Re: svn update or rsync - which is best to update live files

On Sunday 27 Feb 2011, Chris Albertson wrote:
> OK, There is one way that works. I'd suggest using it.
>
> Most server OSes now have some way to make a virtual hoist. Solaris
> has zones, Linux has xen and there is VMware. The idea is that you
> build the new updated web site on a new virtual host. and then you
> test it. Once you like the tst results you swap IP addresses. You
> don't really want to go live with changes that are untested. The IP
> address is "atomic" in that the entire site goes live at once.
>
> BTW I've always liked the way Solaris does this in that you can have
> many "zones" each with their own IP address and file system but there
> is only one instance of the operating system running on the hardware.
> I always thought it a waste to have multiple copies of the same
> software in RAM, Sun solved that problem well.

I agree with your sentiment of not running untested configurations. The
deployment/environment setup should also be automated but with manual
oversight. That usually ensures all the steps to setup the environment are
followed but any issues can be handled at the time and not found out the next
morning. I guess it depends on how much business value the website brings
whether this is worth it :)

The ip address change might be atomic but this only works if there is no state
stored in the webserver/appserver. Any stateful sessions will be lost. Still,
for single physical server sites it's a nice approach. If there is more than
one physical machine involved then switching the loadbalancer policy would do
the same trick. This then relies on having enough spare server capacity to
support the two environments running at the same time though this could be
mitigated by doing the switchover at a quiet time. Sometimes it just isn't
possible to do an atomic switchover. For example, if a backend service also
needs to be updated or a database schema needs changed.

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