The answer is to use a bucket policy that grants the partner’s IAM role least-privilege access to the required prefix. This is the most secure and scalable pattern for cross-account S3 bucket access because a resource-based bucket policy allows you to specify the partner’s AWS account ID in the Principal element, establishing a direct trust relationship without exposing the bucket publicly or requiring custom scripts. AWS handles the cross-account authorization automatically, and by scoping access to a specific prefix, you adhere to least privilege while avoiding the operational overhead of managing IAM users or rotating keys. On the SAA-C03 exam, this scenario tests your understanding of when to use resource-based policies versus identity-based policies for cross-account access; a common trap is choosing to create an IAM user in your account and share credentials, which violates security best practices and requires manual key rotation. Memory tip: think “bucket policy for cross-account, IAM policy for same-account” — the bucket is the resource, so the policy goes on the bucket.
SAA-C03 Design Secure Architectures Practice Question
This SAA-C03 practice question tests your understanding of design secure architectures. 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. A key principle to apply: s3 bucket policies are resource-based policies attached directly to an S3 bucket.. 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 partner company needs read-only access to reports in an S3 bucket for a e-learning platform. The partner has its own AWS account. What is the most secure scalable access pattern? The design must avoid adding custom operational scripts.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a bucket policy that grants the partner role least-privilege access to the required prefix
Option C is correct because it uses a resource-based bucket policy that grants the partner's IAM role cross-account read-only access to a specific prefix, adhering to the principle of least privilege. This approach is secure (no public exposure), scalable (no manual key rotation), and requires no custom scripts, as AWS handles the cross-account trust automatically via the bucket policy's Principal element referencing the partner's AWS account ID.
Key principle: S3 bucket policies are resource-based policies attached directly to an S3 bucket.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Copy the objects to a public website bucket
Why it's wrong here
A public website bucket exposes data unnecessarily.
✗
Create an IAM user in the company account and share the access keys
Why it's wrong here
Long-term shared credentials are less secure and harder to govern.
✓
Create a bucket policy that grants the partner role least-privilege access to the required prefix
Why this is correct
A resource policy can grant cross-account access to a specific external role and prefix.
Related concept
S3 bucket policies are resource-based policies attached directly to an S3 bucket.
✗
Make the objects public and rely on difficult-to-guess object names
Why it's wrong here
Security through obscurity is not an access-control strategy.
Common exam traps
Common exam trap: answer the scenario, not the keyword
AWS often tests the misconception that sharing IAM user access keys is acceptable for cross-account access, but the trap here is that IAM users are for human identities within the same account, not for secure cross-account automation, and bucket policies with IAM roles are the recommended pattern for least-privilege, script-free access.
Detailed technical explanation
How to think about this question
Cross-account bucket policies use the Principal element with the partner's AWS account ID (e.g., "Principal": {"AWS": "arn:aws:iam::PARTNER_ACCOUNT_ID:root"}) and a Condition key like "aws:SourceArn" to prevent confused deputy attacks. The partner then attaches an IAM role with a trust policy allowing the bucket's account to assume it, and the bucket policy grants s3:GetObject on the specific prefix (e.g., "arn:aws:s3:::bucket-name/reports/*"). This eliminates the need for access keys or scripts, as AWS STS handles temporary credential exchange.
KKey Concepts to Remember
S3 bucket policies are resource-based policies attached directly to an S3 bucket.
Bucket policies support cross-account access by granting permissions to external AWS account IDs or roles.
Least privilege is enforced by specifying actions (e.g., `s3:GetObject`) and resource prefixes.
The partner's IAM role must have a trust policy allowing the company's account to assume it.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
S3 bucket policies are resource-based policies attached directly to an S3 bucket.
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 s3 bucket policies are resource-based policies attached directly to an S3 bucket., then practise related SAA-C03 questions on the same topic to reinforce the concept.
Design Secure Architectures — This question tests Design Secure Architectures — S3 bucket policies are resource-based policies attached directly to an S3 bucket..
What is the correct answer to this question?
The correct answer is: Create a bucket policy that grants the partner role least-privilege access to the required prefix — Option C is correct because it uses a resource-based bucket policy that grants the partner's IAM role cross-account read-only access to a specific prefix, adhering to the principle of least privilege. This approach is secure (no public exposure), scalable (no manual key rotation), and requires no custom scripts, as AWS handles the cross-account trust automatically via the bucket policy's Principal element referencing the partner's AWS account ID.
What should I do if I get this SAA-C03 question wrong?
Review s3 bucket policies are resource-based policies attached directly to an S3 bucket., then practise related SAA-C03 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
S3 bucket policies are resource-based policies attached directly to an S3 bucket.
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