The application is configured in such a way that, when a new company is being created, the company admin needs to provide the subdomain name to be used. ie If the application is hosted on www.somedomain.com, then with the subdomain it will be subdomainname.somedomain.com. Based on the subdomain name, the code looks up the database to find out the company and based on that it can load the theme configured for the company. We use subdomain-fu plugin for supporting the subdomain feature in the application.
We also need to ensure that when a user types in a url with subdomain, then the request is forwarded to our server. For this, the DNS needs to be configured in such a way that *.somedomain.com points to one single IP. Apart from this, the web server needs to be configured in such a way that it can use the correct virtualserver.
More information here - http://ma.tt/2003/10/wildcard-dns-and-sub-domains/
Support for seperate domain - First, when you resolve the domain name it should point it to our IP. Second, Web server needs to be configured such that it handles the request for that domain. For this, 'ServerName' attribute (under VirtualHost Section) should list all the domains that the application support. Thirdly, the code needs to be modified in such a way that it can load the correct company.
