APACHE_1_3_42/htdocs/manual/vhosts/virtual-host.html - httpd - Git at Google

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     <title>Apache Server Virtual Host Support</title>
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     <h1 align="CENTER">Virtual Host Support</h1>
     <strong>See Also:</strong> <a href="host.html">Non-IP based
     virtual hosts</a>

     <h2>What are virtual hosts?</h2>
     This is the ability of a single machine to be a web server for
     multiple domains. For example, an Internet service provider
     might have a machine called <code>www.serve.com</code> which
     provides Web space for several organizations including, say,
     <em>smallco</em> and <em>baygroup</em>. Ordinarily, these
     groups would be given parts of the Web tree on www.serve.com.
     So smallco's home page would have the URL

     <blockquote>
       http://www.serve.com/smallco/
     </blockquote>
     and baygroup's home page would have the URL

     <blockquote>
       http://www.serve.com/baygroup/
     </blockquote>

     <p>For esthetic reasons, however, both organizations would
     rather their home pages appeared under their own names rather
     than that of the service provider's; but they do not want to
     set up their own Internet links and servers.</p>

     <p>Virtual hosts are the solution to this problem. smallco and
     baygroup would have their own Internet name registrations,
     <code>www.smallco.com</code> and <code>www.baygroup.org</code>
     respectively. These hostnames would both correspond to the
     service provider's machine (www.serve.com). Thus smallco's home
     page would now have the URL</p>

     <blockquote>
       http://www.smallco.com/
     </blockquote>
     and baygroup's home page would have the URL

     <blockquote>
       http://www.baygroup.org/
     </blockquote>

     <h2>System requirements</h2>
     Due to limitations in the HTTP/1.0 protocol, the web server
     <strong>must have a different IP address for each virtual
     host</strong>. This can be achieved by the machine having
     several physical network connections, or by use of a <a
     href="../misc/vif-info.html">virtual interface</a> on some
     operating systems.

     <h2>How to set up Apache</h2>
     There are two ways of configuring apache to support multiple
     hosts. Either by running a separate httpd daemon for each
     hostname, or by running a single daemon which supports all the
     virtual hosts.

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

     <ul>
       <li>The different virtual hosts need very different httpd
       configurations, such as different values for: <a
       href="../mod/core.html#servertype">ServerType</a>, <a
       href="../mod/core.html#user">User</a>, <a
       href="../mod/core.html#group">Group</a>, <a
       href="../mod/mod_mime.html#typesconfig">TypesConfig</a> or <a
       href="../mod/core.html#serverroot">ServerRoot</a>.</li>

       <li>The machine does not process a very high request
       rate.</li>
     </ul>
     Use a single daemon when:

     <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>

     <h2>Setting up multiple daemons</h2>
     Create a separate httpd installation for each virtual host. For
     each installation, use the <a
     href="../mod/core.html#bindaddress">BindAddress</a> directive
     in the configuration file to select which IP address (or
     virtual host) that daemon services. <em>E.g.</em>,

     <blockquote>
       <code>BindAddress www.smallco.com</code>
     </blockquote>
     This hostname can also be given as an IP address.

     <h2>Setting up a single daemon</h2>
     For this case, a single httpd will service requests for all the
     virtual hosts. The <a
     href="../mod/core.html#virtualhost">VirtualHost</a> directive
     in the configuration file is used to set the values of <a
     href="../mod/core.html#serveradmin">ServerAdmin</a>, <a
     href="../mod/core.html#servername">ServerName</a>, <a
     href="../mod/core.html#documentroot">DocumentRoot</a>, <a
     href="../mod/core.html#errorlog">ErrorLog</a> and <a
     href="../mod/mod_log_config.html#transferlog">TransferLog</a>
     configuration directives to different values for each virtual
     host. <em>E.g.</em>,

     <blockquote>
       <code>&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;<br />
       </code>
     </blockquote>
     This VirtualHost hostnames can also be given as IP addresses.

     <p>Almost <strong>ANY</strong> configuration directive can be
     put in the VirtualHost directive, with the exception of <a
     href="../mod/core.html#servertype">ServerType</a>, <a
     href="../mod/core.html#user">User</a>, <a
     href="../mod/core.html#group">Group</a>, <a
     href="../mod/core.html#startservers">StartServers</a>, <a
     href="../mod/core.html#maxspareservers">MaxSpareServers</a>, <a
     href="../mod/core.html#minspareservers">MinSpareServers</a>, <a
     href="../mod/core.html#maxrequestsperchild">MaxRequestsPerChild</a>,
     <a href="../mod/core.html#bindaddress">BindAddress</a>, <a
     href="../mod/core.html#pidfile">PidFile</a>, <a
     href="../mod/mod_mime.html#typesconfig">TypesConfig</a>, and <a
     href="../mod/core.html#serverroot">ServerRoot</a>.</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>

     <h2>File Handle/Resource Limits:</h2>
     When using a large number of Virtual Hosts, Apache may run out
     of available file descriptors if each Virtual Host specifies
     different log files. The total number of file descriptors used
     by Apache is one for each distinct error log file, one for
     every other log file directive, plus 10-20 for internal use.
     Unix operating systems limit the number of file descriptors
     that may be used by a process; the limit is typically 64, and
     may usually be increased up to a large hard-limit.

