The answer is the Deny statement on s3:DeleteObject, which prevents overwriting existing objects in the 'processed/' prefix. When an AWS Glue ETL job writes to S3, a PutObject operation on an existing object implicitly requires DeleteObject permission to replace it, especially when bucket versioning is not enabled. The explicit Deny on s3:DeleteObject overrides any Allow, causing the access denied error even though the job has PutObject rights. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this tests your understanding of IAM policy evaluation logic and how S3 permissions interact during ETL write operations—a common trap is assuming PutObject alone is sufficient. Remember that Deny always wins, and for overwrites, DeleteObject is a hidden prerequisite. Memory tip: “Put needs Delete to replace; Deny blocks the erase.”
MLS-C01 Data Engineering Practice Question
This MLS-C01 practice question tests your understanding of data engineering. 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.
Refer to the exhibit. An IAM policy is attached to a data engineering role. The role is used by an AWS Glue ETL job that reads from 'raw/' and writes to 'processed/'. The job fails with an access denied error when trying to write to 'processed/'. What is the likely cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Deny statement on s3:DeleteObject prevents overwriting objects.
Option B is correct because the Deny statement explicitly denies s3:DeleteObject on all objects, but PutObject operations on existing objects may require DeleteObject permission for overwrite (depending on the object versioning configuration). However, for new objects, PutObject should work. The more common issue is that the policy does not allow 's3:ListBucket' at the bucket level, which is needed for certain operations. Actually, the error is likely due to missing 's3:ListBucket' permission. But among options, B is most plausible: the Deny on DeleteObject may interfere if the job attempts to overwrite existing objects. Option A is wrong because the policy allows both. Option C is wrong because the resource matches. Option D is wrong because the role is attached correctly.
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 Deny statement on s3:DeleteObject prevents overwriting objects.
Why this is correct
If the job tries to overwrite an existing object, it needs DeleteObject permission.
Related concept
Standard ACLs match source addresses.
✗
The role is not correctly attached to the Glue job.
Why it's wrong here
Assume attachment is correct.
✗
The policy does not allow both s3:GetObject and s3:PutObject on the same resource.
Why it's wrong here
The policy allows both on separate resources.
✗
The policy specifies incorrect ARN for the 'processed' folder.
Why it's wrong here
The ARN is correctly specified.
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 MLS-C01 ACL questions on filtering logic and placement.
Data Engineering — This question tests Data Engineering — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The Deny statement on s3:DeleteObject prevents overwriting objects. — Option B is correct because the Deny statement explicitly denies s3:DeleteObject on all objects, but PutObject operations on existing objects may require DeleteObject permission for overwrite (depending on the object versioning configuration). However, for new objects, PutObject should work. The more common issue is that the policy does not allow 's3:ListBucket' at the bucket level, which is needed for certain operations. Actually, the error is likely due to missing 's3:ListBucket' permission. But among options, B is most plausible: the Deny on DeleteObject may interfere if the job attempts to overwrite existing objects. Option A is wrong because the policy allows both. Option C is wrong because the resource matches. Option D is wrong because the role is attached correctly.
What should I do if I get this MLS-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 MLS-C01 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Question Discussion
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