To redesign the edge security to help mitigate the DDoS attack risk in the future, the engineer could do the following:

Move the static content to Amazon S3, and front this with an Amazon CloudFront distribution. This allows the engineer to use a global content delivery network that can cache static content at edge locations and reduce the load on the origin servers.

Use AWS WAF security rules to inspect the inbound traffic. This allows the engineer to use web application firewall rules that can filter malicious requests based on IP addresses, headers, body, or URI strings, and block them before they reach the web servers.

Use Amazon Route 53 to distribute traffic. This allows the engineer to use a scalable and highly available DNS service that can route traffic based on different policies, such as latency, geolocation, or health checks.