The correct approach is to create a CloudWatch alarm on the ApproximateNumberOfMessagesVisible metric of the dead-letter queue. This metric directly counts the messages that have failed processing and been moved to the DLQ, so an alarm triggering when this value exceeds zero provides a precise, real-time alert for processing failures without needing to parse Lambda logs or rely on indirect indicators like function error rates. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of how SQS metrics map to operational signals—a common trap is choosing a Lambda error metric, which can miss failures caused by downstream timeouts or partial batch processing. Remember the memory tip: "DLQ visible = failure audible," meaning the visible message count in the dead-letter queue is the clearest audible alert for processing failures.
DOP-C02 Monitoring and Logging Practice Question
This DOP-C02 practice question tests your understanding of monitoring and logging. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A DevOps engineer needs to set up a monitoring solution for an AWS Lambda function that processes messages from an Amazon SQS queue. The engineer wants to be alerted if the function fails to process a message (i.e., the message ends up in the dead-letter queue). Which approach should they use?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a CloudWatch alarm on the ApproximateNumberOfMessagesVisible metric of the dead-letter queue.
Option A is correct because the `ApproximateNumberOfMessagesVisible` metric on the dead-letter queue (DLQ) directly reflects the number of messages that have failed processing and been moved there. By creating a CloudWatch alarm on this metric (e.g., when it exceeds 0 for a period), the engineer receives an alert precisely when messages are failing, without needing to parse logs or rely on indirect indicators.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Create a CloudWatch alarm on the ApproximateNumberOfMessagesVisible metric of the dead-letter queue.
Why this is correct
This metric increases when messages are sent to the DLQ, triggering the alarm.
Related concept
Read the scenario before looking for a memorised answer.
✗
Enable CloudTrail to log SQS API calls and create a metric filter for SendMessage to the DLQ.
Why it's wrong here
CloudTrail does not capture SQS message-level operations like SendMessage to DLQ.
✗
Create a CloudWatch Events rule to monitor the Lambda function errors.
Configure the Lambda function's dead-letter queue to send notifications via Amazon SNS.
Why it's wrong here
Lambda's DLQ is for asynchronous invocation failures; SQS DLQ is different.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse monitoring Lambda function errors (Option C) with monitoring DLQ messages, not realizing that a message can end up in the DLQ due to exhaustion of retries (configured in the SQS event source mapping) without the Lambda function itself throwing an error.
Detailed technical explanation
How to think about this question
Under the hood, SQS publishes the `ApproximateNumberOfMessagesVisible` metric to CloudWatch every minute (for standard queues) or every 5 minutes (for FIFO queues), making it suitable for near-real-time alarming. A common subtlety is that the metric is approximate and may lag by up to 1-2 minutes, so alarms should use a period of at least 60 seconds and a threshold of >0 with a datapoint count of 1 to avoid false positives from transient spikes. In a real-world scenario, if the Lambda function has a reserved concurrency of 0 or throttles, messages may be sent to the DLQ without a corresponding Lambda error, making the DLQ metric the most reliable indicator.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Monitoring and Logging — This question tests Monitoring and Logging — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create a CloudWatch alarm on the ApproximateNumberOfMessagesVisible metric of the dead-letter queue. — Option A is correct because the `ApproximateNumberOfMessagesVisible` metric on the dead-letter queue (DLQ) directly reflects the number of messages that have failed processing and been moved there. By creating a CloudWatch alarm on this metric (e.g., when it exceeds 0 for a period), the engineer receives an alert precisely when messages are failing, without needing to parse logs or rely on indirect indicators.
What should I do if I get this DOP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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