Alerting on queue depth and consumer lag in RabbitMQ - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding queue depth alerting

What does monitoring the queue depth in RabbitMQ help you detect?

A It tracks the total number of messages published since server start.

B It shows the number of consumers connected to the queue.

C It measures the network latency between RabbitMQ nodes.

D It helps detect if messages are piling up, indicating slow processing or blocked consumers.

💡 Hint

Think about what it means if many messages wait in the queue.

Queue depth is the count of messages waiting to be processed. A high queue depth means messages are not being consumed fast enough, which can indicate slow consumers or issues in processing.

💻 Command Output

intermediate

Interpreting consumer lag from RabbitMQ CLI

Given the output below from rabbitmqctl list_queues name messages_ready messages_unacknowledged, what is the consumer lag?

queue1 10 5
queue2 0 0
queue3 3 7

RabbitMQ

rabbitmqctl list_queues name messages_ready messages_unacknowledged

A queue1 has 5 messages lagging; queue2 has 0; queue3 has 7 messages lagging.

B queue1 has a lag of 15 messages; queue2 has no lag; queue3 has a lag of 10 messages.

C queue1 has 10 messages lagging; queue2 has 0; queue3 has 3 messages lagging.

D queue1 has 10 messages ready only; consumer lag cannot be determined.

💡 Hint

Consumer lag is the sum of messages ready and unacknowledged.

Consumer lag is the total messages waiting to be processed (ready) plus those delivered but not yet acknowledged (unacknowledged). For queue1: 10 + 5 = 15.

❓ Configuration

advanced

Configuring alert for queue depth using Prometheus

Which Prometheus alert rule correctly triggers when RabbitMQ queue depth exceeds 1000 messages for more than 5 minutes?

A

alert: HighQueueDepth
expr: rabbitmq_queue_messages_ready > 1000
for: 5m
labels:
  severity: warning
annotations:
  summary: "Queue depth high"

B

alert: HighQueueDepth
expr: rabbitmq_queue_messages_ready >= 1000
for: 1m
labels:
  severity: critical
annotations:
  summary: "Queue depth high"

C

alert: HighQueueDepth
expr: rabbitmq_queue_messages_ready > 1000
labels:
  severity: warning
annotations:
  summary: "Queue depth high"

D

alert: HighQueueDepth
expr: rabbitmq_queue_messages_ready > 1000
for: 10m
labels:
  severity: warning
annotations:
  summary: "Queue depth high"

💡 Hint

Check the expression, threshold, and duration carefully.

The alert triggers if the queue depth metric is above 1000 for at least 5 minutes. Option A matches this exactly.

❓ Troubleshoot

advanced

Diagnosing consumer lag despite low queue depth

You notice consumer lag is high but the queue depth is low. What could cause this?

A Consumers have received messages but are slow to acknowledge them, causing unacknowledged messages to pile up.

B The RabbitMQ server is down, so no messages are processed.

C The queue is set to auto-delete, so messages are lost immediately.

D There are no consumers connected to the queue.

💡 Hint

Think about what unacknowledged messages mean.

High consumer lag with low ready messages means messages are delivered but not acknowledged, indicating slow or stuck consumers.

🔀 Workflow

expert

Designing an alert workflow for consumer lag and queue depth

Which sequence of steps correctly describes a workflow to alert on both queue depth and consumer lag in RabbitMQ?

A 2,1,3,4

B 3,1,2,4

C 1,2,3,4

D 1,3,2,4

💡 Hint

Think about the logical order from data collection to resolution.

First collect metrics, then set alerts, notify team, and finally investigate.