The correct answer is to enable S3 Block Public Access settings on the bucket and to use a bucket policy that explicitly denies public access. These two measures work together to prevent public access to Amazon S3 buckets by overriding any permissions that might otherwise allow anonymous or authenticated AWS users from outside the account to read or write objects. Block Public Access acts as a safety catch at the account and bucket level, while a deny-effect bucket policy provides a granular, explicit control that cannot be overridden by other allow policies. On the AWS Certified Data Engineer Associate DEA-C01 exam, this topic tests your understanding of defense-in-depth for data security, often appearing in scenario-based questions where you must distinguish between access controls and unrelated features like encryption or versioning. A common trap is confusing server-side encryption with access control—encryption protects data at rest but does not block public read or write access. Remember the mnemonic “BPD” for Bucket Policy and Deny to keep public access away.
DEA-C01 Data Operations and Support Practice Question
This DEA-C01 practice question tests your understanding of data operations and support. 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.
A data engineer needs to ensure that data in an Amazon S3 bucket is not publicly accessible. Which TWO measures should the engineer implement? (Choose TWO.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Attach a bucket policy that denies access to 'Principal': '*' unless specific conditions are met.
Blocking public access at the bucket level and using bucket policies to deny public access are effective controls. Option C is wrong because encryption does not prevent public access. Option D is wrong because versioning does not control access. Option E is wrong because lifecycle policies do not control access.
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.
✓
Attach a bucket policy that denies access to 'Principal': '*' unless specific conditions are met.
Why this is correct
A bucket policy can deny all public access.
Related concept
Standard ACLs match source addresses.
✗
Create a lifecycle policy to delete objects after 30 days.
Why it's wrong here
Lifecycle policies manage object expiration, not access control.
✓
Enable S3 Block Public Access settings on the bucket.
Why this is correct
This setting explicitly blocks any public access.
Related concept
Standard ACLs match source addresses.
✗
Enable S3 Versioning on the bucket.
Why it's wrong here
Versioning protects against overwrites, not public access.
✗
Enable default encryption on the bucket.
Why it's wrong here
Encryption protects data at rest but does not affect public access.
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: Attach a bucket policy that denies access to 'Principal': '*' unless specific conditions are met. — Blocking public access at the bucket level and using bucket policies to deny public access are effective controls. Option C is wrong because encryption does not prevent public access. Option D is wrong because versioning does not control access. Option E is wrong because lifecycle policies do not control access.
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.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Question Discussion
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