[skuhn]

Once you have configured your zone with multiple providers, it's simply a matter of adding NS entries for each provider's authoritative servers to your registrar. The harder part is ensuring that the zones are kept in sync and that you don't rely on features (such as GSLB stuff or ALIAS records) that aren't available with all providers.

It's up to the client resolver to handle failover, so it's not perfect in terms of availability, but better than nothing.

For example:

  $ dig ns amazon.com
  amazon.com.		3599	IN	NS	ns4.p31.dynect.net.
  amazon.com.		3599	IN	NS	ns1.p31.dynect.net.
  amazon.com.		3599	IN	NS	ns3.p31.dynect.net.
  amazon.com.		3599	IN	NS	ns2.p31.dynect.net.
  amazon.com.		3599	IN	NS	pdns1.ultradns.net.
  amazon.com.		3599	IN	NS	pdns6.ultradns.co.uk.

(note that this is also TLD redundant, since there's a .co.uk included)

[captncraig]

The tricky part is making sure the apex NS records are consistent across all authoritative nameservers. A surprising number of dns providers do not let you edit those.

[skuhn]

Yeah, it does need to be the same in the zone as well as with your registrar. As mentioned in StackOverflow's blog post, Azure doesn't support changing NS records.

Similarly, there are a fair number of DNS providers that don't allow you to use all DNS record types. For something so simple, providers can really go out of their way to screw it up.