The answer is the missing s3:PutObjectAcl permission. When a Lambda function writes encrypted objects to an S3 bucket, the s3:PutObject action alone is insufficient if the bucket policy or encryption settings require explicit ACL control over the object. The AccessDenied error occurs because the IAM policy grants s3:PutObject but omits s3:PutObjectAcl, which is necessary when the bucket enforces bucket-owner-full-control ACLs or when server-side encryption with AWS KMS (SSE-KMS) is used, as the Lambda function must also set the ACL during the put operation. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of how S3 permissions interact with encryption contexts—a common trap is assuming s3:PutObject covers all write operations. Remember the memory tip: "PutObject writes, PutObjectAcl rights"—without the ACL permission, encrypted puts fail.
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 attached the above IAM policy to an AWS Lambda function that writes encrypted objects to an S3 bucket. The function fails with an 'AccessDenied' error when putting objects. 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 policy does not include s3:PutObjectAcl permission.
Option C is correct because the policy allows s3:PutObject but does not include s3:PutObjectAcl or other permissions that may be needed by the Lambda function or the encryption context. Option A is wrong because the policy is not missing; it is there. Option B is wrong because KMS permissions are granted. Option D is wrong because s3:GetObject is not needed for writing; but missing s3:PutObjectAcl is common when bucket policies enforce specific ACLs.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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 policy does not include s3:PutObjectAcl permission.
Why this is correct
If the bucket requires object ACLs, the function needs s3:PutObjectAcl.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The policy is missing a statement for the S3 bucket itself (not the objects).
Why it's wrong here
The Resource includes the bucket ARN with /* for objects; bucket-level permission is not needed for PutObject.
✗
The policy allows s3:GetObject, which is unnecessary and conflicts with PutObject.
Why it's wrong here
Having s3:GetObject does not cause access denied on PutObject.
✗
The KMS key policy does not allow the Lambda function to decrypt.
Why it's wrong here
The policy grants kms:Decrypt and kms:GenerateDataKey*.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related DVA-C02 ACL questions on filtering logic and placement.
Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The policy does not include s3:PutObjectAcl permission. — Option C is correct because the policy allows s3:PutObject but does not include s3:PutObjectAcl or other permissions that may be needed by the Lambda function or the encryption context. Option A is wrong because the policy is not missing; it is there. Option B is wrong because KMS permissions are granted. Option D is wrong because s3:GetObject is not needed for writing; but missing s3:PutObjectAcl is common when bucket policies enforce specific ACLs.
What should I do if I get this DVA-C02 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related DVA-C02 ACL questions on filtering logic and placement.
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?
Standard ACLs match source addresses.
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