[quintin]

https://serverfault.com/questions/145777/what-s-the-point-in...

" One of the reasons why you need www or some other subdomain has to do with a quirk of DNS and the CNAME record.

Suppose for the purposes of this example that you are running a big site and contract out hosting to a CDN (Content Distribution Network) such as Akamai. What you typically do is set up the DNS record for your site as a CNAME to some akamai.com address. This gives the CDN the opportunity to supply an IP address that is close to the browser (in geographic or network terms). If you used an A record on your site, then you would not be able to offer this flexibility.

The quirk of the DNS is that if you have a CNAME record for a host name, you cannot have any other records for that same host. However, your top level domain example.com usually must have an NS and SOA record. Therefore, you cannot also add a CNAME record for example.com.

The use of www.example.com gives you the opportunity to use a CNAME for www that points to your CDN, while leaving the required NS and SOA records on example.com. The example.com record will usually also have an A record to point to a host that will redirect to www.example.com using an HTTP redirect."

[cortesoft]

A lot of DNS providers these days will give you a pseudo-cname on apex... basically having the dns resolver do a lookup of another dns name and return that as an A record for the apex.

[guitarbill]

CloudFlare calls this CNAME flattening, right? [0][1] Personally, I always enjoy engineering solution that mean we're not stuck with old decisions forever. I chose the non-www as a teenager, and I'm glad 10+ years later I could add email to my domain no problem.

[0] https://blog.cloudflare.com/introducing-cname-flattening-rfc...

[1] similar discussion, 2014: https://news.ycombinator.com/item?id=7293512

[paulddraper]

Yes. AWS Route 53 can do this for root or non-root records. They call these "ALIAS" records.

[snuxoll]

> The quirk of the DNS is that if you have a CNAME record for a host name, you cannot have any other records for that same host. However, your top level domain example.com usually must have an NS and SOA record. Therefore, you cannot also add a CNAME record for example.com.

I discovered this when using a CNAME for a root-level domain and then wondering why I had spotty mail delivery. Turns out, quite a few mail systems and/or DNS resolvers handle this fine - but there are still quite a lot that don't.

[greenleafjacob]

Wouldn't anycast be a solution? Then the CDN can provide the same IP to all users, but the network layer ensures that the IP is one close to the user.

[Ayesh]

Expensive, but yes, anycast solves it.

[lotyrin]

Yep.

Source: had to navigate the shitty position of trying to CNAME to a CDN and have that CDN's DNS infra replicate our e.g. MX records.