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Comment by anderspetersson | Hacker News Reader

How do you do this on the DNS layer? Very short TTL and switching on failure detection? Do you use both providers at the same time when both are up via DNS round robin or similar?

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There's nothing stopping you from adding multiple A records for a domain. In fact, that's what a lot of people do:

  dig a www.google.com

  www.google.com.         300     IN      A       74.125.237.178
  www.google.com.         300     IN      A       74.125.237.177
  www.google.com.         300     IN      A       74.125.237.176
  www.google.com.         300     IN      A       74.125.237.179
  www.google.com.         300     IN      A       74.125.237.180

Browsers these days will resolve and try each one, on a first-come-first-served basis. If one fails, it will try the request on the next server.

If you have your own IP-space you can use BGP to route IPs to different locations.

If you're relying on DNS then short TTLs are pretty reliable, but there can be extended outages due to erroneous client-caching.

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