[CentOS] High Availability using 2 sites

Bryan J. Smith thebs413 at earthlink.net
Thu Jan 5 17:34:10 UTC 2006


Todd Reed <treed at astate.edu> wrote:
> I agree, BGP is important to route the IP's, but I've been
> exploring this same option with a different thought.

I guess you missed my point.  It's _not_ just a matter of
using BGP for your dynamic routing.  It's a matter of getting
an assigned, autonomous system number so the Internet
addressing your multiple networks as the same network.

[ There's a lot more to the Internet than just IPs ;-]

That's the proper way to do it.

> I'd like to hear what others say about this!

I also made the suggestion to enable 1-to-1 NAT at each
facility.  Should the servers on one site go down, your
1-to-1 NAT devices would redirect requests to servers at the
other site.

That doesn't require an additional, "external"
registration/administration.  Of course it means packets are
now routed to your first site first, then your second site,
so if the first site is wiped out (with no equipment), that
doesn't help you.

> Here is my plan (although not implemented or tested) for
> Web Services.
> At our main data center we have the primary DNS server and
> our primary web server.  The remote location houses the
> secondary DNS server and our secondary web server.  Also at
> that second location is "hidden" master DNS server.
> .. cut ...
> That is the theory in a nutshell.  I've read that this is
> possible, but I haven't had a chance to test it.

The problem with the theory is that names are cached all over
the Internet.  That's why DNS server/name changes don't do
squat when it comes to failover.

Now you could _consider_ setting a very low time-to-live
(TTL) on your servers -- like 5 minutes.  But that doesn't
always work either.

> What do others think about this?  This is no substitution
> for BGP, but for those that don't run BGP or need to
re-route
> the IP networks, this may work.

Again, it's _more_ than just BGP.  ;->

You have to modify how the Internet sees you.
Not just what you provide to the Internet.  ;->

That's a key distinction that most people don't consider.

-- 
Bryan J. Smith     Professional, Technical Annoyance                      b.j.smith at ieee.org      http://thebs413.blogspot.com
----------------------------------------------------
*** Speed doesn't kill, difference in speed does ***



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