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 incoming events from Amazon S3. The operations team notices that some events are not being processed, and there is no error in the Lambda function logs. What is the most likely cause?
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 Lambda function has reserved concurrency set to a low value, causing throttling.
When a Lambda function has reserved concurrency set to a low value, it limits the number of concurrent executions allowed for that function. If incoming S3 events exceed this limit, the Lambda service throttles the invocations, causing some events to be silently dropped without generating errors in the function logs because the function never actually runs. This matches the symptom of missing events with no error logs.
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 Lambda function has reserved concurrency set to a low value, causing throttling.
Why this is correct
Throttled events are not logged in the function's CloudWatch Logs because the function is not invoked.
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 S3 event notification is configured to send to an SNS topic that is not subscribed to the Lambda function.
Why it's wrong here
This would result in an undeliverable notification error.
✗
The S3 bucket policy does not allow the Lambda function to be invoked.
Why it's wrong here
This would cause an error when S3 tries to invoke the function, logged in CloudTrail.
✗
The Lambda function has a timeout that is too short.
Why it's wrong here
A timeout would result in an error logged in CloudWatch.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume missing events are due to permission or timeout errors, but the absence of any error logs points to throttling, where the function is never invoked and thus no logs are generated.
Detailed technical explanation
How to think about this question
Lambda reserved concurrency acts as a hard limit on concurrent executions per function, separate from the account-level concurrency limit. When throttled, Lambda returns a 429 TooManyRequestsException to the event source (S3), which S3 treats as a transient failure and may retry based on its notification retry policy (typically up to 10 retries over 24 hours), but if the concurrency limit is persistently low, events can be dropped after retries are exhausted. This is a common issue in high-throughput S3 event processing where burst traffic exceeds reserved concurrency.
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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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.
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 Lambda function has reserved concurrency set to a low value, causing throttling. — When a Lambda function has reserved concurrency set to a low value, it limits the number of concurrent executions allowed for that function. If incoming S3 events exceed this limit, the Lambda service throttles the invocations, causing some events to be silently dropped without generating errors in the function logs because the function never actually runs. This matches the symptom of missing events with no error logs.
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.
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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Question Discussion
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