Limitations of Virtual Hosting

1. Non HTTP/1.1 browsers
   Virtual subhosting is made possible by the introduction of HTTP/1.1. In order to view subhosts you must have a browser which is HTTP/1.1 compliant. Generally speaking, subhosts are supported by Netscape Navigator 2.0+ and MSIE 3.0+. Any other browser that is HTTP/1.1 compliant will be able to access virtual subhosted servers.

   If your clients are using an older browser which is not HTTP/1.1-compliant then they will not be able to view their sites, nor other sites which are using virtual subhosting. The likelihood of someone using an non HTTP/1.1 browser is very rare, but nonetheless,you should be familiar with this limitation.

2. Server Hits
   A Virtual Server is capable of handling 30,000 to 50,000 hits per day. "Hits" are not "visitors", but rather requests for files.For example, one web page with 20 graphics equals 21 hits, or 21 file requests.
   
   If you have 5 subhosted domain names, each which is trying to accommodate 10,000 hits per day, server performance will be adversely affected. This "slowdown" will affect all of your clients on the Virtual Server you are using to subhost.

   Proper load balancing is a science that a sysadmin must learn in order to succeed with serious virtual subhosting. When a slowdown occurs due to server overload, the system administrator will properly "manage" his or her Virtual Server by reducing the number of subhosts on the Virtual Server by:
   

   1. upgrading one of the especially high-traffic virtual hosted sites to its own Virtual Server;
      
   2. moving some subhosts to a less busy Virtual Server; or
      
   3. upgrading the Server type to a more powerful Server.
   
   
3. Domains
   For performance reasons, we have established recommendations with regard to the number of virtual hosts you should place on a single Virtual Server System. Keep in mind that the purpose of these recommendations is to ensure continued performance of your server and the other sites that you host.

   Server A:   around  5 low-volume subhosts
   Server B:   around 25 low-volume subhosts
   Server C:   around 60 low-volume subhosts
   
   

   We cannot guarantee the number of virtual hosts you will be able to successfully host since each site uses a different amount of server resources. It may be that you can only host one other virtual host before your resources are exhausted on your Virtual Server. It is up to you to monitor virtual hosts and upgrade high load virtual hosts to their own Virtual Servers.

4. Single IP Address
   Virtual subhosting obviously uses the resources of a single Virtual Server to accommodate the needs of multiple web sites. Among the resources that are shared is the single IP address that is associated with the Virtual Server. Search engine "spiders" which are not HTTP/1.1 compliant will not be able to index the sites. Most major spiders and search engines are now HTTP/1.1 compliant, however, and have been for several years.

5. Single Digital Certificate
   A Virtual Server can only support a single Digital Certificate. This can make the use of shared SSL difficult since all subhosts must use the same Digital Certificate and only one domain name can be associated with a Digital Certificate.
   
   There is a feasible workaround, however. Thawte allows wildcard digital certificates, which means you can provide a secure connection for all your clients by offering them a canonical domain. Thus, "clientA.you.com," "clientB.you.com," and "clientC.you.com" may all share the same digital certificate. VeriSign, another certifying authority, does not provide wildcard digital certificates.

6. Single Telnet Account
   A virtual subhost does not have Telnet access to the Virtual Server. Only the Virtual Server Administrator receives a telnet account. This provides a more secure environment for your server as a whole.

7. Microsoft FrontPage Extensions
   Microsoft® FrontPage® 97 child webs will not work within a virtual subhosting environment. Please note that Blue Reef only supports FrontPage 2000 extensions; any other FrontPage product you install on your Virtual Server is at your risk.

8. Email Addresses
   There are some limitations to the email capability of subhosts, specifically how the Virtual Server interprets email addresses. Blue Reef provides, however, a way to get around this limitation by using a proprietary utility called virtmaps.

9. CGI-security
   It is important to understand that giving cgi-bin access to your virtually subhosted clients is a potential security risk. This is because the CGI scripts your customers install and execute have all of the rights and privileges of the CGI scripts you execute. Therefore, it is possible for a virtually subhosted client, which has been granted CGI privileges, to read or remove any file in your directory hierarchy. Moreover, it is possible for a malicious subhosted client to crack weak passwords and gain shell access to your Virtual Server. Please see our document, Virtual Subhosting and Security Issues for more information.