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

<title>Apache IP-based Virtual Host Support</title>

<seealso>

<a href="name-based.html">Name-based Virtual Hosts Support</a>

</seealso>

<section id="requirements"><title>System requirements</title>

<p>As the term <cite>IP-based</cite> indicates, the server

<strong>must have a different IP address for each IP-based

virtual host</strong>. This can be achieved by the machine

having several physical network connections, or by use of

virtual interfaces which are supported by most modern operating

systems (see system documentation for details, these are

frequently called "ip aliases", and the "ifconfig" command is

most commonly used to set them up).</p>

</section>

<section id="howto"><title>How to set up Apache</title>

<p>There are two ways of configuring apache to support multiple

hosts. Either by running a separate <program>httpd</program> daemon for

each hostname, or by running a single daemon which supports all the

virtual hosts.</p>

<p>Use multiple daemons when:</p>

<ul>

<li>There are security partitioning issues, such as company1

does not want anyone at company2 to be able to read their

data except via the web. In this case you would need two

daemons, each running with different <directive

module="mpm_common">User</directive>, <directive

module="mpm_common">Group</directive>, <directive

module="mpm_common">Listen</directive>, and <directive

module="core">ServerRoot</directive> settings.</li>

<li>You can afford the memory and file descriptor

requirements of listening to every IP alias on the

machine. It's only possible to <directive

module="mpm_common">Listen</directive> to the "wildcard"

address, or to specific addresses. So if you have a need to

listen to a specific address for whatever reason, then you

will need to listen to all specific addresses. (Although one

<program>httpd</program> could listen to N-1 of the addresses, and another could

listen to the remaining address.)</li>

</ul>

<p>Use a single daemon when:</p>

<ul>

<li>Sharing of the httpd configuration between virtual hosts

is acceptable.</li>

<li>The machine services a large number of requests, and so

the performance loss in running separate daemons may be

significant.</li>

</ul>

</section>

<section id="multiple"><title>Setting up multiple daemons</title>

<p>Create a separate <program>httpd</program> installation for each

virtual host. For each installation, use the <directive

module="mpm_common">Listen</directive> directive in the

configuration file to select which IP address (or virtual host)

that daemon services. e.g.</p>

<example>

Listen www.smallco.com:80

</example>

<p>It is recommended that you use an IP address instead of a

hostname (see <a href="/dns-caveats.html">DNS caveats</a>).</p>

</section>

<section id="single"><title>Setting up a single daemon

with virtual hosts</title>

<p>For this case, a single <program>httpd</program> will service

requests for the main server and all the virtual hosts. The <directive

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

in the configuration file is used to set the values of <directive

module="core">ServerAdmin</directive>, <directive

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

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

module="core">ErrorLog</directive> and <directive

module="mod_log_config">TransferLog</directive>

or <directive module="mod_log_config">CustomLog</directive>

configuration directives to different values for each virtual

host. e.g.</p>

<example>

&lt;VirtualHost www.smallco.com&gt;<br />

ServerAdmin webmaster@mail.smallco.com<br />

DocumentRoot /groups/smallco/www<br />

ServerName www.smallco.com<br />

ErrorLog /groups/smallco/logs/error_log<br />

TransferLog /groups/smallco/logs/access_log<br />

&lt;/VirtualHost&gt;<br />

<br />

&lt;VirtualHost www.baygroup.org&gt;<br />

ServerAdmin webmaster@mail.baygroup.org<br />

DocumentRoot /groups/baygroup/www<br />

ServerName www.baygroup.org<br />

ErrorLog /groups/baygroup/logs/error_log<br />

TransferLog /groups/baygroup/logs/access_log<br />

&lt;/VirtualHost&gt;

</example>

<p>It is recommended that you use an IP address instead of a

hostname (see <a href="/dns-caveats.html">DNS caveats</a>).</p>

<p>Almost <strong>any</strong> configuration directive can be

put in the VirtualHost directive, with the exception of

directives that control process creation and a few other

directives. To find out if a directive can be used in the

VirtualHost directive, check the <a

href="/mod/directive-dict.html#Context">Context</a> using the

<a href="/mod/directives.html">directive index</a>.</p>

<p><directive module="mod_suexec">SuexecUserGroup</directive>

may be used inside a

VirtualHost directive if the <a href="/suexec.html">suEXEC

wrapper</a> is used.</p>

<p><em>SECURITY:</em> When specifying where to write log files,

be aware of some security risks which are present if anyone

other than the user that starts Apache has write access to the

directory where they are written. See the <a

href="/misc/security_tips.html">security tips</a> document

for details.</p>

</section>

</manualpage>