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Computing and Information Services

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 www.dur.ac.uk.

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.

Queries

If you have any queries, please contact the IT Service Desk (itservicedesk@durham.ac.uk ) on extension 41515.