Least Privilege S3 Access for AWS Lambda
Short answer
C Create individual IAM roles for each Lambda function and assign them as execution roles to ensure least privilege access to the S3 bucket.
Question
Key Takeaways
The core concept is identity-based security; the common trap is choosing bucket policies over IAM roles, which are less granular and harder to manage for individual functions.
This question tests the design of secure access to AWS resources using IAM roles and least privilege principles. The correct solution involves assigning unique execution roles to each Lambda function.
Common mistake: Many learners select Option D (Bucket Policy), believing it directly restricts access by ARN. However, while technically possible, Option C is the standard best practice for managing permissions at the service level with greater flexibility and scalability.
Expert Analysis
Why the Answer Is Correct
Option C is the correct answer because it implements the principle of least privilege by creating distinct IAM roles for each Lambda function. Each role grants only the specific permissions required for that function to access the S3 bucket, minimizing the risk if one function is compromised. This approach aligns with AWS best practices for securing compute services.
Why the Other Options Are Wrong
Option A violates least privilege by granting full bucket access to all functions via a shared role. Option B relies on VPC endpoint IPs, which can be complex to manage and less precise than IAM permissions. Option D uses a bucket policy based on ARNs; while valid, it is generally considered less scalable and flexible than using IAM roles for fine-grained control over multiple distinct functions.
Community Comment Notes
Community consensus strongly supports Option C as the most robust architectural choice. Some users debated Option D, noting that while it works, it lacks the flexibility of IAM roles. One commenter highlighted that IP-based policies (Option B) are harder to manage and less secure than IAM roles. The general agreement is that separate roles provide the narrowest scope of access.
Exam Strategy
Always prioritize IAM roles over bucket policies when dealing with multiple AWS services communicating securely, as roles offer better granularity and ease of management.
Frequently Asked Questions
Why is Option D not the best answer?
Can I use a single IAM role for all Lambda functions?
Community Votes
100% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 3 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 3
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56ce46c 👍 2i think D is also right S3 Bucket Policy: Use an S3 bucket policy that grants access to the specific Lambda functions based on their function ARNs. This ensures that only the authorized Lambda functions can retrieve data from the S3 bucket.
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swati1508 👍 2A, B and D wrong only C is right
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LeonSauveterre 👍 1 Answered CA - Full access? No! B - Theoretically possible but IP-based policies are harder to manage and not as secure as IAM roles. C - By creating separate IAM roles for each Lambda function, permissions can be narrowly scoped to each function's specific needs. D - This would actually work. It's just that bucket policies based on function ARNs are less flexible and scalable compared to IAM roles, especially when you need to manage permissions for multiple Lambda functions or add new functions.
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