Queue length limits in RabbitMQ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a maximum length of 1000 messages for the queue.

RabbitMQ

rabbitmqctl set_policy TTL "^queue_name$" '{"max-length": [1]' --apply-to queues

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

A1000

B5000

C100

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 disables the limit, which is not the goal.

Setting too high a number may cause memory issues.

The max-length property limits the queue to 1000 messages.

2fill in blank

medium

Complete the code to declare a queue with a maximum length of 500 messages using the RabbitMQ management plugin.

RabbitMQ

rabbitmqadmin declare queue name=my_queue durable=true arguments='{"[1]":500}'

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

Ax-max-length

Bmax-length

Cmax_messages

Dqueue-length

Attempts:

3 left

💡 Hint

Common Mistakes

Using max-length without the x- prefix causes the setting to be ignored.

The argument x-max-length sets the maximum number of messages the queue can hold.

3fill in blank

hard

Fix the error in the policy JSON to correctly limit the queue length to 2000 messages.

RabbitMQ

rabbitmqctl set_policy limit_length ".*" '{"[1]": 2000}' --apply-to queues

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

Aqueue-max-length

Bx-max-length

Cmax_length

Dmax-length

Attempts:

3 left

💡 Hint

Common Mistakes

Using x-max-length causes the policy to be ignored.

The correct key for queue length limit in policies is max-length.

4fill in blank

hard

Fill both blanks to declare a queue with a max length of 300 and a max priority of 10.

RabbitMQ

rabbitmqadmin declare queue name=priority_queue durable=true arguments='{"[1]":300, "[2]":10}'

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

Ax-max-length

Bx-max-priority

Cmax-length

Dmax-priority

Attempts:

3 left

💡 Hint

Common Mistakes

Using keys without x- prefix will not apply the settings.

x-max-length sets the queue length limit, and x-max-priority sets the max priority.

5fill in blank

hard

Fill all three blanks to create a policy named 'limit_policy' that applies to all queues, setting max length to 1500 and overflow behavior to drop oldest messages.

RabbitMQ

rabbitmqctl set_policy [1] ".*" '{"[2]":1500, "[3]":"drop-head"}' --apply-to queues

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

Alimit_policy

Bx-max-length

Coverflow

Dmax-length

Attempts:

3 left

💡 Hint

Common Mistakes

Using x-max-length instead of max-length.

Using x-overflow instead of overflow.

The policy name is limit_policy. The key max-length sets the max messages, and overflow controls overflow behavior.

Practice

1. What is the main purpose of setting a max-length limit on a RabbitMQ queue?

easy

A. To encrypt messages in the queue

B. To increase the speed of message delivery

C. To limit the number of messages the queue can hold to prevent overload

D. To allow unlimited messages in the queue

Solution

1. Step 1: Understand queue length limits

   Queue length limits control how many messages a queue can hold to avoid memory overload.

2. Step 2: Identify the purpose of max-length

   The max-length setting limits the number of messages to prevent backlog and resource exhaustion.

3. Final Answer:

   To limit the number of messages the queue can hold to prevent overload -> Option C

4. Quick Check:

   Queue length limits = prevent overload [OK]

Hint: Queue length limits prevent too many messages piling up [OK]

Common Mistakes:

• Thinking max-length speeds up delivery
• Confusing max-length with encryption
• Assuming queues can hold unlimited messages

2. Which of the following is the correct syntax to set a queue length limit of 1000 messages using rabbitmqctl?

easy

A. rabbitmqctl set_policy mypolicy "^myqueue$" '{"max-length":1000}' --apply-to queues

B. rabbitmqctl set_policy mypolicy "myqueue" '{max-length=1000}' --apply-to queues

C. rabbitmqctl set_policy mypolicy "^myqueue$" '{max-length:1000}' --apply-to queues

D. rabbitmqctl set_policy mypolicy "^myqueue$" '{"max-length"=1000}' --apply-to queues

Solution

1. Step 1: Review correct JSON syntax for policy

   The policy value must be a JSON string with double quotes around keys and values, e.g., '{"max-length":1000}'.

