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| <manualpage metafile="mass.xml.meta"> |
| <parentdocument href="./">Virtual Hosts</parentdocument> |
| <title>Dynamically Configured Mass Virtual Hosting</title> |
| |
| <summary> |
| |
| <p>This document describes how to efficiently serve an |
| arbitrary number of virtual hosts with the Apache HTTP Server. A |
| <a href="../rewrite/vhosts.html">separate document</a> discusses using |
| <module>mod_rewrite</module> to create dynamic mass virtual hosts. |
| </p> |
| |
| </summary> |
| |
| <section id="motivation"><title>Motivation</title> |
| |
| <p>The techniques described here are of interest if your |
| <code>httpd.conf</code> contains many |
| <code><VirtualHost></code> sections that are |
| substantially the same, for example:</p> |
| |
| <highlight language="config"> |
| <VirtualHost 111.22.33.44> |
| ServerName customer-1.example.com |
| DocumentRoot "/www/hosts/customer-1.example.com/docs" |
| ScriptAlias "/cgi-bin/" "/www/hosts/customer-1.example.com/cgi-bin" |
| </VirtualHost> |
| |
| <VirtualHost 111.22.33.44> |
| ServerName customer-2.example.com |
| DocumentRoot "/www/hosts/customer-2.example.com/docs" |
| ScriptAlias "/cgi-bin/" "/www/hosts/customer-2.example.com/cgi-bin" |
| </VirtualHost> |
| |
| <VirtualHost 111.22.33.44> |
| ServerName customer-N.example.com |
| DocumentRoot "/www/hosts/customer-N.example.com/docs" |
| ScriptAlias "/cgi-bin/" "/www/hosts/customer-N.example.com/cgi-bin" |
| </VirtualHost> |
| </highlight> |
| |
| <p>We wish to replace these multiple |
| <code><VirtualHost></code> blocks with a mechanism |
| that works them out dynamically. This has a number of |
| advantages:</p> |
| |
| <ol> |
| <li>Your configuration file is smaller, so Apache starts |
| more quickly and uses less memory. Perhaps more importantly, the |
| smaller configuration is easier to maintain, and leaves less room |
| for errors.</li> |
| |
| <li>Adding virtual hosts is simply a matter of creating the |
| appropriate directories in the filesystem and entries in the |
| DNS - you don't need to reconfigure or restart Apache.</li> |
| </ol> |
| |
| <p>The main disadvantage is that you cannot have a different log file for |
| each virtual host; however, if you have many virtual hosts, doing |
| this can be a bad idea anyway, because of the <a |
| href="fd-limits.html">number of file descriptors needed</a>. |
| It is better to <a href="../logs.html#piped">log to a pipe or a fifo</a>, |
| and arrange for the process at the other end to split up the log |
| files into one per virtual host. One example of such a process can |
| be found in the <a |
| href="../programs/split-logfile.html">split-logfile</a> |
| utility.</p> |
| |
| </section> |
| |
| <section id="overview"><title>Overview</title> |
| |
| <p>A virtual host is defined by two pieces of information: its |
| IP address, and the contents of the <code>Host:</code> header |
| in the HTTP request. The dynamic mass virtual hosting technique |
| used here is based on automatically inserting this information into the |
| pathname of the file that is used to satisfy the request. This |
| can be most easily done by using <module>mod_vhost_alias</module> |
| with Apache httpd. Alternatively, |
| <a href="../rewrite/vhosts.html">mod_rewrite can |
| be used</a>.</p> |
| <p>Both of these modules are disabled by default; you must enable |
| one of them when configuring and building Apache httpd if you want to |
| use this technique.</p> |
| |
| <p>A couple of things need to be determined from the request in |
| order to make the dynamic |
| virtual host look like a normal one. The most important is the |
| server name, which is used by the server to generate |
| self-referential URLs etc. It is configured with the |
| <code>ServerName</code> directive, and it is available to CGIs |
