Reply-to queue pattern in RabbitMQ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a temporary reply queue in RabbitMQ.

RabbitMQ

channel.queue_declare(queue=[1], exclusive=True)

Drag options to blanks, or click blank then click option'

A""

B"main_queue"

C"reply_queue"

D"task_queue"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a fixed queue name instead of an empty string.

Not setting the queue as exclusive.

Using an empty string "" tells RabbitMQ to create a unique, exclusive, and temporary queue for replies.

2fill in blank

medium

Complete the code to set the reply_to property in the message properties.

RabbitMQ

channel.basic_publish(exchange='', routing_key='task_queue', properties=pika.BasicProperties(reply_to=[1]), body='Hello')

Drag options to blanks, or click blank then click option'

A"main_queue"

B"callback_queue"

Ccallback_queue

Dreply_queue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a quoted string literal instead of the variable.

Using the wrong queue name.

The reply_to property should reference the callback_queue variable containing the reply queue name. No quotes are needed as it is already a string variable.

3fill in blank

hard

Fix the error in the callback function to correctly acknowledge the message.

RabbitMQ

def on_response(ch, method, props, body):
    if props.correlation_id == corr_id:
        response = body
    ch.basic_ack([1])

Drag options to blanks, or click blank then click option'

Amethod.delivery_tag

Bprops.delivery_tag

Cbody.delivery_tag

Dch.delivery_tag

Attempts:

3 left

💡 Hint

Common Mistakes

Using properties or channel instead of method for delivery tag.

Not acknowledging the message at all.

The basic_ack method requires the delivery tag from the method parameter to acknowledge the message.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps words to their lengths only if length is greater than 3.

RabbitMQ

{word: [1] for word in words if [2] > 3}

Drag options to blanks, or click blank then click option'

Alen(word)

Cword

Attempts:

3 left

💡 Hint

Common Mistakes

Using the word itself instead of its length.

Checking the word instead of its length in the condition.

The dictionary comprehension maps each word to its length using len(word) and filters words with length greater than 3.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps uppercase keys to values only if value is positive.

RabbitMQ

result = { [1]: [2] for k, v in data.items() if v [3] 0 }

Drag options to blanks, or click blank then click option'

Ak.upper()

Bv

C>

Dk.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase keys instead of uppercase.

Using wrong comparison operators.

Swapping keys and values.

The comprehension uses k.upper() as keys, v as values, and filters values greater than zero.

Practice

1. What is the main purpose of the amq.rabbitmq.reply-to queue in RabbitMQ's reply-to queue pattern?

easy

A. To provide a temporary queue for direct replies without manual queue creation

B. To permanently store all messages sent to RabbitMQ

C. To route messages to multiple consumers simultaneously

D. To act as a dead-letter queue for failed messages

Solution

1. Step 1: Understand the reply-to queue pattern

   The pattern uses a special queue to receive replies directly without creating separate queues manually.

2. Step 2: Identify the role of amq.rabbitmq.reply-to

   This queue is a built-in temporary queue that simplifies reply handling by avoiding manual queue management.

3. Final Answer:

   To provide a temporary queue for direct replies without manual queue creation -> Option A

4. Quick Check:

   Reply-to queue = temporary direct reply queue [OK]

Hint: Remember reply-to queue is temporary and automatic [OK]

Common Mistakes:

• Thinking it stores all messages permanently
• Confusing it with dead-letter queues
• Assuming it routes messages to many consumers

2. Which of the following is the correct way to set the reply-to property in a RabbitMQ message to use the reply-to queue pattern?

easy

A. Set reply-to to the consumer tag

B. Set reply-to to an empty string

C. Set reply-to to 'amq.rabbitmq.reply-to'

D. Set reply-to to the exchange name

Solution

1. Step 1: Recall the special reply-to queue name

   The reply-to queue pattern uses the exact name 'amq.rabbitmq.reply-to' to indicate direct reply handling.

