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

Tres Seaver tseaver at zope.com
Wed Oct 6 17:54:19 EDT 2004


Paul Winkler wrote:
> On Wed, Oct 06, 2004 at 02:35:50PM -0500, Ausum Studio wrote:
> 
>>What are the best, or most used fail-safe redundancy practices suitable to
>>Zope? More in detail, I'm working on a Zope-based system that will store the
>>data inside the ZODB, and one of the design requests is that given an
>>unrecoverable hardware crash, the system could continue running using a
>>mirror installation with the latest backup (not later than half an hour or
>>even less.)
>>
>>APE looks like the way to go since it allows the use of standard backup
>>software, but you may have tried other possible solutions for a problem like
>>this. According to your experience how would you accomplish it?
> 
> 
> I haven't actually implemented either of these, but:
> 
> You could spend some $$ and get ZRS from zope corp which
> IIRC might let you do automatic failover without loss of service.
> Not sure though.

For full QoS, ZRS out of the box would only support "warm" failover (it 
would require downing the secondary and bringing it back up as a 
primary).  We have experimented with using 'heartbeat' to automate that, 
but haven't deployed it in production.

If having the appservers degrade to read-only mode on primary failure is 
a sufficient QoS, ZRS does that automatically.

> You could also use DirectoryStorage and frequently replicate to a
> backup storage server.  The backup can't actually serve to ZEO clients
> as long as you're replicating to it, but you might be able to come up with
> some scripts that automatically start a live storage process on
> the backup if the primary fails.  
> Reverting to the primary server might have to be
> a largely manual process.

Right.  'heartbeat' might help there, too.

Tres.
-- 
===============================================================
Tres Seaver                                tseaver at zope.com
Zope Corporation      "Zope Dealers"       http://www.zope.com



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