Re: [SAGE] number of eggs in a basket

[Steve Simmons <scs@lokkur.dexter.mi.us>]

On Fri, Jan 07, 2005 at 10:44:12PM +0100, Brad Knowles wrote:

> > With DNS, any machine that has a copy of the zone files and can do
> > virtual IP interfaces will work just fine . . .

> 	It depends on what you mean by "dies".  There are certain kinds 
> of failures that may happen within the application which would be 
> propagated to all the secondaries, and would not necessarily be 
> detectable by the monitoring system.

Of course, hence my 'hand wave, hand wave' earlier in the note.  The goal may
be seamless failover, but most places settle for very short minimum TTR - where
the R stands for 'Restore The Service', not 'Repair'.  And for DNS, the scheme
works -- if the DNS server really crashes, by the time you are convinced and put
the backup on-line, the ARP caches are largely timed out anyway.  Note also
that I'm not talking about secondary DNS servers, but restoration of a primary.
The backup machine has full copies of the zone files, so it can step into the
primarys IP address and most machines don't even know the service went away.

> 	Anyway, it all comes down to this -- YMMV.  You need to do the 
> cost/benefit analysis and figure out what works best for you.

Absolutely.

>     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
>     Assembly to the Governor, November 11, 1755
> 
>   SAGE member since 1995.  See <http://www.sage.org/> for more info.

Benjamin Franklin was a Sage member?  :-)
-- 
"There's a lot of my personality in my characters. I think that's why
 smart-asses are over-represented."
    Christopher Moore, in http://www.chrismoore.com/world_domination.htm