Softlayer just announced that they've deployed a new IPv4 Anycast based DNS service. This is particularly fun for me, because I've been running a large (200,000+ domains) authoritative DNS service using Anycast out of two datacenters for over three years now. I've also set this up for a few smaller ISPs and web startups in the past two years.
When we built our service, Anycast was a pretty new concept, somewhat considered voodoo and worrisome to uplink providers. Back then the only known instances of it being used outside of labs was the K.Root server, Akamai, and UltraDNS (now Neustar). outside of the K.Root server were Akamai, UltraDNS, and some of the then up and comers in the Content Delivery Network industry. Now it's starting to become rather common-place.
Anycast is actually a pretty simple design to apply to stateless network protocols to achieve high levels of fault tolerance and low latency. We've been able to maintain 99.9999% uptime on our DNS infrastructure. At it's core you're advertising the same Autonomous Systems Numbers and their respective ip blocks out of two physical locations. On the public internet, this is achieved through BGP, but will work with any vector based routing protocol like OSPF.
Consider this a poor man's route optimizer. BGP is going to "do the right thing" by connecting you to through the datacenter which is advertising this ip block via the lower number of BGP hops. The more physical locations you replicate your service, and advertise your IP block out of, the fewer hops end-users have to traverse to reach your service. Of course, with over 266,000 entries in the core routing table, the shortest path from point A to point B can change from one minute to the next, making Anycast a bad idea for anything stateful (TCP), and increasing the requirements for your inter-datacenter replication to be solid.
Anycast isn't necessarily a closed door for stateful network services. One common use of Anycast now is to build a poor man's CDN (yes, lots of poor men are building network services today). The design here is the same as an Anycast DNS service, but you have file transfer servers in each datacenter as well. The DNS servers in each location keep their TTLS very low (usually 60 seconds) and return IP addresses for it's respective local file servers.
A few good Anycast references:
Softlayer's press release is at http://www.softlayer.com/press_2008_08_25.html
SoftLayer Adds Geographically Redundant DNS to Its Set of Enterprise Class Features
August 25, 2008, Dallas, TX – SoftLayer now offers Anycast DNS (also called IP Anycast Routing) free to all customers using SoftLayer’s DNS servers. Anycast DNS is a high availability and geographically diverse advanced routing solution that allows multiple server destinations to share the same IP address and routes IP requests to the best destination based on network conditions. This enterprise-class feature increases uptime, provides exceptional opportunities for optimizing traffic flow, improves network performance, and maintains service redundancies. Previously, this functionality has not been available to organizations of all sizes as it is difficult to build in-house and very expensive to purchase from third party providers.
“We are very excited to offer a high availability DNS solution to the market. Its capabilities give our customers another level of reliability and an effective mechanism for maintaining business continuity,” said Jacob Linscott, SoftLayer’s Director of Information Systems.
Anycast DNS routing is available from all three SoftLayer data centers. All of SoftLayer’s resilient name servers have the feature enabled and offer real-time DNS record population.
How it works:
By allowing multiple destinations to share the same IP address, Anycast DNS routing permits DNS registration information to be mirrored on server clusters either locally, regionally, or globally. Requests for the IP address are routed to the closest destination with the highest availability, preventing requests from being routed to a server that is unavailable or experiencing unusually heavy traffic.
Key advantages include:
Service Continuity—helps maintain uptime in the event of service interruptions
Network Protection—provides a comprehensive network failover solution
Disaster Recovery—allows critical services to be continuously maintained
About SoftLayer Technologies
Headquartered in Plano, Texas, SoftLayer delivers next generation webhosting and on-demand datacenter services located in Dallas TX and Seattle WA. Utilizing proprietary software, coupled with the industry's first network-within-a-network topology, the company delivers unprecedented power and control to securely manage IT environments while providing unparalleled scalability. For more information please visit www.softlayer.com or call 866.398.7638.
Michael Halligan is a serial entrepreneur with more than 15 years of experience in IT architecture and operations. His primary role is chief technical officer of BitPusher, LLC, a managed application hosting firm based out of San Francisco and Seattle. He is currently starting up a new Web application providing intelligent services to the convention industry. He previously held architectural and management positions at start-ups MyPoints, Kontiki and Napster.