exchanges

   Topic exchanges route messages by matching routing keys with patterns containing * and # wildcards.

3. Final Answer:

   To route messages based on pattern matching of routing keys -> Option C

4. Quick Check:

   Topic exchange = pattern matching routing [OK]

Hint: Topic exchange uses wildcards to match routing keys [OK]

Common Mistakes:

• Confusing topic exchange with fanout exchange
• Thinking topic exchange stores messages
• Assuming topic exchange encrypts messages

2. Which of the following is the correct syntax to bind a queue named logs to a topic exchange named topic_logs with routing key pattern kern.* using RabbitMQ CLI?

easy

A. rabbitmqadmin declare binding source=topic_logs destination=logs routing_key=kern.*

B. rabbitmqctl bind queue=logs exchange=topic_logs routing_key=kern.*

C. rabbitmqadmin bind queue=logs exchange=topic_logs routing_key=kern.*

D. rabbitmqctl declare binding source=topic_logs destination=logs routing_key=kern.*

Solution

1. Step 1: Identify the correct RabbitMQ CLI tool for binding

   Binding queues to exchanges is done with rabbitmqadmin declare binding, not rabbitmqctl.

2. Step 2: Check the correct parameters for binding

   The correct parameters are source for exchange, destination for queue, and routing_key for pattern.

3. Final Answer:

   rabbitmqadmin declare binding source=topic_logs destination=logs routing_key=kern.* -> Option A

4. Quick Check:

   Use rabbitmqadmin declare binding with source, destination, routing_key [OK]

Hint: Use rabbitmqadmin declare binding with source and destination [OK]

Common Mistakes:

• Using rabbitmqctl instead of rabbitmqadmin for binding
• Swapping source and destination parameters
• Omitting routing_key parameter

3. Given a topic exchange with a queue bound using the routing key pattern *.orange.*, which routing keys will deliver messages to this queue?

medium

A. quick.orange.rabbit, orange

B. orange.rabbit, quick.orange

C. quick.orange, orange.lazy.rabbit

D. quick.orange.rabbit, lazy.orange.elephant

Solution

1. Step 1: Understand the pattern *.orange.*

   The pattern means exactly three words separated by dots, with 'orange' as the middle word. The * matches exactly one word.

2. Step 2: Check each routing key against the pattern

   quick.orange.rabbit, lazy.orange.elephant keys: 'quick.orange.rabbit' and 'lazy.orange.elephant' both have three words with 'orange' in the middle, so they match.

3. Final Answer:

   quick.orange.rabbit, lazy.orange.elephant -> Option D

4. Quick Check:

   Pattern *.orange.* matches three-word keys with orange in middle [OK]

Hint: Count words; * matches one word, # matches zero or more [OK]

Common Mistakes:

• Assuming * matches zero or multiple words
• Ignoring word count in routing key
• Confusing * with # wildcard

4. You have a queue bound to a topic exchange with the routing key pattern stock.#. Messages with routing key stock.us.nyse are not delivered to the queue. What is the most likely cause?

medium

A. The exchange type is not set to topic

B. The routing key pattern stock.# does not match stock.us.nyse

C. The queue is not bound correctly to the exchange

D. The message was published with an empty routing key

Solution

1. Step 1: Verify the exchange type

   The pattern stock.# matches routing keys starting with 'stock' followed by zero or more words. If messages are not delivered, the exchange might not be a topic exchange.

2. Step 2: Check other possible causes

   Binding and routing key pattern are correct. If the exchange is not topic type, pattern matching won't work.

3. Final Answer:

   The exchange type is not set to topic -> Option A

4. Quick Check:

   Topic exchange required for pattern matching [OK]

Hint: Ensure exchange type is topic for pattern matching [OK]

Common Mistakes:

• Assuming binding is always correct without verification
• Thinking # wildcard doesn't match multiple words
• Ignoring exchange type setting

5. You want to receive all messages related to any fruit except those about apples or bananas using a topic exchange. Which binding key pattern should you use?

hard

A. *.fruit.*

B. #.fruit.# and bind separate queues for apple and banana to discard

C. #.fruit.# but exclude apple and banana keys manually

D. #.fruit.#

Solution

1. Step 1: Understand topic exchange limitations

   Topic exchanges route messages by matching patterns but cannot exclude specific keys directly in binding patterns.

2. Step 2: Plan a solution using multiple queues

   Bind one queue with #.fruit.# to get all fruit messages. Bind separate queues for apple and banana keys to handle or discard them separately.

3. Step 3: Implement exclusion by filtering in consumers or separate queues

   Since exclusion is not supported in binding keys, use separate queues or consumer logic to exclude apples and bananas.

4. Final Answer:

   #.fruit.# and bind separate queues for apple and banana to discard -> Option B

5. Quick Check:

   Exclusion requires separate queues or consumer filtering [OK]

Hint: Topic exchange can't exclude keys; use separate queues [OK]

Common Mistakes:

• Trying to exclude keys using binding patterns
• Assuming * or # can exclude specific words
• Not using multiple queues or consumer filtering