The answer is that the Lambda function is missing the `kms:GenerateDataKey` permission. This is required because when writing an object to an S3 bucket encrypted with a customer-managed KMS key, the Lambda execution role must have `kms:GenerateDataKey` (or `kms:Encrypt`) to request a data key from KMS for server-side encryption. Without it, the `s3:PutObject` call succeeds at the S3 level, but the underlying KMS operation fails, resulting in an access denied error. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of how S3 and KMS permissions interact—a common trap is assuming `s3:PutObject` alone is sufficient, or misattributing the error to the key policy. Remember the memory tip: "Write needs GenerateDataKey, read needs Decrypt."
DVA-C02 Troubleshooting and Optimization Practice Question
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
The exhibit shows an IAM policy attached to a Lambda function's execution role. The function writes objects to an S3 bucket that is encrypted with a KMS key (the key specified in the policy). When the function tries to write an object, it receives an access denied error. What is the MOST likely missing permission?
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
✓
kms:GenerateDataKey is missing.
Option B is correct because to write an encrypted object, the function needs kms:GenerateDataKey or kms:Encrypt permission. Option A is wrong because s3:PutObject is allowed. Option C is wrong because KMS key policy might be restrictive, but the most direct missing permission is kms:GenerateDataKey. Option D is wrong because kms:ReEncrypt is not needed.
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.
✓
kms:GenerateDataKey is missing.
Why this is correct
S3 uses GenerateDataKey for server-side encryption with KMS.
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 KMS key policy does not allow the Lambda function role.
Why it's wrong here
Could be, but the missing permission on the role is more direct.
✗
s3:GetObject is missing for the bucket.
Why it's wrong here
s3:PutObject is allowed, and GetObject is not needed for write.
✗
kms:ReEncrypt is missing.
Why it's wrong here
ReEncrypt is not used for initial writes.
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: kms:GenerateDataKey is missing. — Option B is correct because to write an encrypted object, the function needs kms:GenerateDataKey or kms:Encrypt permission. Option A is wrong because s3:PutObject is allowed. Option C is wrong because KMS key policy might be restrictive, but the most direct missing permission is kms:GenerateDataKey. Option D is wrong because kms:ReEncrypt is not needed.
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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