*BSD News Article 98952


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From: "Jordan K. Hubbard" <jkh@FreeBSD.org>
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: Upgrade Strategy on Heavily-Used System?
Date: Thu, 03 Jul 1997 16:37:20 -0700
Organization: Walnut Creek CDROM
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To: "John R. Haggis" <haggis@cesium.com>
Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:43910

John R. Haggis wrote:
> My question:  How do I upgrade without bringing the system down for a
> day, backing up all user files, rebuilding and reinstalling on a clean
> disk, reconfiguring all the servers, and reinstalling the user files?
> This is the only obvious way I can see for a comprehensive upgrade.
> Unfortunately, it is NOT an option.  I have dozens of users here and in
> Japan who use the machine daily!

There is one way and only one way to do this.  Others may suggest more
dramatic alternatives, but all involve significant degrees of risk and
usually at least some amount of downtime, either of which would be
unacceptable in your case.

The way to do this is simple:  You install another box with the target
OS and software, copying the user files over and using DNS tricks to
"phase" the box into production, e.g. you might bring web services over
to it first and then gradually redirect the other services as things
appear stable.  Once everything has been migrated away from the old
machine and you're sure that all the relevant user files have been
saved, you can shove it out of the way and use it for the next upgrade.

If things go wrong in the middle of an upgrade using this method, you
simply and quickly go back to your original box and the customers don't
see any interruption of service.  I wouldn't do it any other way, and
hang the cost of a second system.  My time is worth a lot more than the
cost of another PC, not to mention the sheer aggro of a failed upgrade
and customers who (quite rightly) now want my head on a stick - life is
too short.

-- 
- Jordan Hubbard
  FreeBSD core team / Walnut Creek CDROM.