mod_rewrite

Here's a nice howto on using mod_rewrite under Apache and Lighttpd for temporary site outages. This tip will help you to disable a site for maintenance using mod_rewrite without redirecting url. Both Lighttpd and Apache webserver allows you to send this message to client using server side rewriting using mod_rewrite and php. This is useful if you are running popular database driven community or e-commerce website. Error 503 informs search engine that site is temporary out of service. A good idea

Apache's mod_rewrite module is a very powerful tool. And there's some neat tricks you can do with it. This trick involves forcing visitors and search engine robots to either the WWW version of your website, www.yourdomain.com, or the non-WWW version of your website, yourdomain.com.