Which solution meets these requirements and is MOST secure?

Explanations:

While using a public ALB and CloudFront for content delivery, placing the EC2 instances in public subnets exposes them directly to the internet, increasing security risks. Additionally, CloudFront should ideally use a private ALB as the origin to enhance security by not exposing the backend directly to the public.

This configuration suggests using a public ALB with EC2 instances in private subnets and CloudFront as the content delivery network (CDN). However, without a public-facing ALB, CloudFront cannot access the EC2 instances, making this option impractical for serving content.

This option offers a secure design with a public ALB directing traffic to multiple redundant EC2 instances in private subnets. CloudFront, serving HTTPS content, acts as a secure front that reduces latency by caching content at the edge, while keeping the application tier secure from direct internet exposure.

This configuration uses a public ALB and places EC2 instances in public subnets, which exposes the backend directly to the internet. While CloudFront can deliver content, this approach lacks the necessary security, as it does not utilize private subnets for the application tier.