The answer is the Lambda function's execution role lacks an IAM policy allowing s3:PutObject. This is because AWS Lambda requires two distinct permission layers: a resource-based policy controls who can invoke the function, while the execution role governs what the function can do once running. When a Lambda function writes to S3, it acts under its execution role, not the resource-based policy—so even if S3 can trigger the function, the function itself cannot write without explicit s3:PutObject permission in that role. On the AWS Certified Developer Associate DVA-C02 exam, this distinction is a frequent trap: candidates often confuse resource-based policies (for invocation) with execution role policies (for actions). A common memory tip is "Invoke vs. Act: resource-based lets others call you, execution role lets you do things."
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 developer is troubleshooting an AWS Lambda function that writes to an S3 bucket. The function is configured with a resource-based policy that allows the S3 service to invoke the function. However, the function fails with an access denied error when trying to write to S3. 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's execution role does not have an IAM policy that allows s3:PutObject.
Option D is correct because the Lambda function needs an execution role with permissions to write to S3. The resource-based policy only allows S3 to invoke the function, not the function to write. Option A is wrong because bucket policy is not needed if the execution role has permissions. Option B is wrong because the function can be triggered correctly. Option C is wrong because VPC does not cause access denied.
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 is configured in a VPC without an S3 VPC endpoint.
Why it's wrong here
Would cause timeout, not access denied.
✓
The Lambda function's execution role does not have an IAM policy that allows s3:PutObject.
Why this is correct
Execution role must have S3 write permissions.
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 Lambda function's trigger (S3 event notification) is misconfigured.
Why it's wrong here
Trigger works; function is invoked.
✗
The S3 bucket policy does not grant the Lambda function write access.
Why it's wrong here
Bucket policy is not required if the execution role has permissions.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Identify which DVA-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.
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's execution role does not have an IAM policy that allows s3:PutObject. — Option D is correct because the Lambda function needs an execution role with permissions to write to S3. The resource-based policy only allows S3 to invoke the function, not the function to write. Option A is wrong because bucket policy is not needed if the execution role has permissions. Option B is wrong because the function can be triggered correctly. Option C is wrong because VPC does not cause access denied.
What should I do if I get this DVA-C02 question wrong?
Identify which DVA-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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Question Discussion
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