     <p>Although Apache attempts to increase the limit as required,
     this may not work if:</p>

     <ol>
       <li>Your system does not provide the setrlimit() system
       call.</li>

       <li>The setrlimit(RLIMIT_NOFILE) call does not function on
       your system (such as Solaris 2.3)</li>

       <li>The number of file descriptors required exceeds the hard
       limit.</li>

       <li>Your system imposes other limits on file descriptors,
       such as a limit on stdio streams only using file descriptors
       below 256. (Solaris 2)</li>
     </ol>
     In the event of problems you can:

     <ul>
       <li>Reduce the number of log files; don't specify log files
       in the VirtualHost sections, but only log to the main log
       files.</li>

       <li>
         If you system falls into 1 or 2 (above), then increase the
         file descriptor limit before starting Apache, using a
         script like

         <blockquote>
           <code>#!/bin/sh<br />
            ulimit -S -n 100<br />
            exec httpd</code>
         </blockquote>
       </li>
     </ul>
     The have been reports that Apache may start running out of
     resources allocated for the root process. This will exhibit
     itself as errors in the error log like "unable to fork". There
     are two ways you can bump this up:

     <ol>
       <li>Have a <code>csh</code> script wrapper around httpd which
       sets the "rlimit" to some large number, like 512.</li>

       <li>
         Edit http_main.c to add calls to setrlimit() from main(),
         along the lines of
 <pre>
         struct rlimit rlp;

         rlp.rlim_cur = rlp.rlim_max = 512;
         if (setrlimit(RLIMIT_NPROC, &amp;rlp)) {
             fprintf(stderr, "setrlimit(RLIMIT_NPROC) failed.\n");
             exit(1);
         }
 </pre>
         (thanks to "Aaron Gifford &lt;agifford@InfoWest.COM&gt;"
         for the patch)
       </li>
     </ol>
     The latter will probably manifest itself in a later version of
     Apache. <!--#include virtual="footer.html" -->
   </body>
 </html>
	<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
	"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

	<html xmlns="http://www.w3.org/1999/xhtml">
	<head>
	<meta name="generator" content="HTML Tidy, see www.w3.org" />

	<title>Apache Server Virtual Host Support</title>
	</head>
	<!-- Background white, links blue (unvisited), navy (visited), red (active) -->

	<body bgcolor="#FFFFFF" text="#000000" link="#0000FF"
	vlink="#000080" alink="#FF0000">
	<!--#include virtual="header.html" -->

	<h1 align="CENTER">Virtual Host Support</h1>
	<strong>See Also:</strong> <a href="host.html">Non-IP based
	virtual hosts</a>

	<h2>What are virtual hosts?</h2>
	This is the ability of a single machine to be a web server for
	multiple domains. For example, an Internet service provider
	might have a machine called <code>www.serve.com</code> which
	provides Web space for several organizations including, say,
	<em>smallco</em> and <em>baygroup</em>. Ordinarily, these
	groups would be given parts of the Web tree on www.serve.com.
	So smallco's home page would have the URL

	<blockquote>
	http://www.serve.com/smallco/
	</blockquote>
	and baygroup's home page would have the URL

	<blockquote>
	http://www.serve.com/baygroup/
	</blockquote>

	<p>For esthetic reasons, however, both organizations would
	rather their home pages appeared under their own names rather
	than that of the service provider's; but they do not want to
	set up their own Internet links and servers.</p>

	<p>Virtual hosts are the solution to this problem. smallco and
	baygroup would have their own Internet name registrations,
	<code>www.smallco.com</code> and <code>www.baygroup.org</code>
	respectively. These hostnames would both correspond to the
	service provider's machine (www.serve.com). Thus smallco's home
	page would now have the URL</p>

	<blockquote>
	http://www.smallco.com/
	</blockquote>
	and baygroup's home page would have the URL

	<blockquote>
	http://www.baygroup.org/
	</blockquote>

	<h2>System requirements</h2>
	Due to limitations in the HTTP/1.0 protocol, the web server
	<strong>must have a different IP address for each virtual
	host</strong>. This can be achieved by the machine having
	several physical network connections, or by use of a <a
	href="../misc/vif-info.html">virtual interface</a> on some
	operating systems.

	<h2>How to set up Apache</h2>
	There are two ways of configuring apache to support multiple
	hosts. Either by running a separate httpd daemon for each
	hostname, or by running a single daemon which supports all the
	virtual hosts.

