A company is running a containerized application on an Amazon Elastic Container Service (Amazon ECS)...

The correct solution is option D because it effectively prevents direct access to the internet-facing ALB while allowing legitimate traffic that originates from Amazon CloudFront. By configuring CloudFront to include a custom HTTP header (such as X-Shared-Secret) in all origin requests, and then configuring ALB listener rules to only forward requests that contain the expected header value, the ALB will reject any requests that bypass CloudFront.

This approach is a documented AWS best practice when CloudFront is placed in front of an ALB and AWS WAF is associated with the CloudFront distribution. AWS WAF only evaluates traffic that flows through CloudFront; therefore, preventing direct access to the ALB is critical to ensure that all requests are inspected by the web ACL.

Option A is invalid because CloudFront does not support AWS PrivateLink endpoints as origins. Option B is incorrect because CloudFront cannot use an internal ALB as an origin; CloudFront requires a publicly reachable origin. Option C is not recommended because CloudFront IP ranges change frequently, making IP-based allow lists operationally complex and error-prone, and AWS does not provide a supported CloudFront prefix list for ALB listener rules.

AWS Security Specialty guidance explicitly recommends using custom origin headers to restrict ALB access to CloudFront-only traffic, making option D the correct and secure solution.