[gnhlug-announce] SLUG "problem solution" meeting Monday 7/14 7pm at UNH in Morse 301

Dan Coutu coutu at snowy-owl.com
Thu Jul 10 07:31:52 EDT 2003


On Wed, 2003-07-09 at 21:21, Bruce Dawson wrote:
> On Wed, 2003-07-09 at 14:37, Robert Anderson wrote:
> > ...
> > I'm still open for problems to work on.  If you have something you've
> > been trying to do and would like to have the groups input, please send
> > an email or be ready to explain your problem to the group on Monday.
> >...
> 
> Well, something I've been struggling with lately is how to plan a site
> for upgrading with minimal downtime (i.e. just the time required to
> reboot).
> 
> One thing that we've looked at is having two computers with identical
> configurations - software and hardware, and use LVS (or some equivalent)
> to switch the web and mail services to the other system when one goes
> down. However, this falls apart rather quickly - databases need to be
> duplicated, resync-ing things like log files are a royal pain, ...
> 
> I'm mostly wondering how other sites handle this with minimal hardware
> and proprietary software investments.
> 
> --Bruce

The amount of downtime you'll have is proportional to the amount of
money you spend. I'm sure you realize this and were just hoping to get
around it somehow.

The upgrade operation is rather complex. As you point out things can get
sticky. My experience is that the time needed to synchronize databases
can be minimized but not completely avoided. Much of the rest of the
system can be duplicated in advance. If you roll your logs as part of
taking the primary system offline then you can simply copy the old
versions to the new system. It is then no different than a normal log
rolling operation.

The DB resync time I've minimized in the past by using a full DB backup
from earlier in the day to populate the standby DB and then updating it
with only the newer data from the DB at the time of switchover. This
often results in a downtime measured in minutes rather than an hour or
more. The specific methods to use for this will of course depend on the
database being used.

-- 

Dan Coutu
Managing Director
Snowy Owl Internet Consulting, LLC
http://www.snowy-owl.com/







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