The company put a public Network Load Balancer in front of its application. The application instances do not use Elastic IP addresses. Users should reach the app using the corporate domain name. What is the most cost-effective Route 53 configuration to route traffic to the NLB?

The most cost-effective solution is to create a Route 53 alias record pointing to the NLB. Alias records are a Route 53-specific extension that allows you to map your domain name to AWS resources like Load Balancers, CloudFront distributions, or S3 buckets, and are free of charge for queries. They also automatically track IP address changes of the underlying AWS resource. AAAA records are for IPv6 addresses and are not ideal for an NLB, which can have dynamic IPs. CAA records are for Certificate Authority Authorization and are unrelated to traffic routing. CNAME records would work but incur standard Route 53 query charges, making them less cost-effective than alias records for AWS resources.