Limitations of Virtual Subhosting
Virtual Subhosting is a great feature of our
Virtual Servers System. However, there are some limitations to this
capability which you should understand. These limitation include
Virtual Subhosting is made possible by the introduction of HTTP/1.1.
In order to view subhosted domains you must have a browser which is HTTP/1.1
compliant. Generally speaking, Virtual Subhosting is supported by Netscape
Navigator 2.0+ and MSIE 3.0+. Any other browser that is HTTP/1.1
compliant will be able to access a subhosted domain.
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
- 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
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.
- A Virtual Server can only host a finite number of Virtual Subhosts 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.
- 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.
- 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
- A Virtual Subhost does not have telnet access to the Virtual Server.
- Microsoft® FrontPage® 97 child webs will not work within a
Virtual Subhosting environment. (However, Microsoft®
FrontPage® 98 child webs will work with Subhosting).
- There are some limitations to the e-mail capability of Subhosts,
namely how the Virtual Server interprets e-mail addresses. For
instance, if you send an e-mail to "email@example.com" and "firstname.lastname@example.org"
the Virtual Server will view these as the same address. This is
because to the Virtual Server, "email@example.com" and "firstname.lastname@example.org" both
resolve to "email@example.com" because both domain names resolve to the
same IP address. However, we have developed a way to get around
this limitation by using a proprietary utility titled "virtmaps".
See our document, Providing E-Mail for Virtual Subhosts for more information.
It is important to understand that giving cgi-bin access to your
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 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.
see our document, Virtual Subhosting Security Issues for more information.
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