AWS Certified Solutions Architect – Professional — Question 461

You have an application running on an EC2 instance which will allow users to download files from a private S3 bucket using a pre-signed URL. Before generating the URL, the application should verify the existence of the file in S3.
How should the application use AWS credentials to access the S3 bucket securely?

Answer options

• A. Use the AWS account access keys; the application retrieves the credentials from the source code of the application.
• B. Create an IAM role for EC2 that allows list access to objects in the S3 bucket; launch the Instance with the role, and retrieve the role's credentials from the EC2 instance metadata.
• C. Create an IAM user for the application with permissions that allow list access to the S3 bucket; the application retrieves the IAM user credentials from a temporary directory with permissions that allow read access only to the Application user.
• D. Create an IAM user for the application with permissions that allow list access to the S3 bucket; launch the instance as the IAM user, and retrieve the IAM user's credentials from the EC2 instance user data.

Correct answer: B

Explanation

Using an IAM role for EC2 is the AWS-recommended best practice for securely granting applications on EC2 instances access to other AWS services like S3. This method avoids hardcoding or storing long-term credentials on the instance, as the AWS SDK automatically retrieves temporary security credentials from the EC2 instance metadata. Storing access keys in source code, local directories, or user data (Options A, C, and D) exposes credentials and violates security best practices.