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<parentdocument href="./">Virtual Hosts</parentdocument>

<title>Name-based Virtual Host Support</title>

<summary>

<p>This document describes when and how to use name-based virtual hosts.</p>

</summary>

<seealso><a href="ip-based.html">IP-based Virtual Host Support</a></seealso>

<seealso><a href="details.html">An In-Depth Discussion of Virtual Host Matching</a></seealso>

<seealso><a href="mass.html">Dynamically configured mass virtual hosting</a></seealso>

<seealso><a href="examples.html">Virtual Host examples for common setups</a></seealso>

<section id="namevip"><title>Name-based vs. IP-based Virtual Hosts</title>

<p><a href="ip-based.html">IP-based virtual hosts</a> 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.</p>

<p>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.</p>

<p>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 you are using equipment

that explicitly demands IP-based hosting. Historical reasons for

IP-based virtual hosting based on client support are no longer

applicable to a general-purpose web server.</p>

<p> Name-based virtual hosting builds off of the IP-based virtual host

selection algorithm, meaning that searches for the proper server name

occur only between virtual hosts that have the best IP-based address.</p>

</section>

<section id="alg"><title>How the server selects the proper name-based virtual host</title>

<p>It is important to recognize that the first step in name-based virtual

host resolution is IP-based resolution. Name-based virtual host

resolution only chooses the most appropriate name-based virtual host

after narrowing down the candidates to the best IP-based match. Using a wildcard (*)

for the IP address in all of the VirtualHost directives makes this

IP-based mapping irrelevant.</p>

<p>When a request arrives, the server will find the best (most specific) matching

<directive type="section" module="core">VirtualHost</directive> argument based on

the IP address and port used by the request. If there is more than one virtual host

containing this best-match address and port combination, Apache will further

compare the <directive module="core" >ServerName</directive> and <directive

module="core">ServerAlias</directive> directives to the server name

present in the request.</p>

<p>If you omit the <directive module="core">ServerName</directive>

directive from any name-based virtual host, the server will default

to a fully qualified domain name (FQDN) derived from the system hostname.

This implicitly set server name can lead to counter-intuitive virtual host

matching and is discouraged.</p>

<section id="defaultvhost"><title>The default name-based vhost for an IP and port combination </title>

<p> If no matching ServerName or ServerAlias is found in the set of

virtual hosts containing the most specific matching IP address and port

combination, then <strong>the first listed virtual host</strong> that

matches that will be used.</p></section>

</section>

<section id="using"><title>Using Name-based Virtual Hosts</title>

<related>

<modulelist>

<module>core</module>

</modulelist>

<directivelist>

<directive module="core">DocumentRoot</directive>

<directive module="core">ServerAlias</directive>

<directive module="core">ServerName</directive>

<directive module="core" type="section">VirtualHost</directive>

</directivelist>

</related>

<p>The first step is to create a <directive type="section"

module="core">VirtualHost</directive> block for

each different host that you would like to serve. Inside each <directive type="section"

module="core">VirtualHost</directive> block, you will need at minimum a

<directive module="core">ServerName</directive> directive to designate

which host is served and a <directive module="core">DocumentRoot</directive>

directive to show where in the filesystem the content for that host

lives.</p>

<note><title>Main host goes away</title>

<p> Any request that doesn't match an existing <directive type="section"

module="core">VirtualHost</directive> is handled by the global

server configuration, regardless of the hostname or ServerName.</p>

<p> When you add a name-based virtual host to an existing server, and

the virtual host arguments match preexisting IP and port combinations,

requests will now be handled by an explicit virtual host. In this case,

it's usually wise to create a <a href="#defaultvhost">default virtual host</a>

with a <directive module="core">ServerName</directive> matching that of

the base server. New domains on the same interface and port, but

requiring separate configurations, can then be added as subsequent (non-default)

virtual hosts.</p>

</note>

<note><title>ServerName inheritance</title>

<p> It is best to always explicitly list a <directive module="core"

>ServerName</directive> in every name-based virtual host.</p>

<p>If a <directive module="core">VirtualHost</directive> doesn't specify

a <directive module="core">ServerName</directive>, a server name will be

inherited from the base server configuration. If no server name was

specified globally, one is detected at startup through reverse DNS resolution

of the first listening address. In either case, this inherited server name

will influence name-based virtual host resolution, so it is best to always

explicitly list a <directive module="core">ServerName</directive> in every

name-based virtual host.</p>

</note>

<p>For example, suppose that you are serving the domain

<code>www.example.com</code> and you wish to add the virtual host

<code>other.example.com</code>, which points at the same IP address.

Then you simply add the following to <code>httpd.conf</code>:</p>

<highlight language="config">

&lt;VirtualHost *:80&gt;

# This first-listed virtual host is also the default for *:80

ServerName www.example.com

ServerAlias example.com

DocumentRoot "/www/domain"

&lt;/VirtualHost&gt;

&lt;VirtualHost *:80&gt;

ServerName other.example.com

DocumentRoot "/www/otherdomain"

&lt;/VirtualHost&gt;

</highlight>

<p>You can alternatively specify an explicit IP address in place of the

<code>*</code> in <directive type="section" module="core"

>VirtualHost</directive> directives. For example, you might want to do this

in order to run some name-based virtual hosts on one IP address, and either

IP-based, or another set of name-based virtual hosts on another address.</p>

<p>Many servers want to be accessible by more than one name. This is

possible with the <directive module="core">ServerAlias</directive>

directive, placed inside the <directive type="section" module="core"

>VirtualHost</directive> section. For example in the first <directive

type="section" module="core">VirtualHost</directive> block above, the

<directive module="core">ServerAlias</directive> directive indicates that

the listed names are other names which people can use to see that same

web site:</p>

<highlight language="config">

ServerAlias example.com *.example.com

</highlight>

<p>then requests for all hosts in the <code>example.com</code> domain will

be served by the <code>www.example.com</code> virtual host. The wildcard

characters <code>*</code> and <code>?</code> can be used to match names.

Of course, you can't just make up names and place them in <directive

module="core">ServerName</directive> or <code>ServerAlias</code>. You must

first have your DNS server properly configured to map those names to an IP

address associated with your server.</p>

<p>Name-based virtual hosts for the best-matching set of <directive

type="section" module="core">virtualhost</directive>s are processed

in the order they appear in the configuration. The first matching <directive

module="core">ServerName</directive> or <directive module="core"

>ServerAlias</directive> is used, with no different precedence for wildcards

(nor for ServerName vs. ServerAlias). </p>

<p>The complete list of names in the <directive module="core"

>VirtualHost</directive>

directive are treated just like a (non wildcard)

<directive module="core">ServerAlias</directive>.</p>

<p>Finally, you can fine-tune the configuration of the virtual hosts

by placing other directives inside the <directive type="section"

module="core">VirtualHost</directive> 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 <a href="/mod/directive-dict.html#Context">Context</a> of the

directive. Configuration directives set in the <em>main server context</em>

(outside any <directive type="section" module="core">VirtualHost</directive>

container) will be used only if they are not overridden by the virtual host

settings.</p>

</section>

</manualpage>