[Zope] Re: Fail-safe redundancy policies for Zope

[Paul Winkler]

On Thu, Oct 07, 2004 at 08:16:33AM -0500, Ausum Studio wrote:
> Paul, Tres, thanks for your responses.
> 
> Has anyone in the community tried any other non-standard way to accomplish a
> live backup, like to rely on a synchronization proccess auto-triggered by
> parallel installations?. I'd like to go this way as the first thing to try ,
> so now I'm looking for caveats from people who have alredy tried the Zsyncer
> way or the likes.  :)

Well, ZSyncer is an application-layer replication tool rather than
a database-layer replication tool. That is, it takes live objects
from one Zope and pushes them to another. This means that your two databases
are not really identical, they contain the same object data only for the
most recent revisions of the particular objects that you sync.

Some limitations:

*) It's slow for large data
*) It eats a lot of RAM for large objects
*) It's push-only - you cannot pull from the remote host to the local host.
*) It doesn't preserve history
*) it fails if you don't have exactly the same Products installed on 
both systems  .
*) it uses HTTP and basic auth, so it's up to you to ensure security
by using SSL or a VPN tunnel or whatever.
*) it frequently mis-reports whether objects are in sync or not
(it uses bobobase_modification_time, an inherently flawed approach).

But, it is often useful, and in fact I'm working on rolling out another
release with a lot of fixes/improvements (and probably new bugs
so there'll be a release candidate or two).
 
-- 

Paul Winkler
http://www.slinkp.com