AWS Certified Security – Specialty (SCS-C02) — Question 33

A company's public Application Load Balancer (ALB) recently experienced a DDoS attack. To mitigate this issue, the company deployed Amazon CloudFront in front of the ALB so that users would not directly access the Amazon EC2 instances behind the ALB.
The company discovers that some traffic is still coming directly into the ALB and is still being handled by the EC2 instances.
Which combination of steps should the company take to ensure that the EC2 instances will receive traffic only from CloudFront? (Choose two.)

Answer options

• A. Configure CloudFront to add a cache key policy to allow a custom HTTP header that CloudFront sends to the ALB.
• B. Configure CloudFront to add a custom HTTP header to requests that CloudFront sends to the ALB.
• C. Configure the ALB to forward only requests that contain the custom HTTP header.
• D. Configure the ALB and CloudFront to use the X-Forwarded-For header to check client IP addresses.
• E. Configure the ALB and CloudFront to use the same X.509 certificate that is generated by AWS Certificate Manager (ACM).

Correct answer: B, C

Explanation

The correct actions are B and C. By configuring CloudFront to add a custom HTTP header, the ALB can then be set to only process requests that include this header, effectively preventing direct access to the EC2 instances. Options A, D, and E do not directly restrict access to the ALB from non-CloudFront traffic, making them ineffective for this purpose.