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Due to the increasing popularity, size, and activity of the
World Wide Web in general, and www.niu.edu in particular,
the web server on this machine (corn) is overloaded and not
performing as well as we would like. We are taking two
paths to improved performance for web pages hosted by corn.
First, we are working on the installation of and conversion
to a replacement for the machine.
In the interim, to provide improved performance and reduced
load on the old machine, we are planning to install a
reverse proxy (web accelerator, or cache) server on the
network. This machine will be configured so that it provides
a transparent cache of the data currently being served up by
the web server on www.niu.edu. By caching the data, the load
on the real web server should be dramatically reduced, and
performance improved.
For those interested in the configuration details, the cache
server will be a Compaq ProLiant 1600, with 256M RAM and 27G
disk space. It will have at least one 100mbit connection to
the NIU backbone. It will be running Novell's NetWare5
operating system and BorderManager Enterprise ver. 3.0. The
BorderManager software will be configured for web
acceleration and caching. The DNS entry for
"www.niu.edu" will be changed to point users to
the cache server.
When a URL is passed to the cache server (as www.niu.edu)
requesting a web page, the cache server will first check its
cache to see if the page is already in cache, and has not
been in cache past the expiration time. If the data is
already in cache, it will be sent to the requesting web
browser immediately. If the data is not in cache, the cache
server will have to request it from the real web server,
then send it to the requesting browser. If the data is in
cache, but has been there for more than 6 hours, the cache
will first validate it with the real web server, then either
send it to the requesting browser (if unchanged), or request
the updated copy from the real web server before sending it
to the browser.
The obvious question that this raises is "how do I
update my web page if it is going to be in a cache"?
There are three possible scenarios:
The "Reload" request from the browser will always cause
the cache server to request a new copy from the real web
server. If you have updated a web page on corn, use the
"Reload" function of your browser to retrieve it and the
cache will be updated.
Waiting for the cache timeout to expire (6 hours).
Use of the "expires" HTML Meta tag. Use of this tag with
a timeout value less than 6 seconds will be ignored by
the cache server. Timeout values greater than six hours
will be ignored also, and the cache will continue to
timeout at six hours.
If you want to see how this works in practice, a test system
has been set up at http://131.156.57.55. This machine is
sufficient to provide functional testing, though its
performance is limited by its 10mbit network connection.
Note that DNS has not been changed, so any web page with
"www.niu.edu" in the URL will go to the real web
server, not the cache. Only relative links will go through
the cache.
Questions and comments to:
David Gersic dgersic@niu.edu