The correct answer is that the Deny statement with the condition explicitly blocks access to the 'confidential' prefix for any principal outside account 123456789012. This occurs because IAM policy evaluation logic prioritizes explicit Deny over any Allow—even if the team’s role has an Allow statement for S3 actions, the Deny condition checking the `aws:PrincipalAccount` against the specified account ID triggers a hard block for any cross-account access to that prefix. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this scenario tests your understanding of how IAM policy conditions interact with cross-account S3 access, a common trap where candidates overlook that a Deny with a condition still overrides all Allows for non-matching accounts. Remember the mnemonic: “Deny first, condition last—if your account’s not listed, your access is past.”
MLS-C01 Data Engineering Practice Question
This MLS-C01 practice question tests your understanding of data engineering. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 team's role. The team needs to upload data to the 'confidential' prefix in the 'my-data-lake' bucket. However, they are receiving 'AccessDenied' errors. 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 with the condition explicitly denies access to the 'confidential' prefix for accounts other than 123456789012.
Option A is correct. The Deny statement denies all s3 actions on the confidential prefix for any principal account that is not 123456789012. If the team's role is from a different account (e.g., 111111111111), the Deny applies. Option B is incorrect because the Deny has a condition, but it still denies for other accounts. Option C is incorrect because the Allow statement does not include the confidential prefix explicitly; however, the Deny overrides the Allow. Option D is incorrect because the condition does not require the team to use a specific source IP.
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 condition in the Deny statement requires the team to use a specific source IP address.
Why it's wrong here
The condition uses aws:PrincipalAccount, not source IP.
✗
The Allow statement only grants GetObject and PutObject, but the team needs ListBucket.
Why it's wrong here
The error is AccessDenied for PutObject, which is allowed in the Allow statement, but the Deny overrides it.
✓
The Deny statement with the condition explicitly denies access to the 'confidential' prefix for accounts other than 123456789012.
Why this is correct
The Deny statement applies to all actions on the confidential prefix for accounts not matching 123456789012, overriding the Allow.
Related concept
Standard ACLs match source addresses.
✗
The Allow statement's resource does not include the 'confidential' prefix.
Why it's wrong here
The Allow statement includes all objects under my-data-lake, including confidential, but the Deny overrides.
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 with the condition explicitly denies access to the 'confidential' prefix for accounts other than 123456789012. — Option A is correct. The Deny statement denies all s3 actions on the confidential prefix for any principal account that is not 123456789012. If the team's role is from a different account (e.g., 111111111111), the Deny applies. Option B is incorrect because the Deny has a condition, but it still denies for other accounts. Option C is incorrect because the Allow statement does not include the confidential prefix explicitly; however, the Deny overrides the Allow. Option D is incorrect because the condition does not require the team to use a specific source IP.
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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