Using the correct name for the WWW server and the MySQL server
Using a cluster of webserver machines
In order to provide resilience and a fast service, CIS uses a cluster of webserver machines for handling the requests to
www.dur.ac.uk. So one request to
www.dur.ac.uk might go to one webserver machine whereas the next might go to some other webserver machine.
Handling sessions across a cluster of webserver machines
Normally, connections to a webserver are stateless, i.e., in a series of connections to a webserver, no information is retained from one connection to the next. However, increasingly, people are finding ways in which information is retained from one connection to the next. Some of the ways in which this can be accomplished include: cookies, hidden fields in WWW forms, additional information in URLs, information stored in the webserver process (e.g., the session facility of PHP), information stored in databases. For some of these techniques, all the requests belonging to the same session need to be sent to the same webserver machine.
Since the upgrade of the web service in September 2007, all requests to
www.dur.ac.uk pass through a load balancer, one of whose roles is to ensure that all requests from any particular user's web browser during a particular session are passed to the same cluster member. This is implemented using cookies, and provided the user's browser is configured to accept cookies from
www.dur.ac.uk, no further configuration is required.
Prior to September 2007, it was necessary to use the server name
www-same.dur.ac.uk, instead of
www.dur.ac.uk, to contact a specific webserver machine (for example, if you use PHP's
$_SESSION variables). This is no longer necessary, and the name
www-same.dur.ac.uk is now deprecated, and simply redirects to
Accessing the MySQL server
The MySQL service runs on separate computers from the web service. All accesses to the MySQL server (e.g., a call of
mysql_connect in a PHP script, a DSN for access using ODBC) must be written to refer to the appropriate server, not
www.dur.ac.uk. For most end user MySQL databases, the server is
mysql.dur.ac.uk. If you have been given a MySQL account on a different server, you must use that name instead in PHP scripts, etc.
If you have any queries, please contact the IT Service Desk (firstname.lastname@example.org ) on extension 41515.