The answer is to add a bucket policy that grants access to the other account's IAM role. This is the simplest and most secure method because a bucket policy uses a principal ARN to explicitly authorize a specific IAM role from the external account, allowing that role to perform actions like GetObject on the bucket without making the data public. On the AWS Certified Data Engineer Associate DEA-C01 exam, this concept tests your understanding of resource-based policies versus identity-based policies, and a common trap is confusing cross-account access with making objects public or relying solely on ACLs. Remember, bucket policies are evaluated at the resource level and can directly grant access to a trusted principal in another account, while ACLs are legacy and less flexible. A useful memory tip is "policy for the bucket, role for the user" — the bucket policy names the external role, and that role must have matching permissions in its own account.
DEA-C01 Data Security and Governance Practice Question
This DEA-C01 practice question tests your understanding of data security and governance. 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 share a dataset stored in Amazon S3 with another AWS account. The bucket policy currently grants access only to the owning account. What is the simplest way to grant cross-account access?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a bucket policy that grants access to the other account's IAM role
Option C is correct because a bucket policy with a principal ARN of the other account's IAM role is the standard way to grant cross-account access. Option A is wrong because that would make the object public, which is not recommended. Option B is wrong because a bucket policy can directly grant cross-account access without needing an IAM role in the other account. Option D is wrong because an ACL grants basic permissions but is less flexible.
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 a bucket policy that grants access to the other account's IAM role
Why this is correct
A bucket policy can specify a principal from another account.
Related concept
Standard ACLs match source addresses.
✗
Set the object ACL to public-read
Why it's wrong here
This would make the object publicly accessible, not secure.
✗
Use an S3 access control list (ACL) to grant access to the other account
Why it's wrong here
ACLs are legacy and less secure; bucket policy is preferred.
✗
Create an IAM role in the other account and attach a policy to it
Why it's wrong here
The bucket policy must also allow access; this is not sufficient alone.
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 Security and Governance — This question tests Data Security and Governance — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Add a bucket policy that grants access to the other account's IAM role — Option C is correct because a bucket policy with a principal ARN of the other account's IAM role is the standard way to grant cross-account access. Option A is wrong because that would make the object public, which is not recommended. Option B is wrong because a bucket policy can directly grant cross-account access without needing an IAM role in the other account. Option D is wrong because an ACL grants basic permissions but is less flexible.
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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