Thanks to James Carter for informing me that Microsoft has released a new tool that allows ISP´s to create more than 100,000 web sites on a single IIS 5 server.

Internet Service Providers (ISPs) are often interested in providing their customers with free or low-cost Web hosting services and domain parking as part of the services that customers receive with an Internet access account. Some ISPs also offer free Web sites, which are subsidized by advertisements that are displayed as clients access various Web pages. Because the volume of requests to such Web sites are typically very low, an ISP can host large numbers of sites on a single server if content is limited to static HTML pages. However, the practical limit for IIS 5 is 5,000 sites per box due to overhead related to site configuration. The Scalable Hosting Solution (SHS) sample application enhances the ability of IIS to host many thousands of sites using an ISAPI filter that provides an alternate approach to configuring individual sites in the metabase.

The SHS ISAPI filter uses a single Web site and virtual root (vroot) in IIS and rewrites the URLs of incoming requests and maps the requests to individual subdirectories under that vroot. Several forms of remapping are supported, including vanity sites (e.g. http://www.bigisp.com/davidjones) and three-tier domains (e.g. http://www.davidjones.com). Site content and metabase configuration for each site are stored in separate directories. This structure provides security because users are only able to access metabase configuration through COM interfaces and cannot directly edit metabase configuration files. SHS also offers high scalability because the ISAPI filter locates the site content and metabase configuration via a mapping algorithm, instead of through the metabase. Finally, SHS prevents the problems associated with too many files in a directory as the number of site directories increase because the site content and metabase configuration directory is created under a three-tier hierarchical directory tree, and the location of files within a directory tree depends upon the first three letters of the site name.

Read more | Administration Guide