Load Balancing & Auto Scaling

A CNAME points a name to another name with an extra lookup and cannot sit at the root domain, while a Route 53 alias points straight to the AWS resource's IPs at the root domain, for free, and tracks its changing addresses automatically.

ALB reads the request and routes by content at Layer 7, NLB just forwards packets blazingly fast at Layer 4, and GWLB inserts security appliances in the path.