The answer is to remove the Deny statement from the IAM policy. This is correct because of IAM policy evaluation logic: an explicit deny always overrides any allow, regardless of the order in which the policies are evaluated. Even if the role has an allow statement granting s3:GetObject access to the bucket, the explicit deny targeting that same bucket makes the read operation impossible. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this concept tests your understanding of the fundamental “deny override allow” rule, often appearing in scenarios where a SageMaker notebook role or Lambda execution role is blocked from accessing S3 data. A common trap is assuming you can add another allow statement to override the deny—this will never work. The only way to fix it is to remove or modify the explicit deny. Memory tip: “Deny is the final word—once it’s written, no allow can be smitten.”
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.
A company uses an Amazon SageMaker notebook to train a model using data from an S3 bucket. The IAM role attached to the notebook has the following policy. What is the MOST specific change needed to allow the notebook to read from the bucket 'ml-data-123'?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Remove the Deny statement from the IAM policy.
Option A is correct because the existing policy denies access to the specific bucket, so the explicit deny must be removed. Option B is wrong because the AllowedPrincipal is not required for S3 bucket policies. Option C is wrong because S3 access points are not necessary. Option D is wrong because an explicit allow cannot override an explicit deny.
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.
✗
Add an Allow statement for 's3:GetObject' on 'ml-data-123' to the IAM policy.
Why it's wrong here
Explicit denies take precedence over allows; adding an allow does not remove the deny.
✓
Remove the Deny statement from the IAM policy.
Why this is correct
An explicit deny overrides any allow; removing the deny allows the existing S3 actions to work.
Related concept
Standard ACLs match source addresses.
✗
Create an S3 access point and update the IAM policy to use the access point ARN.
Why it's wrong here
Access points provide granular access but do not override explicit denies in IAM.
✗
Add a bucket policy on 'ml-data-123' that grants access to the notebook's IAM role.
Why it's wrong here
The IAM role already has a Deny; adding a bucket policy does not override the explicit deny.
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: Remove the Deny statement from the IAM policy. — Option A is correct because the existing policy denies access to the specific bucket, so the explicit deny must be removed. Option B is wrong because the AllowedPrincipal is not required for S3 bucket policies. Option C is wrong because S3 access points are not necessary. Option D is wrong because an explicit allow cannot override an explicit deny.
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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