On Wed, Feb 1, 2012 at 3:25 PM, Anurag Bhatia <me@anuragbhatia.com> wrote:
Hello everyone!
I have a small question and was wondering if someone could help me with that.
Question is - why companies like Google, Amazon are having partial anycasting in CDN setups? E.g if we pick a random hostname from url of Picasa picture - lh3.googleusercontent.com - this one is further a cname string and at the end you will find different A records when checked from different locations.
The simple answer for this is, Google cannot be expected to have a local cache of every image supplied to them globally on every server. So they use unicast servers behind a DNS based geo load balancer configuration. As for DNS, every anycasted node is expected to be able to resolve any DNS request that is made. It's all a matter of disk and acceptable delay in providing the data from the "closest" disk. charles