[310] in Hesiod
Re: Info please
daemon@ATHENA.MIT.EDU (Amit Bhatiani)
Fri Jul 19 17:35:46 1996
Date: Fri, 19 Jul 1996 17:27:59 -0400
From: Amit Bhatiani <bhatiani_amit@jpmorgan.com>
Reply-To: amit@jpmorgan.com
To: asafier@csc.com
Cc: "Theodore Y. Ts'o" <tytso@MIT.EDU>, hesiod@MIT.EDU
Theodore Y. Ts'o wrote:
>
> Date: Fri, 19 Jul 1996 13:24:49 -0700
> From: Adam Safier <asafier@csc.com>
>
> Please send me info on how to get more info on using hesiod records in
> DNS.
>
> Specifically, I'm interested in using DNS to control the sequence of
> connect attempts to a primary and backup server. I'm NOT looking for
> round-robin load balancing. I want all connection attempts to go to the
> primary and only go to the secondary if primary is down.
>
> What you're looking for is a DNS issue, not a Hesiod issue --- and I
> don't know of any way to make DNS do what you're looking for. In
> general, DNS is architected to do round-robin load balancing, since in
> general's it's the right thing to do. I don't know off-hand of any way
> of forcing it to do something that's sub-optimal.
>
> - Ted
This is not even a DNS issue, but part of a larger issue which goes by
the name of high availability. The basic idea is that you connect your
primary and secondary machines two/three ways. One is the normal network
that they see each other on now, and you could possibly have a another
serial PPP link (if you don't have another network interface and would
not like to buy cards for the machines). The secondary machine is in
some form of single user mode. I say some form because you want to have
enough of the IP stack up to talk on the second PPP interface. This can
be done without bringing the main network interface up.
The secondary polls (ping or something similar) the primary every so
often (30 seconds) and decides if the primary is up or down. If it is in
fact down, the primary machines runs a script that brings up the main
network interface with the same IP address and hostname as the primary.
There are already commercial pieces of software that accomplish the
above.
Ted is right in that there is no way in DNS to solve this problem, but
that's because DNS is a name service, not a fault-tolerant system..:-)
hope this helps...
--amit
amit@jpmorgan.com
