The answer is that access is denied because the explicit deny in the S3 bucket policy overrides the allow from the IAM role. This outcome is dictated by the core IAM policy evaluation logic: any explicit deny statement, regardless of which policy it appears in, takes precedence over any allow. Even though the instance’s role grants s3:GetObject, the bucket policy explicitly denies that action for the role, so the request is blocked. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this concept frequently appears in troubleshooting scenarios where a resource-based policy (like an S3 bucket policy) conflicts with an identity-based policy (like an IAM role). A common trap is assuming that an IAM role allow will always win, but the evaluation logic is clear: explicit deny is the final say. Remember the mnemonic “DENY wins the day” — no matter how many allows exist, a single explicit deny stops all access.
DOP-C02 Security and Compliance Practice Question
This DOP-C02 practice question tests your understanding of security and compliance. 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 DevOps engineer is troubleshooting an issue where an EC2 instance cannot access an S3 bucket. The instance has an IAM role attached with a policy that allows s3:GetObject. The S3 bucket policy explicitly denies access to the instance's role. What is the result?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Access is denied because the bucket policy explicitly denies
An explicit deny in any policy overrides any allow. The bucket policy deny takes precedence over the IAM role allow, so access is denied. Evaluation logic is that an explicit deny prevents 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.
✗
Access is denied only if the bucket is encrypted
Why it's wrong here
Encryption does not affect IAM policy evaluation.
✗
Access is allowed only if the instance is in the same region
Why it's wrong here
Region does not affect this evaluation.
✗
Access is allowed because the IAM role allows it
Why it's wrong here
An explicit deny overrides any allow.
✓
Access is denied because the bucket policy explicitly denies
Why this is correct
The explicit deny in the bucket policy takes precedence over the allow.
Related concept
Standard ACLs match source addresses.
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 DOP-C02 ACL questions on filtering logic and placement.
Security and Compliance — This question tests Security and Compliance — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Access is denied because the bucket policy explicitly denies — An explicit deny in any policy overrides any allow. The bucket policy deny takes precedence over the IAM role allow, so access is denied. Evaluation logic is that an explicit deny prevents access.
What should I do if I get this DOP-C02 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 DOP-C02 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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