The answer is the S3 bucket policy denying access to the Glue job’s IAM role. This is because, in AWS, an explicit deny in a resource-based policy like an S3 bucket policy overrides any allow granted by an identity-based policy such as an IAM role, even when the role has full S3 permissions. For the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of the policy evaluation logic—specifically that bucket policies are evaluated separately from IAM policies, and an explicit deny always wins. A common trap is assuming that if the IAM role allows access, the operation will succeed, but bucket policies can silently block reads or writes. To remember this, think: “IAM says yes, bucket says no—deny wins, and Glue can’t go.”
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 data pipeline uses AWS Glue to process data from Amazon S3 and write results to Amazon Redshift. The pipeline fails intermittently with the error 'S3ServiceException: Access Denied'. The IAM role used by Glue has permissions to read from the S3 bucket. What is the most likely cause of this error?
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 Glue job's IAM role
Option C is correct because S3 bucket policies can explicitly deny access even if the IAM role allows it. Option A is wrong because S3 Transfer Acceleration is not related to access denied errors. Option B is wrong because S3 is not region-specific for the error. Option D is wrong because S3 Server Access Logging does not affect access permissions.
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 S3 bucket is in a different AWS Region than the Glue job
Why it's wrong here
Cross-region access is allowed if permissions are correct.
✗
S3 Server Access Logging is enabled and blocking requests
Why it's wrong here
Server Access Logging does not block access.
✓
The S3 bucket policy denies access to the Glue job's IAM role
Why this is correct
A bucket policy can explicitly deny access, overriding IAM allow.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The S3 bucket has S3 Transfer Acceleration enabled
Why it's wrong here
Transfer Acceleration does not cause access denied errors.
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 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 Glue job's IAM role — Option C is correct because S3 bucket policies can explicitly deny access even if the IAM role allows it. Option A is wrong because S3 Transfer Acceleration is not related to access denied errors. Option B is wrong because S3 is not region-specific for the error. Option D is wrong because S3 Server Access Logging does not affect access permissions.
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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