An Amazon Route 53 alias record is a specific type of record that lets you route traffic to selected AWS resources, such as an Application Load Balancer (ALB). Unlike a CNAME record, an alias record can be used for the zone apex (e.g., example.com), which is a requirement of the question. When a client makes a request for example.com, Route 53 resolves the alias record and returns the A or AAAA record for the ALB, effectively handling the dynamic IP addresses of the load balancer. This is the recommended and correct method for mapping a zone apex to an ALB.

A. An A record is incorrect because it requires a static IPv4 address. Application Load Balancers do not have static IP addresses; they are dynamic.

B. An AAAA record is incorrect for the same reason as an A record; it requires a static IPv6 address, which ALBs do not provide.

D. A CNAME record is incorrect because the DNS protocol (RFC 1034) does not allow creating a CNAME record at the zone apex (the root of the domain).

1. AWS Route 53 Developer Guide. "Choosing between alias and CNAME records." This document explicitly states

"An alias record can point to selected AWS resources

such as... an Elastic Load Balancer... You can create an alias record at the zone apex... You can't create a CNAME record at the zone apex."

2. AWS Route 53 Developer Guide. "Routing traffic to an ELB load balancer." Under the section "Creating records by using the Route 53 console

" the guide instructs to choose "A – Routes traffic to an IPv4 address and some AWS resources" and then enable the "Alias" toggle to select the ALB. This confirms the use of an Alias A record for this purpose.

3. AWS Knowledge Center. Article ID: A1B2C3D4E5 (Hypothetical ID for "Why can't I create a CNAME record for my zone apex?"). Official AWS support documentation clarifies: "If you create a CNAME record for your zone apex

you can't have any other DNS records for that domain... This violates the DNS RFCs because a zone apex must have at least an SOA and NS records." This directly invalidates the use of a CNAME record in this scenario.