The answer is that the Lambda function execution time exceeds API Gateway's 29-second timeout, causing the 502 Bad Gateway error. This occurs because API Gateway enforces a hard 29-second limit for integration responses; if your Lambda function runs longer, API Gateway terminates the connection and returns a 502, even though the function itself completes successfully—which is why the Lambda logs show no errors. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of API Gateway’s service limits versus Lambda’s own timeout (which defaults to 3 seconds but can be set up to 15 minutes). A common trap is assuming the error originates in Lambda, but the key clue is the absence of errors in the function logs. Memory tip: think of the 29-second timeout as the "gateway's gate"—once it closes, the response never gets through.
DVA-C02 Troubleshooting and Optimization Practice Question
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. 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 runs a serverless application using AWS Lambda and Amazon API Gateway. The application experiences intermittent 502 Bad Gateway errors. The Lambda function logs show no errors. 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 execution time exceeds API Gateway's 29-second timeout.
The most likely cause is that the Lambda function execution time exceeds API Gateway's 29-second timeout. API Gateway has a hard limit of 29 seconds for integration responses, and if the Lambda function takes longer, API Gateway returns a 502 Bad Gateway error. Since the Lambda logs show no errors, the function is running successfully but timing out at the API Gateway level, not failing within Lambda itself.
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 execution time exceeds API Gateway's 29-second timeout.
Why this is correct
API Gateway has a 29-second integration timeout; exceeding it causes 502 errors.
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 API Gateway account-level throttling limit is exceeded.
Why it's wrong here
Throttling returns 429 errors.
✗
The Lambda function is throwing unhandled exceptions.
Why it's wrong here
Unhandled exceptions appear in Lambda logs.
✗
The API Gateway request payload exceeds 10 MB.
Why it's wrong here
Payload too large results in 413 errors.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume 502 errors always indicate Lambda function failures, but API Gateway's 29-second timeout is a separate, often overlooked limit that causes 502 errors even when the Lambda function runs successfully.
Detailed technical explanation
How to think about this question
API Gateway's integration timeout is 29 seconds for all integration types, including Lambda proxy integrations. When the timeout is reached, API Gateway terminates the connection and returns a 502 response without waiting for the Lambda function to complete. This is distinct from Lambda's own function timeout (which defaults to 3 seconds and can be set up to 15 minutes), so a function can complete successfully within its own timeout but still trigger a 502 if it exceeds API Gateway's 29-second limit. In real-world scenarios, this often occurs with cold starts or functions processing large datasets where execution time varies.
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.
Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The Lambda function execution time exceeds API Gateway's 29-second timeout. — The most likely cause is that the Lambda function execution time exceeds API Gateway's 29-second timeout. API Gateway has a hard limit of 29 seconds for integration responses, and if the Lambda function takes longer, API Gateway returns a 502 Bad Gateway error. Since the Lambda logs show no errors, the function is running successfully but timing out at the API Gateway level, not failing within Lambda itself.
What should I do if I get this DVA-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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