Limitations of Virtual Hosting

Virtual hosting or subhosting is a great feature of the Virtual Servers System. However, there are some limitations to this capability which you should understand. These limitations include the following:

  1. Virtual subhosting was 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 they will not be able to view their sites, nor other sites which are using Virtual Subhosting. However, considering that together Netscape and MSIE have 90-95% of the market share, this is generally not major a problem. Nonetheless, it is good to be familiar with this limitation.

  2. A Virtual Server is capable of handling 30,000 to 50,000 hits (assuming hits generally request about 5 kb of data) per day. That is not "visitors", rather hits or requests for files. For instance, if you have 5 subhosted domain names, each which is trying to accommodate 10,000 hits per day (which really isn't that much if you have a graphically intensive page; one request for a .gif or .jpeg equals one hit!) there will likely be a problem. This "slowdown" will affect all of your clients on the Virtual Server you are using to subhost.

    When a slowdown occurs a wise Reseller will properly "manage" his or her Virtual Server by reducing the number of subhosts on the Virtual Server by either upgrading one of the especially high traffic virtual hosted sites to its own Virtual Server or by moving some subhosts to a less busy Virtual Server. Either way, proper load balancing is a science that a Reseller must have a feel for in order to succeed with serious virtual subhosting.

  3. A Virtual Server can only host a finite number of Virtual Hosts due to performance reasons. Consider the following recommendations when deciding how many Subhosts to place on a single Virtual Server.

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

  4. 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.

  5. A Virtual Server can only support a single Digital Certificate. This can make the use of SSL difficult since all subhosts must use the same Digital Certificate and only one domain name can be associated with a Digital Certificate.

  6. A virtual subhost does not have telnet access to the Virtual Server.

  7. Microsoft® FrontPage® 98 FrontPage® 2000 child webs will work with subhosting.

  8. There are some limitations to the e-mail capability of subhosts, namely how the Virtual Server intreprets e-mail addresses. For instance, if you send an e-mail to "john@abc.com" and "john@xyz.com" the Virtual Server will view these as the same address. This is because to the Virtual Server, "john@abc.com" and "john@xyz.com" both resolve to "john@192.41.5.2" because both domain names resolve to the same IP address. However a way to get around this limitation by using a utility titled "virtmaps". You can find out more information about "virtmap" setup in the in the Virtual Email Address Mapping Section.

  9. It is important to understand that giving cgi-bin access to your virtually subhosted clients is a potential security risk. This is because the CGIs your customers upload and execute have all of the rights and privileges of the CGIs 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.

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