- A
Create an IAM role in Account B that Account A can assume through STS, then grant the role S3 permissions.
Cross-account role assumption with AWS STS is the standard way to grant temporary access without sharing long-lived credentials. By placing the permissions on a role in Account B and controlling the trust policy there, the bucket-owning account keeps central control and can revoke access by changing the trust relationship or permissions. The Lambda execution role in Account A assumes the role when needed and receives short-lived credentials only.
- B
Create an IAM user in Account B and store its access keys in Lambda environment variables.
Why wrong: Static access keys are long-lived credentials and create unnecessary operational and security risk.
- C
Attach a security group to the Lambda function that allows outbound traffic to the bucket.
Why wrong: Security groups do not grant S3 permissions, and Lambda does not use security groups as an authorization mechanism for S3 access.
- D
Use AWS Organizations SCPs to grant the Lambda function permission to write to the bucket.
Why wrong: SCPs can only restrict permissions, not grant access to a specific workload or resource.
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. 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 Lambda function in Account A must upload reports to an S3 bucket in Account B. Security does not want long-lived access keys anywhere, and the access should be easy to revoke from Account B. Which approach is best?
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
Create an IAM role in Account B that Account A can assume through STS, then grant the role S3 permissions.
Option A is correct because it uses cross-account IAM roles with AWS Security Token Service (STS) to grant temporary credentials to the Lambda function. This avoids long-lived access keys, and the permissions can be revoked immediately by modifying or deleting the role in Account B, meeting the security requirements.
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.
- ✓
Create an IAM role in Account B that Account A can assume through STS, then grant the role S3 permissions.
Why this is correct
Cross-account role assumption with AWS STS is the standard way to grant temporary access without sharing long-lived credentials. By placing the permissions on a role in Account B and controlling the trust policy there, the bucket-owning account keeps central control and can revoke access by changing the trust relationship or permissions. The Lambda execution role in Account A assumes the role when needed and receives short-lived credentials only.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create an IAM user in Account B and store its access keys in Lambda environment variables.
Why it's wrong here
Static access keys are long-lived credentials and create unnecessary operational and security risk.
When this WOULD be correct
This option would be correct if the question stated that the Lambda function must use long-lived credentials (e.g., for legacy system compatibility) and the security requirement to avoid them was absent. It might also be acceptable in a single-account scenario where IAM users are the only option.
- ✗
Attach a security group to the Lambda function that allows outbound traffic to the bucket.
Why it's wrong here
Security groups do not grant S3 permissions, and Lambda does not use security groups as an authorization mechanism for S3 access.
When this WOULD be correct
A question where a Lambda function needs to access an S3 bucket in the same account, and the concern is network-level restriction (e.g., VPC endpoint). Then attaching a security group to the Lambda function (via VPC configuration) to allow outbound traffic to the S3 VPC endpoint would be correct.
- ✗
Use AWS Organizations SCPs to grant the Lambda function permission to write to the bucket.
Why it's wrong here
SCPs can only restrict permissions, not grant access to a specific workload or resource.
When this WOULD be correct
An SCP would be correct if the question asked how to prevent all accounts in an organization from writing to a specific S3 bucket, or to enforce a policy that restricts S3 bucket access across multiple accounts for compliance reasons.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The SAA-C03 exam frequently reuses these exact scenarios with slightly different constraints.
✓Create an IAM role in Account B that Account A can assume through STS, then grant the role S3 permissions.Correct answer▾
Why this is correct
Cross-account role assumption with AWS STS is the standard way to grant temporary access without sharing long-lived credentials. By placing the permissions on a role in Account B and controlling the trust policy there, the bucket-owning account keeps central control and can revoke access by changing the trust relationship or permissions. The Lambda execution role in Account A assumes the role when needed and receives short-lived credentials only.
✗Create an IAM user in Account B and store its access keys in Lambda environment variables.Wrong answer — click to see why▾
Why this is wrong here
Option B uses long-lived access keys stored in Lambda environment variables, violating the security requirement to avoid long-lived credentials. Additionally, revoking access requires deleting or rotating the keys in Account B, which is less straightforward than removing a role trust policy.
★ When this WOULD be the correct answer
This option would be correct if the question stated that the Lambda function must use long-lived credentials (e.g., for legacy system compatibility) and the security requirement to avoid them was absent. It might also be acceptable in a single-account scenario where IAM users are the only option.
Why candidates choose this
Candidates may think storing keys in environment variables is acceptable because it avoids hardcoding, and they may overlook the 'no long-lived access keys' constraint. The simplicity of creating an IAM user and directly using its keys can seem easier than setting up cross-account roles.
✗Attach a security group to the Lambda function that allows outbound traffic to the bucket.Wrong answer — click to see why▾
Why this is wrong here
Security groups control network traffic at the instance level, not S3 bucket access. They cannot grant or deny API-level permissions to write objects; S3 uses IAM policies, bucket policies, or ACLs for authorization.
★ When this WOULD be the correct answer
A question where a Lambda function needs to access an S3 bucket in the same account, and the concern is network-level restriction (e.g., VPC endpoint). Then attaching a security group to the Lambda function (via VPC configuration) to allow outbound traffic to the S3 VPC endpoint would be correct.
Why candidates choose this
Candidates may confuse network access control (security groups) with identity-based access control (IAM), thinking that allowing outbound traffic to the bucket's IP range is sufficient to grant write permissions.
✗Use AWS Organizations SCPs to grant the Lambda function permission to write to the bucket.Wrong answer — click to see why▾
Why this is wrong here
SCPs are used to centrally control permissions for all accounts in an AWS Organization, not to grant cross-account access to a specific Lambda function. They can only deny or allow permissions at the account level, not to individual resources like a Lambda function.
★ When this WOULD be the correct answer
An SCP would be correct if the question asked how to prevent all accounts in an organization from writing to a specific S3 bucket, or to enforce a policy that restricts S3 bucket access across multiple accounts for compliance reasons.
Why candidates choose this
Candidates may confuse SCPs with IAM policies, thinking they can grant fine-grained permissions to individual resources, or they may overestimate the scope of SCPs as a tool for cross-account access.
Analysis generated from the official SAA-C03blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse security groups (network-layer controls) with IAM policies (identity-based access), or mistakenly think SCPs can grant cross-account permissions when they only act as guardrails.
Detailed technical explanation
How to think about this question
When the Lambda function assumes the IAM role in Account B via STS, it receives temporary credentials (access key, secret key, session token) valid for up to 1 hour by default (configurable up to 12 hours). The role's trust policy must explicitly allow the Lambda execution role in Account A to assume it, and the S3 bucket policy in Account B must grant the role's ARN the necessary s3:PutObject permissions. This pattern is commonly used for cross-account data ingestion pipelines where audit trails and revocation are critical.
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.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
What to study next
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
Design Secure Architectures — This question tests Design Secure Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create an IAM role in Account B that Account A can assume through STS, then grant the role S3 permissions. — Option A is correct because it uses cross-account IAM roles with AWS Security Token Service (STS) to grant temporary credentials to the Lambda function. This avoids long-lived access keys, and the permissions can be revoked immediately by modifying or deleting the role in Account B, meeting the security requirements.
What should I do if I get this SAA-C03 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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