| via the <code>SERVER_NAME</code> environment variable. The |
| actual value used at run time is controlled by the <directive |
| module="core">UseCanonicalName</directive> |
| setting. With <code>UseCanonicalName Off</code>, the server name |
| is taken from the contents of the <code>Host:</code> header in the |
| request. With <code>UseCanonicalName DNS</code>, it is taken from a |
| reverse DNS lookup of the virtual host's IP address. The former |
| setting is used for name-based dynamic virtual hosting, and the |
| latter is used for IP-based hosting. If httpd cannot work out |
| the server name because there is no <code>Host:</code> header, |
| or the DNS lookup fails, then the value configured with |
| <code>ServerName</code> is used instead.</p> |
| |
| <p>The other thing to determine is the document root (configured |
| with <code>DocumentRoot</code> and available to CGI scripts via the |
| <code>DOCUMENT_ROOT</code> environment variable). In a normal |
| configuration, this is used by the core module when |
| mapping URIs to filenames, but when the server is configured to |
| do dynamic virtual hosting, that job must be taken over by another |
| module (either <module>mod_vhost_alias</module> or |
| <module>mod_rewrite</module>), which has a different way of doing |
| the mapping. Neither of these modules is responsible for |
| setting the <code>DOCUMENT_ROOT</code> environment variable so |
| if any CGIs or SSI documents make use of it, they will get a |
| misleading value.</p> |
| |
| </section> |
| |
| <section id="simple"><title>Dynamic Virtual Hosts with |
| mod_vhost_alias</title> |
| |
| <p>This extract from <code>httpd.conf</code> implements the |
| virtual host arrangement outlined in the <a |
| href="#motivation">Motivation</a> section above |
| using <module>mod_vhost_alias</module>.</p> |
| |
| <highlight language="config"> |
| # get the server name from the Host: header |
| UseCanonicalName Off |
| |
| # this log format can be split per-virtual-host based on the first field |
| # using the split-logfile utility. |
| LogFormat "%V %h %l %u %t \"%r\" %s %b" vcommon |
| CustomLog "logs/access_log" vcommon |
| |
| # include the server name in the filenames used to satisfy requests |
| VirtualDocumentRoot "/www/hosts/%0/docs" |
| VirtualScriptAlias "/www/hosts/%0/cgi-bin" |
| </highlight> |
| |
| <p>This configuration can be changed into an IP-based virtual |
| hosting solution by just turning <code>UseCanonicalName |
| Off</code> into <code>UseCanonicalName DNS</code>. The server |
| name that is inserted into the filename is then derived from |
| the IP address of the virtual host. The variable <code>%0</code> |
| references the requested servername, as indicated in the |
| <code>Host:</code> header.</p> |
| |
| <p>See the <module>mod_vhost_alias</module> documentation for more usage |
| examples.</p> |
| |
| </section> |
| |
| <section id="homepages"><title>Simplified Dynamic Virtual Hosts</title> |
| |
| <p>This is an adjustment of the above system, tailored for an |
| ISP's web hosting server. Using <code>%2</code>, |
| we can select substrings of the server name to |
| use in the filename so that, for example, the documents for |
| <code>www.user.example.com</code> are found in |
| <code>/home/user/www</code>. It uses a single <code>cgi-bin</code> |
| directory instead of one per virtual host.</p> |
| |
| <highlight language="config"> |
| UseCanonicalName Off |
| |
| LogFormat "%V %h %l %u %t \"%r\" %s %b" vcommon |
| CustomLog "logs/access_log" vcommon |
| |
| # include part of the server name in the filenames |
| VirtualDocumentRoot "/home/%2/www" |
| |
| # single cgi-bin directory |
| ScriptAlias "/cgi-bin/" "/www/std-cgi/" |
| </highlight> |
| |
| <p>There are examples of more complicated |
| <code>VirtualDocumentRoot</code> settings in the |
| <module>mod_vhost_alias</module> documentation.</p> |
| |
