A company manages example.com in Route 53 and placed a CloudFront distribution in front of its web app. The site should be reachable at www.example.com and must use CloudFront. What is the most cost-effective way to configure Route 53 so www.example.com resolves through the CloudFront distribution?

An ALIAS record is the most cost-effective solution because it allows you to map a domain name (like www.example.com) to an AWS resource (like a CloudFront distribution) without incurring Route 53 query charges. ALIAS records are a Route 53-specific extension to DNS. They behave like CNAMEs but can be used at the zone apex (e.g., example.com) and are free for queries. A CNAME record would also work to point www.example.com to the CloudFront distribution's domain name, but it incurs standard DNS query charges, making it less cost-effective than an ALIAS record. An A record points a domain to an IP address, which would bypass CloudFront and expose the origin directly. A PTR record is used for reverse DNS lookups, mapping an IP address back to a hostname, and is irrelevant for this forward-resolution scenario.