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| <title>Dynamically configured mass virtual hosting</title> |
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| <h1 align="CENTER">Dynamically configured mass virtual |
| hosting</h1> |
| |
| <p>This document describes how to efficiently serve an |
| arbitrary number of virtual hosts with Apache 1.3. <!-- |
| |
| Written by Tony Finch (fanf@demon.net) (dot@dotat.at). |
| |
| Some examples were derived from Ralf S. Engleschall's document |
| http://www.engelschall.com/pw/apache/rewriteguide/ |
| |
| Some suggestions were made by Brian Behlendorf. |
| |
| --> |
| </p> |
| |
| <h2><a id="contents" name="contents">Contents:</a></h2> |
| |
| <ul> |
| <li><a href="#motivation">Motivation</a></li> |
| |
| <li><a href="#overview">Overview</a></li> |
| |
| <li><a href="#simple">Simple dynamic virtual hosts</a></li> |
| |
| <li><a href="#homepages">A virtually hosted homepages |
| system</a></li> |
| |
| <li><a href="#combinations">Using more than one virtual |
| hosting system on the same server</a></li> |
| |
| <li><a href="#ipbased">More efficient IP-based virtual |
| hosting</a></li> |
| |
| <li><a href="#oldversion">Using older versions of |
| Apache</a></li> |
| |
| <li><a href="#simple.rewrite">Simple dynamic virtual hosts |
| using <code>mod_rewrite</code></a></li> |
| |
| <li><a href="#homepages.rewrite">A homepages system using |
| <code>mod_rewrite</code></a></li> |
| |
| <li><a href="#xtra-conf">Using a separate virtual host |
| configuration file</a></li> |
| </ul> |
| <hr /> |
| |
| <h2><a id="motivation" name="motivation">Motivation</a></h2> |
| |
| <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> |
| <pre> |
| NameVirtualHost 111.22.33.44 |
| <VirtualHost 111.22.33.44> |
| ServerName www.customer-1.com |
| DocumentRoot /www/hosts/www.customer-1.com/docs |
| ScriptAlias /cgi-bin/ /www/hosts/www.customer-1.com/cgi-bin |
| </VirtualHost> |
| <VirtualHost 111.22.33.44> |
| ServerName www.customer-2.com |
| DocumentRoot /www/hosts/www.customer-2.com/docs |
| ScriptAlias /cgi-bin/ /www/hosts/www.customer-2.com/cgi-bin |
| </VirtualHost> |
| # blah blah blah |
| <VirtualHost 111.22.33.44> |
| ServerName www.customer-N.com |
| DocumentRoot /www/hosts/www.customer-N.com/docs |
| ScriptAlias /cgi-bin/ /www/hosts/www.customer-N.com/cgi-bin |
| </VirtualHost> |
| </pre> |
| <br /> |
| <br /> |
| |
| |
| <p>The basic idea is to replace all of the static |
| <code><VirtualHost></code> configuration with a mechanism |
| that works it out dynamically. This has a number of |
| advantages:</p> |
| |
| <ol> |
| <li>Your configuration file is smaller so Apache starts |
| faster and uses less memory.</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> |
| <br /> |
| <br /> |
| |
| |
| <p>The main disadvantage is that you cannot have a different |
| log file for each virtual host; however if you have very many |
| virtual hosts then doing this is dubious anyway because it eats |
| file descriptors. It is better to log to a pipe or a fifo and |
| arrange for the process at the other end to distribute the logs |
| to the customers (it can also accumulate statistics, etc.).</p> |
| <hr /> |
| |
| <h2><a id="overview" name="overview">Overview</a></h2> |
| |
| <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 |
| is based on automatically inserting this information into the |
| pathname of the file that is used to satisfy the request. This |
| is done most easily using <a |
| href="../mod/mod_vhost_alias.html"><code>mod_vhost_alias</code></a>, |
| but if you are using a version of Apache up to 1.3.6 then you |
| must use <a |
| href="../mod/mod_rewrite.html"><code>mod_rewrite</code></a>. |
| Both of these modules are disabled by default; you must enable |
| one of them when configuring and building Apache if you want to |
| use this technique.</p> |
| |
| <p>A couple of things need to be `faked' to make the dynamic |
| virtual host look like a normal one. The most important is the |
| server name which is used by Apache 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 <a |
| href="../mod/core.html#usecanonicalname"><code>UseCanonicalName</code></a> |
| setting. With <code>UseCanonicalName Off</code> the server name |
| comes from the contents of the <code>Host:</code> header in the |
| request. With <code>UseCanonicalName DNS</code> it comes 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 Apache 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 `fake' is the document root (configured |
