Hey, this brings up a good point for some more clarification.
There are two common ways CDNs do routing:
method 1) by using a customized dns server (like the one I used in the example) that responds differently to the resolvers end users use. You can use something like Maxmind (like I did in the example) to determine where you think that resolver is.
method 2) you can use anycast all the way to the TCP level for terminating traffic to ports 80 and 443. This is the most common way we do it at MaxCDN.com. We find it to be the fastest.
To do method 1 you can use the Go GeoDNS server from github (and there's one in PERL) or you can use a service like Dyn.com, DNSMadeEasy (only has broad geo), NSone.net, Verisign's DNS product or Cedexis (which can also incorporate latency data). One thing to keep in mind with doing DNS based routing is eDns for the big public DNS providers. The downside is that you can only respond by the resolver or edns subnet someone uses which can lead to a lot of inaccuracies. The big pro about method 1 is it's easy to deploy and it's easy to balance traffic if a PoP gets over loaded since it's just DNS records.
Anycast (Method 2) is great and fast, but it is high maintenance. We've spent a lot of time tweaking this over the past 4 years at MaxCDN. I've heard you can announce anycast blocks with ServerCenteral and Internap, but I haven't tried it. I've done it with Softlayer for testing. You need to have your own /24 to do it with them. We have our own infrastructure and several upstream providers. The biggest challenges with anycast are dealing with Asia (to make sure routes don't trombone) and traffic management since you can't control where traffic goes.
There are two common ways CDNs do routing:
method 1) by using a customized dns server (like the one I used in the example) that responds differently to the resolvers end users use. You can use something like Maxmind (like I did in the example) to determine where you think that resolver is.
method 2) you can use anycast all the way to the TCP level for terminating traffic to ports 80 and 443. This is the most common way we do it at MaxCDN.com. We find it to be the fastest.
To do method 1 you can use the Go GeoDNS server from github (and there's one in PERL) or you can use a service like Dyn.com, DNSMadeEasy (only has broad geo), NSone.net, Verisign's DNS product or Cedexis (which can also incorporate latency data). One thing to keep in mind with doing DNS based routing is eDns for the big public DNS providers. The downside is that you can only respond by the resolver or edns subnet someone uses which can lead to a lot of inaccuracies. The big pro about method 1 is it's easy to deploy and it's easy to balance traffic if a PoP gets over loaded since it's just DNS records.
Anycast (Method 2) is great and fast, but it is high maintenance. We've spent a lot of time tweaking this over the past 4 years at MaxCDN. I've heard you can announce anycast blocks with ServerCenteral and Internap, but I haven't tried it. I've done it with Softlayer for testing. You need to have your own /24 to do it with them. We have our own infrastructure and several upstream providers. The biggest challenges with anycast are dealing with Asia (to make sure routes don't trombone) and traffic management since you can't control where traffic goes.
One of our guys did a blog post on this a while ago: http://blog.maxcdn.com/anycast-ip-routing-used-maxcdn/
Hope this is useful for some!