The correct answer is that an IAM permissions policy must be attached to the role to grant S3 access. While the trust policy correctly allows the Lambda service to assume the execution role, it only establishes the trust relationship—it does not grant any actions on resources. Without a separate identity-based policy attached to the role that includes specific S3 permissions like s3:GetObject or s3:PutObject, the Lambda function will be denied access to the bucket, even after successfully assuming the role. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of the separation between trust policies (who can assume the role) and permissions policies (what actions the role can perform). A common trap is confusing the trust policy with actual resource permissions; remember that trust is about identity, not authorization. Memory tip: Trust lets you in the door, but a permissions policy gives you the keys to the cabinet.
SAP-C02 Practice Question: Design Solutions for Organizational Complexity
This SAP-C02 practice question tests your understanding of design solutions for organizational complexity. 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.
Refer to the exhibit. A solutions architect is reviewing an IAM trust policy for a Lambda function's execution role. The function needs to access an S3 bucket in the same account. The trust policy is as shown. What is missing for the Lambda function to successfully assume the role?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
An IAM policy must be attached to the role granting permissions to the S3 bucket
Option A is correct because the IAM trust policy only allows the Lambda service to assume the role, but it does not grant any permissions to access the S3 bucket. For the Lambda function to successfully read or write objects in the S3 bucket, an IAM permissions policy (e.g., s3:GetObject, s3:PutObject) must be attached to the role. Without this policy, the role has no effective permissions to perform actions on the bucket, even though the trust policy allows the role to be assumed.
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.
✓
An IAM policy must be attached to the role granting permissions to the S3 bucket
Why this is correct
The trust policy allows Lambda to assume the role, but the role itself needs an IAM policy to grant S3 access.
Related concept
Read the scenario before looking for a memorised answer.
✗
A service control policy must allow Lambda to assume roles
Why it's wrong here
SCPs are not required for service access.
✗
The S3 bucket must have a resource-based policy allowing the Lambda function
Why it's wrong here
Not necessary if the role has permissions via IAM policy.
✗
The trust policy must specify the Lambda function name
Why it's wrong here
The trust policy uses service principal, which is correct.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the trust policy (which controls who can assume the role) with the permissions policy (which controls what actions the role can perform), leading them to think the trust policy alone is sufficient for accessing resources.
Detailed technical explanation
How to think about this question
Under the hood, IAM role assumption involves two distinct policies: the trust policy (which defines who can assume the role) and the permissions policy (which defines what actions the assumed role can perform). When a Lambda function invokes, the AWS Lambda service uses the function's execution role to obtain temporary credentials via the STS AssumeRole API; if the trust policy allows lambda.amazonaws.com, the role is assumed, but subsequent API calls to S3 are evaluated against the permissions policy attached to the role. A common real-world scenario is when a developer attaches only a trust policy and wonders why the function gets 'Access Denied' errors—this is because the permissions policy is missing.
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: An IAM policy must be attached to the role granting permissions to the S3 bucket — Option A is correct because the IAM trust policy only allows the Lambda service to assume the role, but it does not grant any permissions to access the S3 bucket. For the Lambda function to successfully read or write objects in the S3 bucket, an IAM permissions policy (e.g., s3:GetObject, s3:PutObject) must be attached to the role. Without this policy, the role has no effective permissions to perform actions on the bucket, even though the trust policy allows the role to be assumed.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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