| with <code>DocumentRoot</code> and available to CGIs via the |
| <code>DOCUMENT_ROOT</code> environment variable). In a normal |
| configuration this setting is used by the core module when |
| mapping URIs to filenames, but when the server is configured to |
| do dynamic virtual hosting that job is taken over by another |
| module (either <code>mod_vhost_alias</code> or |
| <code>mod_rewrite</code>) 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> |
| <hr /> |
| |
| <h2><a id="simple" name="simple">Simple dynamic virtual |
| hosts</a></h2> |
| |
| <p>This extract from <code>httpd.conf</code> implements the |
| virtual host arrangement outlined in the <a |
| href="#motivation">Motivation</a> section above, but in a |
| generic fashion using <code>mod_vhost_alias</code>.</p> |
| <pre> |
| # get the server name from the Host: header |
| UseCanonicalName Off |
| |
| # this log format can be split per-virtual-host based on the first field |
| 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 |
| </pre> |
| |
| <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.</p> |
| <hr /> |
| |
| <h2><a id="homepages" name="homepages">A virtually hosted |
| homepages system</a></h2> |
| |
| <p>This is an adjustment of the above system tailored for an |
| ISP's homepages server. Using a slightly more complicated |
| configuration we can select substrings of the server name to |
| use in the filename so that e.g. the documents for |
| <samp>www.user.isp.com</samp> are found in |
| <code>/home/user/</code>. It uses a single <code>cgi-bin</code> |
| directory instead of one per virtual host.</p> |
| <pre> |
| # all the preliminary stuff is the same as above, then |
| |
| # include part of the server name in the filenames |
| VirtualDocumentRoot /www/hosts/%2/docs |
| |
| # single cgi-bin directory |
| ScriptAlias /cgi-bin/ /www/std-cgi/ |
| </pre> |
| |
| <p>There are examples of more complicated |
| <code>VirtualDocumentRoot</code> settings in <a |
| href="../mod/mod_vhost_alias.html">the |
| <code>mod_vhost_alias</code> documentation</a>.</p> |
| <hr /> |
| |
| <h2><a id="combinations" name="combinations">Using more than |
| one virtual hosting system on the same server</a></h2> |
| |
| <p>With more complicated setups you can use Apache'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 homepages customers |
| and another for commercial customers with the following setup. |
| This can of course be combined with conventional |
| <code><VirtualHost></code> configuration sections.</p> |
| <pre> |
| 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.isp.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.isp.com |
| |
| CustomLog logs/access_log.homepages vcommon |
| |
| VirtualDocumentRoot /www/homepages/%0/docs |
| ScriptAlias /cgi-bin/ /www/std-cgi/ |
| </VirtualHost> |
| </pre> |
| <hr /> |
| |
| <h2><a id="ipbased" name="ipbased">More efficient IP-based |
| virtual hosting</a></h2> |
| |
| <p>After <a href="#simple">the first example</a> I noted that |
| it is easy to turn it into an IP-based virtual hosting setup. |
| Unfortunately that configuration is not very efficient because |
| it requires a DNS lookup for every request. This can be avoided |
| by laying out the filesystem according to the IP addresses |
| themselves rather than the corresponding names and changing the |
| logging similarly. Apache will then usually not need to work |
| out the server name and so incur a DNS lookup.</p> |
| <pre> |
| # 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 |
| </pre> |
| <hr /> |
| |
| <h2><a id="oldversion" name="oldversion">Using older versions |
| of Apache</a></h2> |
| |
| <p>The examples above rely on <code>mod_vhost_alias</code> |
| which appeared after version 1.3.6. If you are using a version |
| of Apache without <code>mod_vhost_alias</code> then you can |
| implement this technique with <code>mod_rewrite</code> as |
| illustrated below, but only for Host:-header-based virtual |
| hosts.</p> |
| |
| <p>In addition there are some things to beware of with logging. |
| Apache 1.3.6 is the first version to include the |
| <code>%V</code> log format directive; in versions 1.3.0 - 1.3.3 |
| the <code>%v</code> option did what <code>%V</code> does; |
| version 1.3.4 has no equivalent. In all these versions of |
| Apache the <code>UseCanonicalName</code> directive can appear |
| in <code>.htaccess</code> files which means that customers can |
| cause the wrong thing to be logged. Therefore the best thing to |
