The answer is that the bucket policy grants access to the member account's root user ARN, but the assumed IAM role session has a completely different ARN. When a developer assumes a role, AWS STS generates a session ARN like `arn:aws:sts::123456789012:assumed-role/DevRole/session`, which does not match the root user ARN (`arn:aws:iam::123456789012:root`) specified in the bucket policy's Principal element. This is why S3 bucket policy root user access fails with IAM role—the policy explicitly restricts the principal to the root user, so any role-based session is denied by default. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of how AWS evaluates principal ARNs in resource-based policies versus identity-based policies, and it often appears as a trap where candidates assume root user grants cover all identities in the account. A helpful memory tip: "Root is a specific principal, not a blanket pass—roles get their own ARN class."
SAP-C02 Practice Question: Design Solutions for Organizational Complexity
This SAP-C02 practice question tests your understanding of design solutions for organizational complexity. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 company is using AWS Organizations with a set of member accounts that need to access a shared Amazon S3 bucket in the master account. The bucket policy allows access only from the member accounts' root user. However, developers in member accounts are unable to access the bucket even when they assume an IAM role. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The bucket policy grants access to the member account root user ARN, but the role session has a different ARN.
The bucket policy explicitly grants access to the member account's root user ARN (e.g., `arn:aws:iam::123456789012:root`). When a developer assumes an IAM role in the member account, the resulting session has a different ARN (e.g., `arn:aws:sts::123456789012:assumed-role/DevRole/session`). Because the bucket policy's Principal is restricted to the root user ARN, the role session is not recognized as a matching principal, and access is denied. This is a common misconfiguration when mixing root user grants with assumed-role access.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The bucket is encrypted with an AWS KMS key that the role does not have permissions to use.
Why it's wrong here
No encryption is mentioned; the issue is likely the principal in the bucket policy.
✗
The bucket policy requires an explicit Deny for all principals except the root user.
Why it's wrong here
Bucket policies do not require explicit Deny; they can allow specific principals.
✗
A service control policy (SCP) is denying access to the S3 bucket.
Why it's wrong here
No SCP is mentioned; SCPs would affect all actions, not just bucket access.
✓
The bucket policy grants access to the member account root user ARN, but the role session has a different ARN.
Why this is correct
When a user assumes a role, the principal becomes the role's ARN, not the root user.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume that granting access to a member account's root user automatically grants access to all IAM users and roles in that account, but in reality, root user ARN is a specific principal that does not cover assumed-role sessions or IAM users unless explicitly included.
Detailed technical explanation
How to think about this question
When an IAM role is assumed, AWS STS generates a temporary session with an ARN in the format `arn:aws:sts::account-id:assumed-role/role-name/session-name`. This ARN is distinct from the root user ARN (`arn:aws:iam::account-id:root`). S3 bucket policies evaluate the Principal element against the requester's ARN; if the policy specifies only the root user ARN, any assumed-role or IAM user ARN will not match, resulting in an implicit Deny. This behavior is fundamental to AWS's resource-based policy evaluation, where the Principal must exactly match the identity used to sign the request.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Design Solutions for Organizational Complexity — This question tests Design Solutions for Organizational Complexity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The bucket policy grants access to the member account root user ARN, but the role session has a different ARN. — The bucket policy explicitly grants access to the member account's root user ARN (e.g., `arn:aws:iam::123456789012:root`). When a developer assumes an IAM role in the member account, the resulting session has a different ARN (e.g., `arn:aws:sts::123456789012:assumed-role/DevRole/session`). Because the bucket policy's Principal is restricted to the root user ARN, the role session is not recognized as a matching principal, and access is denied. This is a common misconfiguration when mixing root user grants with assumed-role access.
What should I do if I get this SAP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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