| </section> |
| |
| <section id="combinations"><title>Using Multiple Virtual |
| Hosting Systems on the Same Server</title> |
| |
| <p>With more complicated setups, you can use httpd's normal |
| <code><VirtualHost></code> directives to control the |
| scope of the various virtual hosting configurations. For |
| example, you could have one IP address for general customers' homepages, |
| and another for commercial customers, with the following setup. |
| This can be combined with conventional |
| <code><VirtualHost></code> configuration sections, as shown |
| below.</p> |
| |
| <highlight language="config"> |
| UseCanonicalName Off |
| |
| LogFormat "%V %h %l %u %t \"%r\" %s %b" vcommon |
| |
| <Directory "/www/commercial"> |
| Options FollowSymLinks |
| AllowOverride All |
| </Directory> |
| |
| <Directory "/www/homepages"> |
| Options FollowSymLinks |
| AllowOverride None |
| </Directory> |
| |
| <VirtualHost 111.22.33.44> |
| ServerName www.commercial.example.com |
| |
| CustomLog "logs/access_log.commercial" vcommon |
| |
| VirtualDocumentRoot "/www/commercial/%0/docs" |
| VirtualScriptAlias "/www/commercial/%0/cgi-bin" |
| </VirtualHost> |
| |
| <VirtualHost 111.22.33.45> |
| ServerName www.homepages.example.com |
| |
| CustomLog "logs/access_log.homepages" vcommon |
| |
| VirtualDocumentRoot "/www/homepages/%0/docs" |
| ScriptAlias "/cgi-bin/" "/www/std-cgi/" |
| </VirtualHost> |
| </highlight> |
| |
| <note> |
| <title>Note</title> |
| <p>If the first VirtualHost block does <em>not</em> include a |
| <directive module="core">ServerName</directive> directive, the reverse |
| DNS of the relevant IP will be used instead. |
| If this is not the server name you |
| wish to use, a bogus entry (eg. <code>ServerName |
| none.example.com</code>) can be added to get around this |
| behaviour.</p> |
| </note> |
| |
| </section> |
| |
| <section id="ipbased"><title>More Efficient IP-Based Virtual Hosting</title> |
| |
| <p>The configuration changes suggested to turn <a href="#simple">the first |
| example</a> into an IP-based virtual hosting setup result in |
| a rather inefficient setup. A new DNS lookup is required for every |
| request. To avoid this overhead, the filesystem can be arranged to |
| correspond to the IP addresses, instead of to the host names, thereby |
| negating the need for a DNS lookup. Logging will also have to be adjusted |
| to fit this system.</p> |
| |
| <highlight language="config"> |
| # get the server name from the reverse DNS of the IP address |
| UseCanonicalName DNS |
| |
| # include the IP address in the logs so they may be split |
| LogFormat "%A %h %l %u %t \"%r\" %s %b" vcommon |
| CustomLog "logs/access_log" vcommon |
| |
| # include the IP address in the filenames |
| VirtualDocumentRootIP "/www/hosts/%0/docs" |
| VirtualScriptAliasIP "/www/hosts/%0/cgi-bin" |
| </highlight> |
| |
| </section> |
| |
| <section id="rewrite"><title>Mass virtual hosts with |
| mod_rewrite</title> |
| |
| <p> |
| Mass virtual hosting may also be accomplished using |
| <module>mod_rewrite</module>, either using simple <directive |
| module="mod_rewrite">RewriteRule</directive> directives, or using more |
| complicated techniques such as storing the vhost definitions externally |
| and accessing them via <directive |
| module="mod_rewrite">RewriteMap</directive>. These techniques are |
| discussed in the <a href="../rewrite/vhosts.html">rewrite |
| documentation</a>.</p> |
| </section> |
| |
| <section id="macro"><title>Mass virtual hosts with mod_macro</title> |
| |
| <p>Another option for dynamically generated virtual hosts is |
| <module>mod_macro</module>, with which you can create a virtualhost |
| template, and invoke it for multiple hostnames. An example of this is |
| provided in the <strong>Usage</strong> section of the module |
| documentation. |
| </p> |
| </section> |
| |
| </manualpage> |