2. Step 2: Match the correct reply-to property value

   Setting reply-to to 'amq.rabbitmq.reply-to' enables the client to receive replies on the special temporary queue.

3. Final Answer:

   Set reply-to to 'amq.rabbitmq.reply-to' -> Option C

4. Quick Check:

   Reply-to property = 'amq.rabbitmq.reply-to' [OK]

Hint: Use exact string 'amq.rabbitmq.reply-to' for reply-to [OK]

Common Mistakes:

• Leaving reply-to empty disables replies
• Using consumer tag instead of queue name
• Confusing exchange name with reply-to queue

3. Given this simplified Python code snippet using pika library, what will be printed?

import pika

connection = pika.BlockingConnection(pika.ConnectionParameters('localhost'))
channel = connection.channel()

channel.basic_publish(
    exchange='',
    routing_key='rpc_queue',
    properties=pika.BasicProperties(reply_to='amq.rabbitmq.reply-to'),
    body='Hello')

print('Message sent with reply-to')
connection.close()

medium

A. Message sent without reply-to

B. Message sent with reply-to

C. No output because connection is closed

D. Error: reply_to property invalid

Solution

1. Step 1: Analyze the code message publishing

   The code publishes a message with reply_to set to 'amq.rabbitmq.reply-to', which is valid syntax.

2. Step 2: Check the print statement execution

   After publishing, the print statement outputs the confirmation message before closing the connection.

3. Final Answer:

   Message sent with reply-to -> Option B

4. Quick Check:

   Print confirms message sent with reply-to [OK]

Hint: Print confirms message sent, no error if syntax correct [OK]

Common Mistakes:

• Assuming reply_to causes error
• Thinking connection close stops print
• Confusing reply_to with routing_key

4. You wrote a RabbitMQ client that sets the reply-to property to 'amq.rabbitmq.reply-to' but never receives replies. What is the most likely cause?

medium

A. The exchange name is missing in the publish call

B. The reply-to queue name is misspelled

C. The routing key is incorrect

D. The client did not start consuming from the reply-to queue

Solution

1. Step 1: Understand reply-to queue usage

   Using 'amq.rabbitmq.reply-to' requires the client to consume from this special queue to get replies.

2. Step 2: Identify missing consumption

   If the client does not start consuming from the reply-to queue, replies will not be received despite correct reply-to setting.

3. Final Answer:

   The client did not start consuming from the reply-to queue -> Option D

4. Quick Check:

   Must consume reply-to queue to get replies [OK]

Hint: Always consume from reply-to queue to receive replies [OK]

Common Mistakes:

• Ignoring consumption step
• Assuming reply-to queue auto-delivers replies
• Confusing routing key with reply-to queue

5. You want to implement an RPC client using RabbitMQ's reply-to queue pattern. Which sequence correctly describes the steps to send a request and receive a reply?

hard

A. Publish message with reply-to='amq.rabbitmq.reply-to', start consuming from reply-to queue, wait for reply

B. Create a new queue manually, publish message with reply-to set to new queue, consume from new queue

C. Publish message without reply-to, consume from default queue, wait for reply

D. Publish message with reply-to set to exchange name, consume from exchange

Solution

1. Step 1: Use the special reply-to queue in publishing

   Set reply-to property to 'amq.rabbitmq.reply-to' to use the built-in temporary reply queue.

2. Step 2: Start consuming from the reply-to queue

   Begin consuming from 'amq.rabbitmq.reply-to' to receive the server's reply message.

3. Step 3: Wait and process the reply

   Wait for the reply message on the reply-to queue and process it as the RPC response.

4. Final Answer:

   Publish message with reply-to='amq.rabbitmq.reply-to', start consuming from reply-to queue, wait for reply -> Option A

5. Quick Check:

   Publish with reply-to + consume reply-to = RPC client [OK]

Hint: Publish with reply-to and consume reply-to for RPC [OK]

Common Mistakes:

• Manually creating reply queues unnecessarily
• Setting reply-to to exchange instead of queue
• Not consuming from reply-to queue