- A
Add an S3 bucket policy on Account A's bucket with Principal set to Account B's account ID and s3:GetObject permission; ensure Account B's roles have s3:GetObject in their identity policies
Cross-account S3 access requires both a resource-based policy (bucket policy) that grants Account B access, and identity-based policies in Account B that allow the action. The bucket policy's Principal field specifies Account B's account root ARN or specific role ARNs. When both sides allow, the call succeeds without any role chaining or credential sharing.
- B
Create an IAM role in Account A with s3:GetObject permission and a trust policy allowing Account B's roles to assume it
Why wrong: This approach works (role chaining) but requires Account B's services to call sts:AssumeRole before each S3 operation, adding latency and complexity. The question asks for access without requiring Account B to assume a role in Account A.
- C
Generate a presigned URL for each object in Account A and share the URLs with Account B's services
Why wrong: Presigned URLs expire and must be regenerated regularly. They are appropriate for temporary, unauthenticated object access (e.g., browser downloads) but are not suitable for an ongoing programmatic access pattern where Account B's services read many objects on demand.
- D
Enable S3 Access Points on the bucket and create an access point that allows Account B's VPC to connect via PrivateLink
Why wrong: S3 Access Points simplify access management for large shared datasets and can restrict access to specific VPCs. However, cross-account access through an access point still requires a bucket policy delegation to the access point and a VPC endpoint setup — more configuration than a direct bucket policy grant, and PrivateLink is not strictly required for cross-account S3 access.
Quick Answer
The answer is to add an S3 bucket policy on Account A’s bucket with the Principal set to Account B’s account ID and the s3:GetObject permission, while ensuring Account B’s IAM roles also have s3:GetObject in their identity policies. This works because cross-account S3 bucket policy access relies on a resource-based policy that explicitly names the external account as the principal, granting permission to all IAM principals within that account. For the access to be effective, Account B’s roles must still have an identity-based policy allowing the same action, creating a two-way authorization check. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your understanding of the difference between resource-based and identity-based policies, and a common trap is forgetting that both policies must allow the action—the bucket policy alone is insufficient. A helpful memory tip is “bucket policy for the door, identity policy for the key”: the bucket policy opens the door to the external account, but each role still needs its own key (identity policy) to walk through.
SOA-C02 Practice Question: S3 bucket policy for cross-account read access…
This SOA-C02 practice question tests your understanding of security and compliance. 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. A key principle to apply: s3 bucket policy. 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.
Account A owns an S3 bucket containing shared artifacts. Account B needs to read objects from the bucket. The Account A team wants to grant access without creating IAM users, sharing access keys, or creating a role in Account A that Account B assumes. How should the bucket be configured to allow Account B's IAM roles to read objects?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Add an S3 bucket policy on Account A's bucket with Principal set to Account B's account ID and s3:GetObject permission; ensure Account B's roles have s3:GetObject in their identity policies
Option A is correct because it uses an S3 bucket policy with a Principal set to Account B's account ID, which grants cross-account access to all IAM principals (users and roles) in Account B. Account B's IAM roles must also have an identity policy that allows s3:GetObject, ensuring that the effective permissions require both the bucket policy and the role's policy to allow the action. This approach avoids creating IAM users, sharing access keys, or setting up a role in Account A for Account B to assume.
Key principle: S3 bucket policy
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 an S3 bucket policy on Account A's bucket with Principal set to Account B's account ID and s3:GetObject permission; ensure Account B's roles have s3:GetObject in their identity policies
Why this is correct
Cross-account S3 access requires both a resource-based policy (bucket policy) that grants Account B access, and identity-based policies in Account B that allow the action. The bucket policy's Principal field specifies Account B's account root ARN or specific role ARNs. When both sides allow, the call succeeds without any role chaining or credential sharing.
Related concept
S3 bucket policy
- ✗
Create an IAM role in Account A with s3:GetObject permission and a trust policy allowing Account B's roles to assume it
Why it's wrong here
This approach works (role chaining) but requires Account B's services to call sts:AssumeRole before each S3 operation, adding latency and complexity. The question asks for access without requiring Account B to assume a role in Account A.
- ✗
Generate a presigned URL for each object in Account A and share the URLs with Account B's services
Why it's wrong here
Presigned URLs expire and must be regenerated regularly. They are appropriate for temporary, unauthenticated object access (e.g., browser downloads) but are not suitable for an ongoing programmatic access pattern where Account B's services read many objects on demand.
- ✗
Enable S3 Access Points on the bucket and create an access point that allows Account B's VPC to connect via PrivateLink
Why it's wrong here
S3 Access Points simplify access management for large shared datasets and can restrict access to specific VPCs. However, cross-account access through an access point still requires a bucket policy delegation to the access point and a VPC endpoint setup — more configuration than a direct bucket policy grant, and PrivateLink is not strictly required for cross-account S3 access.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a bucket policy with a cross-account Principal automatically grants access to all IAM roles in that account, but candidates forget that the roles must also have an explicit allow in their identity policies for the action to succeed.
Detailed technical explanation
How to think about this question
When using a bucket policy with a cross-account Principal, AWS evaluates both the bucket policy and the requesting principal's identity policy; the request is allowed only if both policies grant the action (unless the bucket policy explicitly allows the account's root principal). This is an example of the 'intersection' model for cross-account S3 access, where the bucket policy must specify the external account ID (not an IAM role ARN) to grant access to all IAM principals in that account. In practice, this is commonly used for shared data lakes where multiple accounts need read access to a central bucket without managing roles or keys.
KKey Concepts to Remember
- S3 bucket policy
- cross-account access
- Principal account ID
- resource-based policy
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 policy
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 policy, then practise related SOA-C02 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this SOA-C02 question test?
Security and Compliance — This question tests Security and Compliance — S3 bucket policy.
What is the correct answer to this question?
The correct answer is: Add an S3 bucket policy on Account A's bucket with Principal set to Account B's account ID and s3:GetObject permission; ensure Account B's roles have s3:GetObject in their identity policies — Option A is correct because it uses an S3 bucket policy with a Principal set to Account B's account ID, which grants cross-account access to all IAM principals (users and roles) in Account B. Account B's IAM roles must also have an identity policy that allows s3:GetObject, ensuring that the effective permissions require both the bucket policy and the role's policy to allow the action. This approach avoids creating IAM users, sharing access keys, or setting up a role in Account A for Account B to assume.
What should I do if I get this SOA-C02 question wrong?
Review s3 bucket policy, then practise related SOA-C02 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
S3 bucket policy
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Last reviewed: Jun 11, 2026
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