Re: Webserver Redundacy
On Wed, Feb 28, 2007 at 11:16:20AM +1100, Craig Sanders wrote:
> LVS avoids all that because there is no changeover.
of course, there's a catch (isn't there always :). and the catch is that if
you need to store any data (e.g. session info) between browser requests,
you have to do in such a way that it is available no matter which server
happens to serve any particular request. mostly this means storing your data
in a database rather than on a filesystem.
to illustrate:
user fred visits your site, and fills in a form. he is served by
real-server "web1". you record the data in some way. an hour later he
returns, but this time he is served by real-server "web2". unless the saved
data is shared somehow (e.g. sql database), web2 will know nothing about fred
or the data he already supplied.
the easiest ways to do this is with a shared or network filesystem (be careful
of file locking), or in a database (let the db handle locking issues).
craig
--
craig sanders <cas@taz.net.au>
"God is as real as I am," the old man said. My faith was restored, for
I knew that Santa would never lie.
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