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We're looking at lowering our DNS A record TTL to around 1 minute, to enable us to quickly switch to a backup server should the main one fail (whether this is automatic, using AWS Health Checks etc, or manual, is largely irrelevant to this question).

I'm aware this will put a significantly higher load on the DNS server, but this isn't an issue.

What I'm concerned about it how the total site load time will be increased, because of the additional overhead of having to look up the DNS records with a lot more requests.

How to I balance these issues?

I'm obviously disregarding factors outside my control, such as ISP DNS caching.

  • Many recursive DNS providers will not honour a TTL of 1 minute or less. Safe bet is probably nothing less than 5 minutes. – Patrick Mevzek Sep 11 at 18:32
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You should instead have some kind of proxy (or load-balancer) in place which would route all the traffic to backup server when main server is down without requiring to do any DNS changes.

The implementation on this depends a lot on what you are trying to accomplish though, but the information in the question that you have provided is more general.

  • A load balancer is overkill, as we're not expecting a huge amount of traffic, but do need 100% uptime (or as close to that as possible). – user37315 Mar 27 '14 at 9:20
  • A load balancer can be found in firewalls as affordable as Netgear and Cisco ranging from $220 - $400 the last I looked. – closetnoc Mar 27 '14 at 15:20
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    I will let you in on a secret. New and unpublished security methods exist in a race to secure the infrastructure of U.S. networks and systems. One major metric that stands alone as a trigger is very short TTL times. This may be enough of a trigger to block systems from whole networks and add domain names and IP addresses to black-lists. Short TTL times indicate deliberate attacks and used as a method to obfuscate hacker identities and the allow the attack rapid mobility to avoid blocking. – closetnoc Mar 27 '14 at 15:43

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