First off let’s start with CNAME, this maps a hostname to another hostname. CNAME does not work on the root domain so website.com won’t work but app.website.com will work. So for example you could set app.website.com to map to the DNS name of your load balancer that links to your EC2 hosts running your website or even link it directly to an EC2 host, this service is paid as well. Next up we have the ALIAS, this maps hostnames to an AWS resource such as an ALB. It is a free service, offers health monitoring that can be enabled, is either an A or AAAA record, and works on the root level so you could use website.com. ALIAS definitely has several advantages but as I mentioned it only works with AWS resources and those don’t include EC2 instance names you’ll have to use a CNAME for those. I should note as well you are unable to set a TTL on an ALIAS it is set by Route 53 automatically. If possible I recommend using an ALIAS due to its wider functionality. CNAME does have its uses, especially if you don’t leverage a lot of AWS resources.