The answer is that the event source mapping has MaximumRetryAttempts set to 0. This is correct because even when an SQS queue is configured with a redrive policy to move messages to a DLQ after 3 receive attempts, the Lambda event source mapping has its own independent retry policy that controls how many times Lambda will retry a failed invocation before allowing the message to become visible again in the queue. When MaximumRetryAttempts is set to 0, Lambda immediately discards the failed invocation without retrying, so the message never gets reprocessed and the SQS receive count never increments past 1, preventing the redrive policy from ever triggering. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this question tests your understanding of the interaction between Lambda’s asynchronous invocation retry behavior and SQS’s redrive policy—a common trap is assuming the SQS redrive policy alone controls retries, when in fact the event source mapping’s MaximumRetryAttempts overrides it. Remember the mnemonic: “Zero retries, zero progress—check the mapping, not the queue.”
DOP-C02 Incident and Event Response Practice Question
This DOP-C02 practice question tests your understanding of incident and event response. 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 company uses AWS Lambda functions to process messages from an Amazon SQS queue. The Lambda function sometimes fails due to a transient error in a downstream API. The DevOps engineer wants to ensure that failed messages are retried automatically and eventually sent to a dead-letter queue after 3 failed attempts. The SQS queue is configured with a redrive policy that moves messages to a DLQ after 3 receive attempts. However, Lambda functions that fail are not being retried. What is the MOST likely reason?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The event source mapping has 'MaximumRetryAttempts' set to 0.
Option D is correct because by default, if a Lambda function fails, the SQS queue treats the message as received and increments the receive count. If the function does not delete the message and returns an error, the message becomes visible again after the visibility timeout. However, if the function returns an error, Lambda will automatically retry the invocation up to 2 times (for a total of 3 attempts) based on the function's retry policy. But if the function is configured with 'MaximumRetryAttempts' set to 0 in its event source mapping, then no retries will occur. The question states that the SQS redrive policy should handle retries after 3 receive attempts, but if the Lambda function is not retrying, it's likely because the event source mapping's 'MaximumRetryAttempts' is set to 0. Option A is wrong because DLQ is configured on the SQS queue, not Lambda. Option B is wrong because the visibility timeout affects when the message becomes visible again, but if the function fails, the message will be retried based on the event source mapping settings. Option C is wrong because the batch size does not affect retries.
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.
✗
The batch size is set to 1, preventing retries.
Why it's wrong here
Batch size does not affect retry behavior.
✗
The visibility timeout is set too low, causing messages to be retried immediately.
Why it's wrong here
A low visibility timeout would cause more retries, not prevent them.
✓
The event source mapping has 'MaximumRetryAttempts' set to 0.
Why this is correct
Setting MaximumRetryAttempts to 0 disables retries by Lambda, so the function is invoked only once per message.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The dead-letter queue is not configured on the Lambda function.
Why it's wrong here
DLQ is configured on the SQS queue, not Lambda.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 DOP-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Incident and Event Response — This question tests Incident and Event Response — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The event source mapping has 'MaximumRetryAttempts' set to 0. — Option D is correct because by default, if a Lambda function fails, the SQS queue treats the message as received and increments the receive count. If the function does not delete the message and returns an error, the message becomes visible again after the visibility timeout. However, if the function returns an error, Lambda will automatically retry the invocation up to 2 times (for a total of 3 attempts) based on the function's retry policy. But if the function is configured with 'MaximumRetryAttempts' set to 0 in its event source mapping, then no retries will occur. The question states that the SQS redrive policy should handle retries after 3 receive attempts, but if the Lambda function is not retrying, it's likely because the event source mapping's 'MaximumRetryAttempts' is set to 0. Option A is wrong because DLQ is configured on the SQS queue, not Lambda. Option B is wrong because the visibility timeout affects when the message becomes visible again, but if the function fails, the message will be retried based on the event source mapping settings. Option C is wrong because the batch size does not affect retries.
What should I do if I get this DOP-C02 question wrong?
Identify which DOP-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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