The answer is a modified S3 bucket policy that denies write access to the Glue job's IAM role. AWS Glue ETL jobs assume an IAM role to interact with S3, and even if the role itself has full S3 permissions, an explicit deny in the bucket policy overrides any allow, causing the Access Denied error. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of how IAM policies and resource-based policies interact—a common trap is confusing insufficient memory or encryption key issues with straightforward permission denials. Remember that Access Denied on S3 almost always points to a permissions boundary, not resource constraints. Memory tip: "Deny always wins"—when troubleshooting AWS Glue Access Denied errors on S3, always check the bucket policy first for explicit denies before looking at the IAM role.
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 engineering team uses AWS Glue ETL jobs to process data from Amazon S3. The jobs recently started failing with 'Access Denied' errors when writing to the output S3 bucket. 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 was modified to deny write access to the Glue job's IAM role.
Option C is correct because AWS Glue ETL jobs require an IAM role with permissions to write to the S3 bucket. If the bucket policy was inadvertently changed to deny access to that role, the job would fail. Option A is wrong because insufficient memory would cause out-of-memory errors, not access denied. Option B is wrong because separate encryption permissions are not the primary cause; S3 access permissions are. Option D is wrong because KMS key permissions would cause encryption-related errors, not general access denied.
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 KMS key used for server-side encryption is not accessible to the Glue job.
Why it's wrong here
KMS key issues cause specific encryption errors, not generic access denied.
✗
The S3 bucket does not have default encryption enabled.
Why it's wrong here
Lack of encryption is not an access denied issue; the job can write without encryption.
✗
The job ran out of memory due to large data volume.
Why it's wrong here
Insufficient memory causes out-of-memory errors, not access denied.
✓
The S3 bucket policy was modified to deny write access to the Glue job's IAM role.
Why this is correct
An explicit deny in the bucket policy overrides any allow in the IAM role policy.
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.
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 was modified to deny write access to the Glue job's IAM role. — Option C is correct because AWS Glue ETL jobs require an IAM role with permissions to write to the S3 bucket. If the bucket policy was inadvertently changed to deny access to that role, the job would fail. Option A is wrong because insufficient memory would cause out-of-memory errors, not access denied. Option B is wrong because separate encryption permissions are not the primary cause; S3 access permissions are. Option D is wrong because KMS key permissions would cause encryption-related errors, not general access denied.
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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