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

[Sam Pointer]

Jacob: 

I am also considering something very very similar - I would be very
interested in sharing any information you have. What I am trying to achieve
is a swap between 2 different leased lines from two different providers if
connectivity is lost on one line (both lines to be used under normal loads).
We plan to reload the nameserver with records containing IP addresses
routable only down the "good" line if something does go wrong.

regards; Sam.

-----Original Message-----
From: Jakob Bak [mailto:Jakob at Bak.com]
Sent: 22 March 2002 16:01
To: comp-protocols-dns-bind at isc.org
Subject: Using a low TTL to enable a fail-over cluster?


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

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).

/Jakob




This email and any attachments are strictly confidential and are intended
solely for the addressee. If you are not the intended recipient you must
not disclose, forward, copy or take any action in reliance on this message
or its attachments. If you have received this email in error please notify
the sender as soon as possible and delete it from your computer systems.
Any views or opinions presented are solely those of the author and do not
necessarily reflect those of HPD Software Limited or its affiliates.

 At present the integrity of email across the internet cannot be guaranteed
and messages sent via this medium are potentially at risk.  All liability
is excluded to the extent permitted by law for any claims arising as a re-
sult of the use of this medium to transmit information by or to 
HPD Software Limited or its affiliates.