

Protecting your site against DNS outages - sedds
http://blog.women.com/protecting-your-site-against-dns-outages/

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rdl
This works for simple DNS configurations, but gets a lot more complicated if
you use DNS based load balancing, any kind of automated changes to DNS,
DNSSEC, etc.

Also, I would absolutely make sure you have a way to keep records in sync.
Updating the backup should be an automatic part of updating any records.

