AWS Certified Solutions Architect – Professional — Question 979

A medical company is running a REST API on a set of Amazon EC2 instances. The EC2 instances run in an Auto Scaling group behind an Application Load
Balancer (ALB). The ALB runs in three public subnets, and the EC2 instances run in three private subnets. The company has deployed an Amazon CloudFront distribution that has the ALB as the only origin.
Which solution should a solutions architect recommend to enhance the origin security?

Answer options

• A. Store a random string in AWS Secrets Manager. Create an AWS Lambda function for automatic secret rotation. Configure CloudFront to inject the random string as a custom HTTP header for the origin request. Create an AWS WAF web ACL rule with a string match rule for the custom header. Associate the web ACL with the ALB.
• B. Create an AWS WAF web ACL rule with an IP match condition of the CloudFront service IP address ranges. Associate the web ACL with the ALB. Move the ALB into the three private subnets.
• C. Store a random string in AWS Systems Manager Parameter Store. Configure Parameter Store automatic rotation for the string. Configure CloudFront to inject the random string as a custom HTTP header for the origin request. Inspect the value of the custom HTTP header, and block access in the ALB.
• D. Configure AWS Shield Advanced. Create a security group policy to allow connections from CloudFront service IP address ranges. Add the policy to AWS Shield Advanced, and attach the policy to the ALB.

Correct answer: A

Explanation

Option A is correct because using a custom HTTP header injected by CloudFront and verified by AWS WAF on the ALB ensures that only requests originating from the CloudFront distribution are permitted, with AWS Secrets Manager and Lambda handling the secure rotation of the secret key. Option B is incorrect because an ALB facing CloudFront must remain in public subnets to receive traffic. Option C is incorrect because Systems Manager Parameter Store does not support automatic rotation natively, and AWS WAF is required to properly inspect and block requests based on custom headers at the ALB.