The Inflexibility of DNS Traditionally, the root record of a domain needed to point to an IP address (known as an A -- for "address" -- Record). While it may not seem like a big deal, tying a service to an IP address can be extremely limiting. Imagine that a new blogging platform, WordPlumblr, starts up. WordPlumblr allows its users to use custom domains that point to the WordPlumblr infrastructure. Foo.com signs up and WordPlumblr gives Foo.com an IP address. The supply of IP addresses is limited so, over time, as more sites sign up, IP addresses end up getting shared between multiple customers. No problem since with virtual hostnames WordPlumblr can return different content for different domains even hosted on the same IP address.

Everything is fine until Foo.com starts using too many of WordPlumblr's resources -- maybe because they're being attacked or they're featured on Oprah or who knows why. The other customers of WordPlumblr get poor performance because they're sharing the same resources as the overwhelmed Foo.com. WordPlumblr is put in a difficult position: having to reach out to Foo.com to get them to change their DNS settings or, even harder, having to reach out to all the other customers using the IP address to get them to change. Good luck.

CNAMEs For the Win The solution is a CNAME. A CNAME is an alias. It allows one domain to point to another domain which, eventually if you follow the CNAME chain, will resolve to an A record and IP address. If WordPlumblr had handed out a unique CNAME for every customer then they wouldn't have had a problem. For example, WordPlumblr might have assigned the CNAME 6equj5.wordplumblr.com for Foo.com. Foo.com and the other customers may have all initially resolved, at the end of the CNAME chain, to the same IP address. However, when Foo.com started using too many resources WordPlumblr could have updated the CNAME and isolated Foo.com from the rest of the customers.

If you're familiar with programming, this is just like the idea of a pointer. When you're programming in C, in order to allow flexibility in memory management, you usually don't want to address memory directly but, instead, you set up a pointer to a block of memory where you're going to store something. If the operating system needs to move the memory around then it just updates the pointer to point to wherever the chunk of memory has been moved to. The program references the pointer and is none the wiser.

CNAMEs work great for subdomains like foo.com or blog.foo.com. Unfortunately, they don't work for a naked domain like foo.com itself. And, for reasons that somewhat perplex me, a lot of people are obsessed with using their naked domain for their website. So why don't CNAMEs work at the root?