The answer is the S3 bucket policy denying access to the Redshift cluster’s IP addresses. Even when the IAM role attached to Redshift grants full S3 permissions, an explicit Deny in the bucket policy—such as one restricting access to a specific IP range—will override that allow, causing the COPY command to fail with an Access Denied error. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of the AWS policy evaluation logic, where explicit Denies in resource-based policies (like S3 bucket policies) always take precedence over identity-based permissions. A common trap is assuming the IAM role is the only factor, but bucket policies act as an additional gatekeeper. Remember the memory tip: “Role allows, bucket denies—COPY dies.” Always check both the IAM role and the S3 bucket policy when diagnosing intermittent access issues.
DEA-C01 Data Operations and Support Practice Question
This DEA-C01 practice question tests your understanding of data operations and support. 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 is using Amazon Redshift for its data warehouse. A data engineer notices that COPY commands from S3 are failing intermittently with 'S3ServiceException: Access Denied'. The IAM role used by Redshift has the correct permissions. 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 S3 bucket policy denies access to the Redshift cluster's IP addresses.
Option D is correct because S3 bucket policies may deny access even if the role allows it. Option A is wrong because the role is already attached. Option B is wrong because encryption would cause different errors. Option C is wrong because if the role exists, it should work; the issue is likely external.
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 IAM role is not attached to the Redshift cluster.
Why it's wrong here
The scenario states the role has correct permissions, implying it's attached.
✗
The S3 bucket uses SSE-KMS encryption and the role lacks kms:Decrypt.
Why it's wrong here
This would result in a KMS error, not S3 Access Denied.
✗
The IAM role name contains a typo in the COPY command.
Why it's wrong here
A typo would cause a 'role does not exist' error, not Access Denied.
✓
The S3 bucket policy denies access to the Redshift cluster's IP addresses.
Why this is correct
Bucket policies can override IAM permissions and cause Access Denied.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
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.
Trap categories for this question
Scenario analysis trap
The scenario states the role has correct permissions, implying it's attached.
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 DEA-C01 ACL questions on filtering logic and placement.
Data Operations and Support — This question tests Data Operations and Support — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The S3 bucket policy denies access to the Redshift cluster's IP addresses. — Option D is correct because S3 bucket policies may deny access even if the role allows it. Option A is wrong because the role is already attached. Option B is wrong because encryption would cause different errors. Option C is wrong because if the role exists, it should work; the issue is likely external.
What should I do if I get this DEA-C01 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 DEA-C01 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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