Sitecore automatically parses the incoming HTTP request to resolve which site information it should use.
The approach described in the present article works well for solutions which serve few sites and where the list of sites does not change often.
Some installations, however, need to support many sites or change the list of supported sites often. In this case, changing the web.config file for each new site is unacceptable.
A custom module for defining and resolving sites can be built in Sitecore, thus allowing the avoidance of the web.config file change for each site added. The Multiple Sites Manager module found in the Shared Source Library provides such solution. The main idea is to store the custom sites in the content tree instead of the web.config file. The module allows storing the sites both in web.config and the content tree.
Go to Multiple Sites Manager page.