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This document describes when and how to use name-based virtual hosts.
See also: Virtual Host examples for common setups, IP-based Virtual Host Support, An In-Depth Discussion of Virtual Host Matching, and Dynamically configured mass virtual hosting.
IP-based virtual hosts use the IP address of the connection to determine the correct virtual host to serve. Therefore you need to have a separate IP address for each host. With name-based virtual hosting, the server relies on the client to report the hostname as part of the HTTP headers. Using this technique, many different hosts can share the same IP address.
Name-based virtual hosting is usually simpler, since you need only configure your DNS server to map each hostname to the correct IP address and then configure the Apache HTTP Server to recognize the different hostnames. Name-based virtual hosting also eases the demand for scarce IP addresses. Therefore you should use name-based virtual hosting unless there is a specific reason to choose IP-based virtual hosting. Some reasons why you might consider using IP-based virtual hosting:
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Related Directives DocumentRoot NameVirtualHost ServerAlias ServerName ServerPath VirtualHost |
To use name-based virtual hosting, you must designate the IP
address (and possibly port) on the server that will be accepting
requests for the hosts. This is configured using the NameVirtualHost directive.
In the normal case where any and all IP addresses on the server should
be used, you can use * as the argument to
NameVirtualHost. (NameVirtualHost * will
work only in version 1.3.13 and later.) Note that mentioning an IP
address in a NameVirtualHost directive does not
automatically make the server listen to that IP address. See Setting which addresses and ports Apache uses
for more details. In addition, any IP address specified here must be
associated with a network interface on the server.
The next step is to create a <VirtualHost> block for
each different host that you would like to serve. The argument to the
<VirtualHost> directive should be the same as the
argument to the NameVirtualHost directive (ie, an IP
address, or * for all addresses). Inside each
<VirtualHost> block, you will need at minimum a ServerName directive to
designate which host is served and a DocumentRoot directive to
show where in the filesystem the content for that host lives.
For example, suppose that both www.domain.tld and
www.otherdomain.tld point at an IP address
that the server is listening to. Then you simply add the following
to httpd.conf:
NameVirtualHost *
<VirtualHost *>
ServerName www.domain.tld
DocumentRoot /www/domain
</VirtualHost>
<VirtualHost *>
ServerName www.otherdomain.tld
DocumentRoot /www/otherdomain
</VirtualHost>
You can alternatively specify an explicit IP address in place of
the * in both the NameVirtualHost and
<VirtualHost> directives. The IP address is
required in version 1.3.12 and earlier.
Many servers want to be accessible by more than one name. This is
possible with the ServerAlias
directive, placed inside the <VirtualHost> section. For
example if you add this to the first <VirtualHost> block
above
ServerAlias domain.tld *.domain.tld
then requests for all hosts in the domain.tld domain
will be served by the www.domain.tld virtual host. The
wildcard characters * and ? can be used to match names. Of course,
you can't just make up names and place them in ServerName
or ServerAlias. You must first have your DNS server
properly configured to map those names to an IP address associated
with your server.
Finally, you can fine-tune the configuration of the virtual hosts
by placing other directives inside the
<VirtualHost> containers. Most directives can be
placed in these containers and will then change the configuration only
of the relevant virtual host. To find out if a particular directive
is allowed, check the Context of the
directive. Configuration directives set in the main server
context (outside any <VirtualHost> container)
will be used only if they are not overriden by the virtual host
settings.
Now when a request arrives, the server will first check if it is
using an IP address that matches the NameVirtualHost. If
it is, then it will look at each <VirtualHost>
section with a matching IP address and try to find one where the
ServerName or ServerAlias matches the
requested hostname. If it finds one, then it uses the configuration
for that server. If no matching virtual host is found, then
the first listed virtual host that matches the IP
address will be used.
As a consequence, the first listed virtual host is the
default virtual host. The DocumentRoot from the
main server will never be used when an IP
address matches the NameVirtualHost directive. If you
would like to have a special configuration for requests that do not
match any particular virtual host, simply put that configuration in a
<VirtualHost> container and list it first in the
configuration file.
As mentioned earlier, there are some clients who do not send the required data for the name-based virtual hosts to work properly. These clients will always be sent the pages from the first virtual host listed for that IP address (the primary name-based virtual host).
There is a possible workaround with the ServerPath
directive, albeit a slightly cumbersome one:
Example configuration:
NameVirtualHost 111.22.33.44
<VirtualHost 111.22.33.44>
ServerName www.domain.tld
ServerPath /domain
DocumentRoot /web/domain
</VirtualHost>
What does this mean? It means that a request for any URI
beginning with "/domain" will be served from the
virtual host www.domain.tld This means that the
pages can be accessed as
http://www.domain.tld/domain/ for all clients,
although clients sending a Host: header can also
access it as http://www.domain.tld/.
In order to make this work, put a link on your primary virtual host's page to http://www.domain.tld/domain/ Then, in the virtual host's pages, be sure to use either purely relative links (e.g., "file.html" or "../icons/image.gif" or links containing the prefacing /domain/ (e.g., "http://www.domain.tld/domain/misc/file.html" or "/domain/misc/file.html").
This requires a bit of discipline, but adherence to these guidelines will, for the most part, ensure that your pages will work with all browsers, new and old.
See also: ServerPath configuration example
