Using a low TTL to enable a fail-over cluster?

[phn at icke-reklam.ipsec.nu]

Jakob Bak <Jakob at bak.com> wrote:
> Hi,
> Can anybody help me with your experiences on the following  which I can't
> seem to find any information on:
> 1) How many (%) ISP nameservers on the net respect a TTL of only 5 minutes
> when caching our DNS records?
>     (or do they often keep the information over longer periods e.g 1 hour to
> avoid load)

Any standard conforming nameserver would use the original TTL  

> 2) How much traffic does a secondary DNS get when the primary seem to be
> running perfectly?
>    (0% or ?%)

2 servers would get 50% each, 3 servers 33% etc. There is no
distinction between "primary" or "secondary" they are all
"nameservers" and they are all consulted in "unpredictable order"


> Background:
> our system must now provide 99,99% uptime on our web site so we are
> considering a DNS solution which might enable us to achieve this.
> Essentially, we have been suggested to set up
> - a primary DNS at the same location as our main cluster pointing our domain
> at this cluster
> - a secondary DNS at a different location(server park) pointing our domain
> at a smaller cluster at the same location

> The idea is then, that in case our primary host is down all traffic will go
> to the second cluster as the secondary nameserver takes over for the
> unavailable primary. This is of course pointless if our DNS information is
> cached all over the internet for e.g. 24 hours, so it is essential that we
> can set TTL to for example 5 minutes and that at least a majority of DNS
> servers respect this TTL. Secondly, we will have to scale our secondary
> cluster according to the load which it will receive (from the secondary DNS
> server).

This idea is broken. 
Hint - how is a NS for a certain domain found for other NS ?



> /Jakob




-- 
Peter Håkanson         
        IPSec  Sverige      (At the Riverside of Gothenburg, home of Volvo)
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