| do is use the <code>%{Host}i</code> directive which logs the |
| <code>Host:</code> header directly; note that this may include |
| <code>:port</code> on the end which is not the case for |
| <code>%V</code>.</p> |
| <hr /> |
| |
| <h2><a id="simple.rewrite" name="simple.rewrite">Simple dynamic |
| virtual hosts using <code>mod_rewrite</code></a></h2> |
| |
| <p>This extract from <code>httpd.conf</code> does the same |
| thing as <a href="#simple">the first example</a>. The first |
| half is very similar to the corresponding part above but with |
| some changes for backward compatibility and to make the |
| <code>mod_rewrite</code> part work properly; the second half |
| configures <code>mod_rewrite</code> to do the actual work.</p> |
| |
| <p>There are a couple of especially tricky bits: By default, |
| <code>mod_rewrite</code> runs before the other URI translation |
| modules (<code>mod_alias</code> etc.) so if they are used then |
| <code>mod_rewrite</code> must be configured to accommodate |
| them. Also, mome magic must be performed to do a |
| per-dynamic-virtual-host equivalent of |
| <code>ScriptAlias</code>.</p> |
| <pre> |
| # get the server name from the Host: header |
| UseCanonicalName Off |
| |
| # splittable logs |
| LogFormat "%{Host}i %h %l %u %t \"%r\" %s %b" vcommon |
| CustomLog logs/access_log vcommon |
| |
| <Directory /www/hosts> |
| # ExecCGI is needed here because we can't force |
| # CGI execution in the way that ScriptAlias does |
| Options FollowSymLinks ExecCGI |
| </Directory> |
| |
| # now for the hard bit |
| |
| RewriteEngine On |
| |
| # a ServerName derived from a Host: header may be any case at all |
| RewriteMap lowercase int:tolower |
| |
| ## deal with normal documents first: |
| # allow Alias /icons/ to work - repeat for other aliases |
| RewriteCond %{REQUEST_URI} !^/icons/ |
| # allow CGIs to work |
| RewriteCond %{REQUEST_URI} !^/cgi-bin/ |
| # do the magic |
| RewriteRule ^/(.*)$ /www/hosts/${lowercase:%{SERVER_NAME}}/docs/$1 |
| |
| ## and now deal with CGIs - we have to force a MIME type |
| RewriteCond %{REQUEST_URI} ^/cgi-bin/ |
| RewriteRule ^/(.*)$ /www/hosts/${lowercase:%{SERVER_NAME}}/cgi-bin/$1 [T=application/x-httpd-cgi] |
| |
| # that's it! |
| </pre> |
| <hr /> |
| |
| <h2><a id="homepages.rewrite" name="homepages.rewrite">A |
| homepages system using <code>mod_rewrite</code></a></h2> |
| |
| <p>This does the same thing as <a href="#homepages">the second |
| example</a>.</p> |
| <pre> |
| RewriteEngine on |
| |
| RewriteMap lowercase int:tolower |
| |
| # allow CGIs to work |
| RewriteCond %{REQUEST_URI} !^/cgi-bin/ |
| |
| # check the hostname is right so that the RewriteRule works |
| RewriteCond ${lowercase:%{SERVER_NAME}} ^www\.[a-z-]+\.isp\.com$ |
| |
| # concatenate the virtual host name onto the start of the URI |
| # the [C] means do the next rewrite on the result of this one |
| RewriteRule ^(.+) ${lowercase:%{SERVER_NAME}}$1 [C] |
| |
| # now create the real file name |
| RewriteRule ^www\.([a-z-]+)\.isp\.com/(.*) /home/$1/$2 |
| |
| # define the global CGI directory |
| ScriptAlias /cgi-bin/ /www/std-cgi/ |
| </pre> |
| <hr /> |
| |
| <h2><a id="xtra-conf" name="xtra-conf">Using a separate virtual |
| host configuration file</a></h2> |
| |
| <p>This arrangement uses more advanced <code>mod_rewrite</code> |
| features to get the translation from virtual host to document |
| root from a separate configuration file. This provides more |
| flexibility but requires more complicated configuration.</p> |
| |
| <p>The <code>vhost.map</code> file contains something like |
| this:</p> |
| <pre> |
| www.customer-1.com /www/customers/1 |
| www.customer-2.com /www/customers/2 |
| # ... |
| www.customer-N.com /www/customers/N |
| </pre> |
| <br /> |
| <br /> |
| |
| |
| <p>The <code>http.conf</code> contains this:</p> |
| <pre> |
| RewriteEngine on |
| |
| RewriteMap lowercase int:tolower |
| |
| # define the map file |
| RewriteMap vhost txt:/www/conf/vhost.map |
| |
| # deal with aliases as above |
| RewriteCond %{REQUEST_URI} !^/icons/ |
| RewriteCond %{REQUEST_URI} !^/cgi-bin/ |
| RewriteCond ${lowercase:%{SERVER_NAME}} ^(.+)$ |
| # this does the file-based remap |
| RewriteCond ${vhost:%1} ^(/.*)$ |
| RewriteRule ^/(.*)$ %1/docs/$1 |
| |
| RewriteCond %{REQUEST_URI} ^/cgi-bin/ |
| RewriteCond ${lowercase:%{SERVER_NAME}} ^(.+)$ |
| RewriteCond ${vhost:%1} ^(/.*)$ |
| RewriteRule ^/(.*)$ %1/cgi-bin/$1 |
| </pre> |
| <br /> |
| <br /> |
| <!--#include virtual="footer.html" --> |
| </body> |
| </html> |
| |