Work queue for task distribution in RabbitMQ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a durable queue named 'task_queue'.

RabbitMQ

channel.queue_declare(queue='task_queue', durable=[1])

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

ANone

BFalse

CTrue

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Setting durable to False causes the queue to be deleted on server restart.

Setting durable=True makes the queue survive RabbitMQ restarts, which is important for work queues.

2fill in blank

medium

Complete the code to send a persistent message to the 'task_queue'.

RabbitMQ

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

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

A1

B2

C0

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using delivery_mode=1 sends non-persistent messages.

Setting delivery_mode=2 marks the message as persistent, so it won't be lost if RabbitMQ restarts.

3fill in blank

hard

Fix the error in the consumer code to acknowledge messages manually.

RabbitMQ

channel.basic_consume(queue='task_queue', on_message_callback=callback, auto_ack=[1])

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

ANone

BTrue

C0

DFalse

Attempts:

3 left

💡 Hint

Common Mistakes

Setting auto_ack to True causes messages to be lost if the consumer crashes.

Setting auto_ack=False means the consumer will send an acknowledgment after processing each message, which is important for work queues.

4fill in blank

hard

Fill both blanks to set prefetch count to 1 and declare a durable queue.

RabbitMQ

channel.basic_qos(prefetch_count=[1])
channel.queue_declare(queue='task_queue', durable=[2])

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

A1

B0

CTrue

DFalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using prefetch_count=0 disables fair dispatch, and durable=False makes the queue temporary.

Setting prefetch_count=1 tells RabbitMQ not to give more than one message to a worker at a time. Declaring the queue as durable ensures it survives restarts.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps each word to its length only if length is greater than 3.

RabbitMQ

lengths = { [1] : [2] for [3] in words if len([3]) > 3 }

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

Aword

Blen(word)

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in different parts of the comprehension.

This comprehension creates a dictionary where keys are words and values are their lengths, but only for words longer than 3 characters.

Practice

1. What is the main purpose of a work queue in RabbitMQ?

easy

A. To create a backup of messages

B. To distribute tasks among multiple workers safely

C. To store user login information

D. To encrypt messages for security

Solution

1. Step 1: Understand the role of work queues

   Work queues are designed to share tasks among many workers so that the workload is balanced and tasks are processed efficiently.

2. Step 2: Eliminate unrelated options

   Storing login info, backing up messages, or encrypting messages are not the primary functions of work queues.

3. Final Answer:

   To distribute tasks among multiple workers safely -> Option B

4. Quick Check:

   Work queue = task distribution [OK]

Hint: Work queues share tasks among workers, not store or encrypt data [OK]

Common Mistakes:

• Confusing work queues with message encryption
• Thinking work queues store user data
• Assuming work queues backup messages automatically

2. Which RabbitMQ queue declaration option makes the queue survive server restarts?

easy

A. durable: true

B. autoDelete: true

C. exclusive: true

D. passive: true

Solution

1. Step 1: Identify durability option

   The 'durable: true' option ensures the queue is saved to disk and survives RabbitMQ server restarts.

2. Step 2: Understand other options

   'autoDelete' removes the queue when no consumers remain, 'exclusive' restricts queue to one connection, and 'passive' checks for queue existence without creating it.

3. Final Answer:

   durable: true -> Option A

4. Quick Check:

   durable = survive restart [OK]

Hint: Durable queues survive restarts; autoDelete removes queues [OK]

Common Mistakes:

• Using autoDelete instead of durable for persistence
• Confusing exclusive with durability
• Thinking passive creates durable queues

3. Given this worker code snippet in Python using pika:

channel.basic_consume(queue='task_queue', on_message_callback=callback, auto_ack=False)
channel.start_consuming()

What happens if the worker crashes before sending an acknowledgment?

medium

A. The message is requeued and delivered to another worker

B. The queue deletes all messages

C. The message is acknowledged automatically

D. The message is lost and never processed again

Solution

1. Step 1: Understand auto_ack=False behavior

   With auto_ack set to False, the worker must explicitly acknowledge messages after processing.

2. Step 2: Effect of worker crash before ack

   If the worker crashes before ack, RabbitMQ requeues the message to deliver it to another worker, ensuring no task is lost.

3. Final Answer:

   The message is requeued and delivered to another worker -> Option A

4. Quick Check:

   auto_ack=False + crash = requeue message [OK]

Hint: auto_ack=False means unacked messages get requeued on crash [OK]

Common Mistakes:

• Assuming messages are lost without ack
• Thinking messages auto-acknowledge on delivery
• Believing queue deletes messages on worker failure

4. You wrote this code to declare a durable queue:

channel.queue_declare(queue='task_queue', durable=False)

Why might this cause task loss after RabbitMQ restarts?

medium

A. Because exclusive=True is missing

B. Because the queue name is invalid

C. Because durable=True deletes messages on restart

D. Because durable=False means the queue is deleted on restart

Solution

1. Step 1: Analyze durable flag effect

   Setting durable=False means the queue is temporary and will be deleted when RabbitMQ restarts.

2. Step 2: Consequence on task persistence

   Since the queue is deleted, any unprocessed tasks in it are lost after restart.

3. Final Answer:

   Because durable=False means the queue is deleted on restart -> Option D

4. Quick Check:

   durable=False = queue lost on restart [OK]

Hint: durable=False queues vanish on restart, losing tasks [OK]

Common Mistakes:

• Confusing durable with exclusive
• Thinking queue name causes loss
• Believing durable=True deletes messages

5. You want to ensure tasks are not lost even if RabbitMQ crashes and workers fail. Which combination of settings should you use for the queue and messages?

hard

A. Declare queue with autoDelete=true and publish messages with delivery_mode=1

B. Declare queue with exclusive=true and publish messages with delivery_mode=1

C. Declare queue with durable=true and publish messages with delivery_mode=2

D. Declare queue with durable=false and publish messages with delivery_mode=2

Solution

1. Step 1: Ensure queue durability

   Setting durable=true makes the queue survive RabbitMQ restarts, preventing loss of the queue itself.

2. Step 2: Make messages persistent

   Publishing messages with delivery_mode=2 marks them as persistent, so they are saved to disk and not lost on server crash.

3. Step 3: Understand why other options fail

   autoDelete=true deletes the queue when no consumers remain, exclusive=true restricts queue to one connection, and durable=false means queue is temporary. delivery_mode=1 means messages are transient and can be lost.

4. Final Answer:

   Declare queue with durable=true and publish messages with delivery_mode=2 -> Option C

5. Quick Check:

   durable queue + persistent messages = no loss [OK]

Hint: Durable queue + delivery_mode=2 messages prevent loss [OK]

Common Mistakes:

• Using autoDelete instead of durable for persistence
• Publishing messages without delivery_mode=2
• Confusing exclusive with durability