Request-reply pattern in RabbitMQ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a queue named 'rpc_queue' in RabbitMQ.

RabbitMQ

channel.queue_declare(queue='[1]')

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

Ahello

Blogs

Ctask_queue

Drpc_queue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different queue name like 'task_queue' or 'hello' which is not for RPC.

The queue name for the request-reply pattern is typically 'rpc_queue'. This code declares that queue.

2fill in blank

medium

Complete the code to send a message with a unique correlation_id for the RPC request.

RabbitMQ

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

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

Acorr_id_abc

Bunique_id_1

C12345

Drequest_1

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-unique or numeric IDs that don't help match replies.

The correlation_id is a unique string to match requests and replies. 'corr_id_abc' is a typical example.

3fill in blank

hard

Fix the error in the code to consume messages from the callback queue with auto_ack enabled.

RabbitMQ

channel.basic_consume(queue='[1]', on_message_callback=on_response, auto_ack=True)

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

Areply_queue

Bcallback_queue

Cresponse_queue

Drpc_queue

Attempts:

3 left

💡 Hint

Common Mistakes

Using the request queue name instead of the callback queue.

The client listens on a callback queue, often named 'callback_queue', to receive replies.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that filters messages with correlation_id matching 'corr_id_abc'.

RabbitMQ

filtered = {k: v for k, v in messages.items() if k [1] '[2]'}

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

A==

Bcorr_id_abc

C!=

Drequest_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' or wrong string for correlation id.

The comprehension keeps items where the key equals 'corr_id_abc', matching the request.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps message IDs to bodies for messages with body length greater than 5.

RabbitMQ

result = { [1]: [2] for [3], [2] in messages.items() if len([2]) > 5 }

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

Amsg_id

Bbody

Dmsg

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing variable names or using inconsistent keys and values.

The comprehension uses 'msg_id' as key and 'body' as value, iterating over messages.

Practice

1.

What is the main purpose of the reply_to property in RabbitMQ's request-reply pattern?

easy

A. It identifies the sender of the request message.

B. It tells the receiver where to send the reply message.

C. It encrypts the message content for security.

D. It sets the priority of the message in the queue.

Solution

1. Step 1: Understand the role of reply_to

   The reply_to property specifies the queue where the reply should be sent.

2. Step 2: Differentiate from other properties

   Unlike sender identification or encryption, reply_to directs the response path.

3. Final Answer:

   It tells the receiver where to send the reply message. -> Option B

4. Quick Check:

   reply_to = reply destination [OK]

Hint: Remember: reply_to points to the reply queue [OK]

Common Mistakes:

• Confusing reply_to with sender ID
• Thinking reply_to sets message priority
• Assuming reply_to encrypts messages

2.

Which of the following is the correct way to set the correlation_id in a RabbitMQ message using Python pika library?

channel.basic_publish(exchange='', routing_key='rpc_queue', properties=..., body='Hello')

easy

A. properties=pika.BasicProperties(correlationId='12345')

B. properties=pika.BasicProperties(correlation='12345')

C. properties=pika.BasicProperties(corr_id='12345')

D. properties=pika.BasicProperties(correlation_id='12345')

Solution

1. Step 1: Recall correct property name

   The correct property name for correlation is correlation_id in pika.BasicProperties.

2. Step 2: Match syntax exactly

   properties=pika.BasicProperties(correlation_id='12345') uses the exact correct syntax: correlation_id='12345'.

3. Final Answer:

   properties=pika.BasicProperties(correlation_id='12345') -> Option D

4. Quick Check:

   Correct property name = correlation_id [OK]

Hint: Use exact property names from docs: correlation_id [OK]

Common Mistakes:

• Using incorrect property names like correlation or corr_id
• Capitalizing property names incorrectly
• Omitting properties argument

3.

Given this Python code snippet using pika for request-reply, what will be printed?

import pika

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

channel.queue_declare(queue='rpc_queue')

corr_id = 'abc123'

channel.basic_publish(
    exchange='',
    routing_key='rpc_queue',
    properties=pika.BasicProperties(reply_to='reply_queue', correlation_id=corr_id),
    body='Request')

print(corr_id)

medium

A. abc123

B. Request

C. reply_queue

D. Error: missing callback

Solution

1. Step 1: Identify what is printed

   The code prints the variable corr_id which is set to 'abc123'.

2. Step 2: Understand message sending vs printing

   Sending a message does not affect the print statement; it prints the variable value.

3. Final Answer:

   abc123 -> Option A

4. Quick Check:

   Printed variable = corr_id = abc123 [OK]

Hint: Print shows variable, not message content or errors [OK]

Common Mistakes:

• Confusing printed output with message body
• Expecting error due to missing reply handler
• Thinking reply_to value is printed

4.

In a request-reply setup, a developer notices replies never arrive. Which fix addresses this common error?

channel.basic_publish(exchange='', routing_key='rpc_queue', properties=pika.BasicProperties(), body='Hello')

medium

A. Remove exchange parameter completely.

B. Change routing_key to reply_queue.

C. Add reply_to and correlation_id in properties.

D. Set body to empty string.

Solution

1. Step 1: Identify missing properties

   The message lacks reply_to and correlation_id, needed for replies.

2. Step 2: Add these properties to enable reply routing

   Including reply_to tells where to send replies; correlation_id matches responses.

3. Final Answer:

   Add reply_to and correlation_id in properties. -> Option C

4. Quick Check:

   Missing reply_to/correlation_id blocks replies [OK]

Hint: Always set reply_to and correlation_id for replies [OK]

Common Mistakes:

• Changing routing_key instead of adding properties
• Removing exchange causes unrelated errors
• Setting empty body does not fix reply issues

5.

You want to implement a request-reply pattern where multiple clients send requests and receive replies without mixing responses. Which approach ensures correct matching?

hard

A. Use a unique correlation_id per request and a shared reply queue.

B. Use the same correlation_id for all requests and separate reply queues.

C. Use unique correlation_id per client and unique reply queues per client.

D. Use no correlation_id and a shared reply queue.

Solution

1. Step 1: Understand correlation_id role

   A unique correlation_id lets clients match replies to requests even on a shared reply queue.

2. Step 2: Evaluate reply queue usage

   Using a shared reply queue with unique IDs is efficient and common practice.

3. Final Answer:

   Use a unique correlation_id per request and a shared reply queue. -> Option A

4. Quick Check:

   Unique correlation_id + shared queue = correct matching [OK]

Hint: Unique correlation_id with shared reply queue avoids mix-ups [OK]

Common Mistakes:

• Using same correlation_id causes reply confusion
• Creating many reply queues adds complexity
• Omitting correlation_id breaks matching