Re: application online upgrade strategy

On 23.05.2007 18:55, lest mitsui wrote:
> Does anyone have an idea on where to turn for
> information/research papers on online application
> upgrades? I am well-versed in offline upgrades, but I am now faced with customer requirements for transparent software upgrades of our application server/services -- and what possible solutions are there for software upgrades with co-requisite schema changes.

Use Slony and/or DBLink for application and PG upgrades, and a usual
Linux-HA active/passive 2 node cluster to manage all other upgrades (OS,
other applications, whatever..).

You use Slony/DBLink to transparently convert your data near real time
from your old schema to the new.

Zero downtime is still an illusion, but you might manage to get it down
to a few seconds. Always test and verify everything on clone systems
first. So instead of one server you might require 4 of them now. Also be
aware that a HA setup is not done over a weekend. I'd plan 3-4 months to
get everything perfectly working and tested. And still.. every online
application upgrade will require a huge amount of prearrangement work
and testing on clones/snapshots. Oh, and be sure to have a good backup
concept. If something goes wrong during an update at any point, you have
a few seconds to restore the state of the system as it was before (If
you can afford to lose any transactions at all).

--
Regards,
Hannes Dorbath