The Windows Azure Domain Name System (DNS) is moving to a new globally distributed infrastructure, which will increase performance and improve reliability of DNS resolution. In particular, users who access Windows Azure applications from outside the United States will see a decrease in the time it takes to resolve the applications' DNS names. This change will take effect on October 5th, at midnight UTC. Customers don't need to do anything to get these improvements, and there will be no service interruption during the changeover.
Because of the inherently distributed nature of this new global infrastructure, the creation of new DNS names associated with a Windows Azure application can take up to two minutes to be fully addressable on a global basis. During this propagation time, new DNS records will resolve as NXDOMAIN. If you attempt to access the new DNS name during this time window, most client computers will cache these negative responses for up to 15 minutes, causing "DNS Not Found" messages. Under most circumstances you will not notice this delay, but if you promote a Windows Azure staging deployment to production for a brand new hosted service, you may observe a delay in availability of DNS resolution.