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replicating, balanced web-server with *write* access?


Much is written about High-Availability servers but I still didn't find a 
good solution how to build two load-balanced webservers _without_
connecting them both to one RAID (single point of failure).

The problem with balancing between two servers is that the might host 
web-servers that could write a file on system A and then reading this file
(status file or whatever) on system B immediately before e.g. rsync could 
transfer it. In the worst case writing/reading could happen for two different
connection so that even connection based balancing wouldn't work.

For now I have three ideas:
1. forget about load balancing and do one-way balancing i.e. having one
   primary and one minutely synced backup. In a case of a failure the 
   backup would take over the service and even if there's a little loss it
   only occures at failures.
2. use network attached storage. To avoid another single point of failure
   you then would have to take two file servers and a protocol (NFS wont
   need) to realize this. Maybe at least IP takeover and forced reconnection
   NFS clients.
3. Forget about writing anything to disk - apart from FTP uploads
   everything will have to be written to database. But tell that your

The ideal solution would be a network filesystem like www.inter-mezzo.org 
but it does not appear to be really mature and tested in real life

So any idea?



Christian Hammers    WESTEND GmbH - Aachen und Dueren     Tel 0241/701333-0
ch@westend.com     Internet & Security for Professionals    Fax 0241/911879
           WESTEND ist CISCO Systems Partner - Premium Certified

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