Today it is not common to publish a website on the root domain (also named “domain apex”), while running the site via CDN (content delivery network) is the recent trend that can give end-users excellent experience. CDN provides you with an endpoint to the point in DNS, and sometimes you can’t use a CNAME on the root domain. What to do?
Good news: DNS providers have a solution called ANAME, or ALIAS: it allows pointing to the CDN endpoint on the root domain. Many companies feature this solution. ANAME/ALIAS is resolved instead of a recursive resolver (ISP, Public DNS, OpenDNS, etc.), which is why end-users may be routed not to the closest CDN PoP and get poor experience.
There are three solutions for this problem:
- 1. DNS providers should do better job. The authoritative DNS should act smarter when resolving ANAME from nameservers. There’s a EDNS-Client-Subnet approach: a part of the IP address of the original query source is sent to the CDN’s DNS server. If DNS provider received a query from OpenDNS or Public DNS, client IP address subnet should be passed along. If query comes from an ISP resolver, the authority server sends subnet of resolver’s IP to the query to CDN’s DNS server.
- 2. Use integrated authoritative DNS and CDN. Many global CDN providers provide authoritative DNS services. Their DNS and CDN work together, so the authoritative DNS always knows what the best CDN IPs are, no matter what query comes in.
- 3. Deploy an Anycast CDN. Edgecast, Highwinds, and many other providers have CDNs that use Anycast to route users to the best PoP. All PoPs have the same IP address, which eliminates the problem of the root domain, and users are automatically directed to the closest PoP with the shortest network path.
Note that some CDN providers use Anycast for specific regions, or for a limited number of users.