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From "Jacob Coby" <jc...@listingbook.com>
Subject Re: [users@httpd] Web server replication
Date Thu, 12 Sep 2002 17:04:54 GMT
> Please could someone shed some light on how web server
> replication/resilience is performed.
>
> What I am attempting to do is have one machine set up as a default web
> server, but if anything should happen to it then a second machine should
> come into play (but with content identical to the first server). So in
> other words how do I keep the two web server's content in sync?

If all you need is a hot standby server, just write a script to bring down
the interface on the primary server, and another to bring up the interface
on the secondary server.

If you want true load balancing, try something like
http://www.linuxvirtualserver.org/ or pirahna (RedHat's implementation of
the lvs).

To keep them in sync, use a tool such as rsync/rdist along with cron, to
have changes automatically propigate.  If you wanted to get really fancy,
you could write a script that checks the md5sum of you website against the
last known replicated value, and only rsync when this value changes.

Another option is to use 4 servers: the LVS server, two webservers, and a
storage server (with at least raid 1).  The storage server exports your
website to the 2 webservers via NFS, and the webservers handle serving up
the data.  This would have to be on a 100T network, or ideally a 1000T
connection if you are serving up huge amounts of database driven data.

You can use one of the webservers as a LVS server, but then you have a
single point of failure again if that webserver goes down.  Same for the
storage server.

-Jacob
http://www.listingbook.com


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