[Zope] Static fail-over

[sean.upton@uniontrib.com]

This might be hard to do with a load-balancer setup alone, because the
balancer would need to know when to fail over (and not just in the case of
Zope stopping to respond); another similar solution might be more along the
lines of IP takeover software like Heartbeat (linuxha.org) or Failsafe
(oss.sgi.com) that makes the "safe" hot-backup Zope box takeover the
identity of the "corrupted" primary Zope box, assuming that you have a
monitoring setup on the backup to audit the integrity of your primary Zope
service/data.

The advantage that this has over a load-balancer approach is that you can
write your own custom monitors/audit-scripts to determine/test the criteria
for a failover to a much more fine-grained degree than just refused HTTP
connections.  Linux Failsafe has service monitoring setups, while you would
use Mon or something similar in conjunction with Heartbeat.

I would suggest a combination of Squid in front and heartbeat or Linux
Failsafe on Zope boxes (either independent ODB or with ZEO) nodes in this
case.

You could use ZEO+ExternalMount or ZSyncer to copy content to your second
Zope if you had 2 antonymous Zopes.  Squid (or any other reverse-proxy or
load-balancer) would then obey any IP address takeover from a hot-backup
node happening via gratuitous/unsolicited ARP.

Sean

-----Original Message-----
From: Anthony Baxter [mailto:anthony@interlink.com.au]
Sent: Monday, January 21, 2002 4:18 PM
To: Terry Hancock
Cc: zope@zope.org
Subject: Re: [Zope] Static fail-over


>>> Terry Hancock wrote
> I have a Zope site which I'm doing a lot of development
> on, and all internal safeguards aside, I feel there's a
> significant chance of wrecking Zope in the process. Then
> it might take anywhere from hours to days to get it back
> up again.

Aside from making sure you have a sane development and 
deployment process, you could consider using a load balancer, 
set up to point to the primary (development?) server normally, 
and switching it to a backup one when things fail. There's 
a bunch of hardware or software ones - I've used both. Hardware's
better, obviously, but you could consider something like the 
tool 'balance' from balance.sf.net

Anthony

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