[Zope] zope on shared disk

[Martijn Pieters]

From: kdie [mailto:webheads@ns1.emedia.com.my]
> >
> >I don't know about Samba, but Jim Fulton warns against _accessing_
> >Data.fs over NFS. It is a surefire way of corrupting it.
> >
> 
> thanks for the warning.
> 
> >About sharing the Data.fs between multiple Zope processes: 
> Don't do it,
> >it doesn't work. The Data.fs file is locked by the Zope 
> process using it
> >for a reason.
> >
> >For load balancing like this yuo will have to go with either ZEO, or
> >some form of XML-RPC based load balancing (ie. write your own).
> >
> i'm currently loking at eddie(http://www.eddieware.org) to do the load
> balancing for me.  eddie can do a lot of things.  one of them 
> is redirecting
> request according to METHOD.  so, if it's a post, i'll 
> redirect it to one
> particular server.  if it's a get, it goes everywhere.  i 
> would think that
> rsync can update data from the machine that handles post 
> request to other
> machines.  so, in a sense, i'm using one Data.fs,  but 
> distribute all GETs
> to all available servers.  but i'm not quite sure of the 
> update frequency.
> 
> 
> comments, pointers?

You can't use rsync on Data.fs when Zope is running though. You will
have to shut down both the source Zope (to prevent writs during sync)
and the target Zope. The latter because FileStorage wasn't designed to
have it's datastore shift around underneath it.

What do you need load balancing for anyway? Is it for scalability, or
for reliability? 

If you want scalability, surely the cost for ZEO can be justified? Also,
do realize that Zope on a single machine can scale pretty awesome. We
recon ZEO is only necessary for the absolute top range of websites.
Zope.org runs on a single machine, just flexing its muscles a bit on 2
million hits per month.

If you want reliability, why not have a second machine on standby, to
take over in case of failure? I am sure that tweaking FileStorage to
hold back from Data.fs for a backup wouldn't be that hard. This is not
strictly necessary either, you'd only miss the transaction or so. You
can then have the back-up Zope take over when a monitoring process deems
it necessary.

-- 
Martijn Pieters, Software Engineer 
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