The answer is a bucket policy that grants the partner IAM role least-privilege access to a specific prefix. This is the most secure cross-account S3 access pattern because it uses a resource-based policy to explicitly delegate read-only permissions to a trusted IAM role in the partner AWS account, avoiding the need to share long-term access keys or manage external IAM users. On the SAA-C03 exam, this scenario tests your understanding of cross-account trust mechanisms and the principle of least privilege; a common trap is choosing to create a new IAM user in your account for the partner, which is less scalable and introduces credential management overhead. The key distinction is that a bucket policy paired with the partner’s existing IAM role leverages AWS’s built-in trust relationship, ensuring access is temporary and revocable. Memory tip: “Bucket policy for the role, not a user for the soul” — always delegate to an existing role in the partner account.
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 grant cross-account access to specific IAM principals.. 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?
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 AWS account (via its root user or an IAM role) least-privilege read-only access to a specific prefix. This approach avoids sharing long-term credentials, leverages AWS's cross-account trust mechanism, and scales securely without managing additional IAM users.
Key principle: S3 bucket policies grant cross-account access to specific IAM principals.
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 grant cross-account access to specific IAM principals.
✗
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
The trap here is that candidates often choose Option B (sharing IAM user credentials) because it seems straightforward, but AWS recommends cross-account roles with bucket policies for secure, auditable, and scalable access without managing external users.
Detailed technical explanation
How to think about this question
Cross-account bucket policies use the `Principal` element to specify the partner's AWS account ID (e.g., `"Principal": { "AWS": "arn:aws:iam::PARTNER_ACCOUNT_ID:root" }`), which allows the partner to assume a role in their own account to access the bucket. The policy can be scoped to a prefix using `Condition` with `s3:prefix` to enforce least privilege. Under the hood, S3 evaluates both the bucket policy and the requesting principal's IAM permissions, requiring an explicit allow from both sides.
KKey Concepts to Remember
S3 bucket policies grant cross-account access to specific IAM principals.
Cross-account access uses a 'pull' model where the external role assumes permissions.
Least privilege is enforced by specifying allowed actions (e.g., `s3:GetObject`) and resources (e.g., `arn:aws:s3:::your-bucket/reports/*`).
Sharing access keys for IAM users is a less secure practice for cross-account access.
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 grant cross-account access to specific IAM principals.
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 grant cross-account access to specific IAM principals., 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 grant cross-account access to specific IAM principals..
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 AWS account (via its root user or an IAM role) least-privilege read-only access to a specific prefix. This approach avoids sharing long-term credentials, leverages AWS's cross-account trust mechanism, and scales securely without managing additional IAM users.
What should I do if I get this SAA-C03 question wrong?
Review s3 bucket policies grant cross-account access to specific IAM principals., 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 grant cross-account access to specific IAM principals.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A partner company needs read-only access to reports in an S3 bucket for a B2B file exchange site. The partner has its own AWS account. What is the most secure scalable access pattern? The design must avoid adding custom operational scripts.
medium
A.Make the objects public and rely on difficult-to-guess object names
B.Create an IAM user in the company account and share the access keys
✓ C.Create a bucket policy that grants the partner role least-privilege access to the required prefix
D.Copy the objects to a public website bucket
Why C: Option C is correct because it uses a bucket policy with a principal ARN for the partner's AWS account, granting read-only access to a specific prefix. This is secure (no public exposure), scalable (no per-user credentials to manage), and avoids custom scripts by leveraging native AWS IAM and S3 policy evaluation. The partner can use their own IAM roles to access the bucket without sharing long-term access keys.
Variation 2. A partner company needs read-only access to reports in an S3 bucket for a customer analytics portal. The partner has its own AWS account. What is the most secure scalable access pattern?
medium
A.Make the objects public and rely on difficult-to-guess object names
✓ B.Create a bucket policy that grants the partner role least-privilege access to the required prefix
C.Copy the objects to a public website bucket
D.Create an IAM user in the company account and share the access keys
Why B: Option B is correct because a bucket policy that grants the partner's IAM role (from the partner's AWS account) least-privilege access to a specific prefix is the most secure and scalable pattern. This uses cross-account IAM roles, avoiding long-term credentials and allowing the partner to manage their own users and permissions. The bucket policy explicitly trusts the partner's AWS account, and the partner assumes the role to access only the required objects, following the principle of least privilege.
Variation 3. A partner company needs read-only access to reports in an S3 bucket for a image sharing application. The partner has its own AWS account. What is the most secure scalable access pattern?
medium
A.Make the objects public and rely on difficult-to-guess object names
B.Create an IAM user in the company account and share the access keys
C.Copy the objects to a public website bucket
✓ D.Create a bucket policy that grants the partner role least-privilege access to the required prefix
Why D: Option D is correct because it uses a resource-based bucket policy that grants the partner's AWS account (via its IAM role) least-privilege read-only access to a specific prefix. This avoids sharing long-term credentials, leverages AWS's cross-account trust mechanism, and ensures the partner's access is controlled through their own IAM roles, which is the most secure and scalable pattern for cross-account S3 access.
Variation 4. A partner company needs read-only access to reports in an S3 bucket for a B2B file exchange site. The partner has its own AWS account. What is the most secure scalable access pattern?
medium
A.Make the objects public and rely on difficult-to-guess object names
B.Create an IAM user in the company account and share the access keys
✓ C.Create a bucket policy that grants the partner role least-privilege access to the required prefix
D.Copy the objects to a public website bucket
Why C: Option C is correct because it uses a resource-based bucket policy that grants the partner's IAM role (from their own AWS account) least-privilege read-only access to a specific prefix. This avoids sharing long-term credentials, follows the principle of cross-account access using IAM roles and bucket policies, and is fully scalable without managing external users.
Variation 5. A partner company needs read-only access to reports in an S3 bucket for a financial reporting platform. The partner has its own AWS account. What is the most secure scalable access pattern?
medium
✓ A.Create a bucket policy that grants the partner role least-privilege access to the required prefix
B.Create an IAM user in the company account and share the access keys
C.Copy the objects to a public website bucket
D.Make the objects public and rely on difficult-to-guess object names
Why A: Option A is correct because a bucket policy with a condition that grants read-only access to a specific prefix allows the partner's AWS account to access the S3 bucket without creating IAM users or sharing long-term credentials. This leverages cross-account IAM roles, where the partner assumes a role in their own account that the bucket policy trusts, ensuring least-privilege access and eliminating the need to manage static keys. The policy can be scoped to a specific prefix (e.g., `reports/`) and use the `aws:SourceArn` or `aws:SourceAccount` condition key to restrict access to only the partner's account, providing both security and scalability.
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