2. Step 2: Check the full command syntax

   The correct command uses regex pattern with ^ and $ for exact queue name, and --apply-to queues to target queues.

3. Final Answer:

   rabbitmqctl set_policy mypolicy "^myqueue$" '{"max-length":1000}' --apply-to queues -> Option A

4. Quick Check:

   Correct JSON and command syntax = rabbitmqctl set_policy mypolicy "^myqueue$" '{"max-length":1000}' --apply-to queues [OK]

Hint: Use double quotes and JSON format for policy values [OK]

Common Mistakes:

• Using single quotes inside JSON incorrectly
• Missing regex anchors ^ and $
• Using = instead of : in JSON

3. Given the policy set with rabbitmqctl set_policy limit1000 "^task_queue$" '{"max-length":1000}' --apply-to queues, what happens when the queue task_queue receives its 1001st message?

medium

A. The new message is rejected and not added to the queue

B. The oldest message in the queue is dropped to make room for the new one

C. The queue size automatically increases to hold the new message

D. RabbitMQ crashes due to overflow

Solution

1. Step 1: Understand max-length behavior

   When max-length is reached, RabbitMQ drops oldest messages to keep queue size within limit.

2. Step 2: Apply to the 1001st message

   On the 1001st message, the oldest message is removed to add the new one, maintaining max 1000 messages.

3. Final Answer:

   The oldest message in the queue is dropped to make room for the new one -> Option B

4. Quick Check:

   max-length reached = oldest message dropped [OK]

Hint: max-length drops oldest message, never rejects new [OK]

Common Mistakes:

• Thinking new messages get rejected
• Assuming queue size auto-expands
• Believing RabbitMQ crashes on overflow

4. You tried to set a queue length limit with this command: rabbitmqctl set_policy limit "^queue$" '{max-length:500}' --apply-to queues but it did not work. What is the error?

medium

A. The JSON policy value keys and values must be double quoted strings

B. The JSON policy value uses colon instead of equal sign

C. The JSON policy value uses single quotes instead of double quotes

D. The regex pattern is missing anchors ^ and $

Solution

1. Step 1: Check JSON syntax in policy

   JSON requires keys and string values to be double quoted, e.g., '{"max-length":500}'.

2. Step 2: Identify the error in given command

   The command uses '{max-length:500}' without quotes around key, which is invalid JSON.

3. Final Answer:

   The JSON policy value keys and values must be double quoted strings -> Option A

4. Quick Check:

   JSON keys/values need double quotes [OK]

Hint: Always double quote keys and string values in JSON [OK]

Common Mistakes:

• Using single quotes inside JSON
• Using colon instead of colon (correct is colon)
• Ignoring regex anchors (not error here)

5. You want to limit a queue named logs to 500 messages but also want to drop messages older than 1 hour. Which policy configuration correctly applies both limits?

hard

A. rabbitmqctl set_policy loglimit "^logs$" '{"max-length":500, "max-age":60}' --apply-to queues

B. rabbitmqctl set_policy loglimit "^logs$" '{"max-length":500, "max-age":3600}' --apply-to queues

C. rabbitmqctl set_policy loglimit "^logs$" '{"max-length":500, "max-age":60000}' --apply-to queues

D. rabbitmqctl set_policy loglimit "^logs$" '{"max-length":500, "max-age":3600000}' --apply-to queues

Solution

1. Step 1: Understand max-age unit

   RabbitMQ's max-age is in milliseconds, so 1 hour = 3600000 ms.

2. Step 2: Check policy JSON for both limits

   The policy must include both "max-length":500 and "max-age":3600000 correctly formatted.

3. Final Answer:

   rabbitmqctl set_policy loglimit "^logs$" '{"max-length":500, "max-age":3600000}' --apply-to queues -> Option D

4. Quick Check:

   1 hour = 3600000 ms, both limits set [OK]

Hint: Remember max-age is milliseconds, 1 hour = 3600000 [OK]

Common Mistakes:

• Using seconds or minutes instead of milliseconds
• Missing one of the limits in policy
• Incorrect JSON formatting