-----Original Message-----
From: fedora-list-bounces(a)redhat.com
[mailto:fedora-list-bounces@redhat.com] On Behalf Of Benjamin Franz
Sent: Wednesday, August 31, 2005 2:42 PM
To: For users of Fedora Core releases
Subject: Re: OT: DNS Failover
On Wed, 31 Aug 2005, Mike McGrath wrote:
> I'm curious about how others in the Fedora community are doing DNS
> failover. Specifically I have two sites, one primary (in a large
> city) and one secondary (out in the middle of nowhere).
The idea is
> that we'd host DNS out of the secondary site to use the web
servers in
> the primary site.
>
> My question is how are people handling outages at the main
site. If
> the primary site burns down or all the servers get stolen or
> something, is my only option a manual of the configs to
point from one to the other?
Slightly different than what you are asking, but we
multi-home our servers and placed a DNS server in each IP net
that returned _only_ the addresses for that subnet with a 900
second TTL. If we experience loss of IP on one pipe, that
renders the appropriate DNS server immediately unreachable
leaving only the good pipe's addresses being returned on
fresh queries while the stale unreachable addresses will
expire within 15 minutes.
This has worked very well for us in practice since the only
people impacted by a loss of a pipe are those who were
actually browsing our website servers via the down net in the
few minutes before the network outage while lettings us get
the good routing of being in two large tier-1 ISP routing
blocks (IP blocks of less than roughly a /18 just don't get
good routing IME because of backbone routers dropping small
subnet routes).
The problem with browsers caching IPs until the browser is
killed is not fully soluble via any DNS based system.
You can trade that for a portable block of IP addresses and
broadcast your routes, but you wil take a hit on normal
routing of a small subnet and on the reconvergence time of
routes after any failure.
There are no perfect solutions to this issue, AFAIK. Every
solution will have some failure mode that will impact you
more or less depending on your own requirements.
--
Jerry
Simple things should be simple, complex things should be possible.
- Alan Kay
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Thats an interesting way of doing it. I'll have to test that out too.
Thanks everyone for your comments.
-Mike