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I'm building a global CDN and have a DNS service that will direct customers to the closest server. However I need rapid failover if one of the data centers e.g. Germany goes down users need to be instantly served from London.

The DNS service I'm looking at provides DNS failover but it requires a low TTL which increases queries and is therefore costly - and some ISP's don't respect TTL, so you're still going to best case have a delay of 300 seconds before switchover and worst case up to 48 hours as a bad ISP caches a DNS entry in their servers.

Any ideas on how to provide rapid failover from one data center to another at a reasonable price?

Mark172
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1 Answers1

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The technology you are looking for is called Anycast. http://en.wikipedia.org/wiki/Anycast

Anycast is a network addressing and routing methodology in which datagrams from a single sender are routed to the topologically nearest node in a group of potential receivers, though it may be sent to several nodes, all identified by the same destination address.

I would also suggest you read on BGP.

CloudWeavers
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  • You took the words out of my mouth – Mark Henderson Sep 16 '14 at 22:53
  • A little mroe color: anycast is most often associated with stateless UDP protocols like DNS. But most of the "newer" CDNs utilize anycast not just for their DNS, but also for the actual TCP connections made by clients as well. See CloudFlare, MaxCDN, CacheFly, etc. Akamai, Limelight, and Amazon CloudFront still seem to utilize per-DC IP addressing for client (usually web browser) connections, which means they too are dependent on DNS timeouts for failover (or perhaps they have some fast-rerouting/tunneling tricks with their upstream providers to move IP blocks from failed DCs to a working one) – rmalayter Mar 07 '15 at 15:47