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

	<ul>
	<li>The different virtual hosts need very different httpd
	configurations, such as different values for: <a
	href="../mod/core.html#servertype">ServerType</a>, <a
	href="../mod/core.html#user">User</a>, <a
	href="../mod/core.html#group">Group</a>, <a
	href="../mod/mod_mime.html#typesconfig">TypesConfig</a> or <a
	href="../mod/core.html#serverroot">ServerRoot</a>.</li>

	<li>The machine does not process a very high request
	rate.</li>
	</ul>
	Use a single daemon when:

	<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>

	<h2>Setting up multiple daemons</h2>
	Create a separate httpd installation for each virtual host. For
	each installation, use the <a
	href="../mod/core.html#bindaddress">BindAddress</a> directive
	in the configuration file to select which IP address (or
	virtual host) that daemon services. <em>E.g.</em>,

	<blockquote>
	<code>BindAddress www.smallco.com</code>
	</blockquote>
	This hostname can also be given as an IP address.

	<h2>Setting up a single daemon</h2>
	For this case, a single httpd will service requests for all the
	virtual hosts. The <a
	href="../mod/core.html#virtualhost">VirtualHost</a> directive
	in the configuration file is used to set the values of <a
	href="../mod/core.html#serveradmin">ServerAdmin</a>, <a
	href="../mod/core.html#servername">ServerName</a>, <a
	href="../mod/core.html#documentroot">DocumentRoot</a>, <a
	href="../mod/core.html#errorlog">ErrorLog</a> and <a
	href="../mod/mod_log_config.html#transferlog">TransferLog</a>
	configuration directives to different values for each virtual
	host. <em>E.g.</em>,

	<blockquote>
	<code><VirtualHost www.smallco.com><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 />
	</VirtualHost><br />
	<br />
	<VirtualHost www.baygroup.org><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 />
	</VirtualHost><br />
	</code>
	</blockquote>
	This VirtualHost hostnames can also be given as IP addresses.

	<p>Almost <strong>ANY</strong> configuration directive can be
	put in the VirtualHost directive, with the exception of <a
	href="../mod/core.html#servertype">ServerType</a>, <a
	href="../mod/core.html#user">User</a>, <a
	href="../mod/core.html#group">Group</a>, <a
	href="../mod/core.html#startservers">StartServers</a>, <a
	href="../mod/core.html#maxspareservers">MaxSpareServers</a>, <a
	href="../mod/core.html#minspareservers">MinSpareServers</a>, <a
	href="../mod/core.html#maxrequestsperchild">MaxRequestsPerChild</a>,
	<a href="../mod/core.html#bindaddress">BindAddress</a>, <a
	href="../mod/core.html#pidfile">PidFile</a>, <a
	href="../mod/mod_mime.html#typesconfig">TypesConfig</a>, and <a
	href="../mod/core.html#serverroot">ServerRoot</a>.</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>

	<h2>File Handle/Resource Limits:</h2>
	When using a large number of Virtual Hosts, Apache may run out
	of available file descriptors if each Virtual Host specifies
	different log files. The total number of file descriptors used
	by Apache is one for each distinct error log file, one for
	every other log file directive, plus 10-20 for internal use.
	Unix operating systems limit the number of file descriptors
	that may be used by a process; the limit is typically 64, and
	may usually be increased up to a large hard-limit.

	<p>Although Apache attempts to increase the limit as required,
	this may not work if:</p>

	<ol>
	<li>Your system does not provide the setrlimit() system
	call.</li>

	<li>The setrlimit(RLIMIT_NOFILE) call does not function on
	your system (such as Solaris 2.3)</li>

	<li>The number of file descriptors required exceeds the hard
	limit.</li>

	<li>Your system imposes other limits on file descriptors,
	such as a limit on stdio streams only using file descriptors
	below 256. (Solaris 2)</li>
	</ol>
	In the event of problems you can:

	<ul>
	<li>Reduce the number of log files; don't specify log files
	in the VirtualHost sections, but only log to the main log
	files.</li>

	<li>
	If you system falls into 1 or 2 (above), then increase the
	file descriptor limit before starting Apache, using a
	script like

	<blockquote>
	<code>#!/bin/sh<br />
	ulimit -S -n 100<br />
	exec httpd</code>
	</blockquote>
	</li>
	</ul>
	The have been reports that Apache may start running out of
	resources allocated for the root process. This will exhibit
	itself as errors in the error log like "unable to fork". There
	are two ways you can bump this up:

	<ol>
	<li>Have a <code>csh</code> script wrapper around httpd which
	sets the "rlimit" to some large number, like 512.</li>

	<li>
	Edit http_main.c to add calls to setrlimit() from main(),
	along the lines of
	<pre>
	struct rlimit rlp;

	rlp.rlim_cur = rlp.rlim_max = 512;
	if (setrlimit(RLIMIT_NPROC, &rlp)) {
	fprintf(stderr, "setrlimit(RLIMIT_NPROC) failed.\n");
	exit(1);
	}
	</pre>
	(thanks to "Aaron Gifford <agifford@InfoWest.COM>"
	for the patch)
	</li>
	</ol>
	The latter will probably manifest itself in a later version of
	Apache. <!--#include virtual="footer.html" -->
	</body>
	</html>