The answer is s3:ListBucket, which is the missing permission causing your AWS Glue job to fail with an AccessDenied error when writing to S3. While the IAM policy attached to the Glue service role grants s3:GetObject and s3:PutObject on the bucket’s objects, it omits the s3:ListBucket action on the bucket itself. Many Glue operations, such as discovering existing partitions or validating the target path, require ListBucket to enumerate objects in the bucket before writing. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this scenario tests your understanding of how S3 permissions interact with Glue’s underlying read-before-write behavior—a common trap is assuming PutObject alone is sufficient for writing. Remember the memory tip: “To write, you must first see the bucket’s key.”
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. A data engineer is troubleshooting an AWS Glue job that fails with an 'AccessDenied' error when trying to write to the S3 bucket 'my-data-lake'. The IAM policy attached to the Glue service role is shown. What is the missing permission?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
s3:ListBucket
The policy allows s3:GetObject and s3:PutObject on the bucket's objects, but it does not allow s3:ListBucket on the bucket itself. Many Glue operations require ListBucket to discover objects. Option D (s3:ListBucket) is missing. Option A (s3:DeleteObject) is not needed. Option B (s3:GetBucketLocation) is not required. Option C (s3:PutObjectAcl) is not needed.
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.
✓
s3:ListBucket
Why this is correct
Correct: Glue needs ListBucket to list objects in the bucket.
Related concept
Standard ACLs match source addresses.
✗
s3:PutObjectAcl
Why it's wrong here
Incorrect: Not needed unless setting ACLs.
✗
s3:GetBucketLocation
Why it's wrong here
Incorrect: Not required for write operations.
✗
s3:DeleteObject
Why it's wrong here
Incorrect: Delete is not needed for writing.
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: s3:ListBucket — The policy allows s3:GetObject and s3:PutObject on the bucket's objects, but it does not allow s3:ListBucket on the bucket itself. Many Glue operations require ListBucket to discover objects. Option D (s3:ListBucket) is missing. Option A (s3:DeleteObject) is not needed. Option B (s3:GetBucketLocation) is not required. Option C (s3:PutObjectAcl) is not needed.
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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