I remember reading about the no-www movement years ago. At that time it struck me as a cool thing to do, but I now know that no-www is a really bad idea in general. That’s because the DNS system lets you assign CNAME records to subdomains, including the www subdomain, but only A or AAAA records to root domains. In other words, you can say that www.example.com is the same as test.example.org, but you can only say that example.com is the same as a particular IP address.

What’s the benefit of this? Well, if you use a CNAME you can let the owner of test.example.org deal with anycast and routing issues, but if you use A records you have to deal with them yourself. If you do decide to deal with them yourself, you’ll be frustrated when your DNS updates take a while to propagate.

More generally, CNAME is an example of the most powerful law of computer science in action, and A isn’t.

All problems in computer science can be solved by another level of indirection. David Wheeler

See Heroku’s documentation on the matter.