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<?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!-- XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX This file is generated from xml source: DO NOT EDIT XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX --> <title>URL Rewriting Guide - Advanced topics - Apache HTTP Server</title> <link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> <link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> <link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /> <link href="../images/favicon.ico" rel="shortcut icon" /></head> <body id="manual-page"><div id="page-header"> <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p> <p class="apache">Apache HTTP Server Version 2.2</p> <img alt="" src="../images/feather.gif" /></div> <div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div> <div id="path"> <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.2</a> > <a href="./">Rewrite</a></div><div id="page-content"><div id="preamble"><h1>URL Rewriting Guide - Advanced topics</h1> <div class="toplang"> <p><span>Available Languages: </span><a href="../en/rewrite/rewrite_guide_advanced.html" title="English"> en </a></p> </div> <p>This document supplements the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> <a href="../mod/mod_rewrite.html">reference documentation</a>. It describes how one can use Apache's <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> to solve typical URL-based problems with which webmasters are commonly confronted. We give detailed descriptions on how to solve each problem by configuring URL rewriting rulesets.</p> <div class="warning">ATTENTION: Depending on your server configuration it may be necessary to adjust the examples for your situation, e.g., adding the <code>[PT]</code> flag if using <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> and <code class="module"><a href="../mod/mod_userdir.html">mod_userdir</a></code>, etc. Or rewriting a ruleset to work in <code>.htaccess</code> context instead of per-server context. Always try to understand what a particular ruleset really does before you use it; this avoids many problems.</div> </div> <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#cluster">Web Cluster with Consistent URL Space</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#structuredhomedirs">Structured Homedirs</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#filereorg">Filesystem Reorganization</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#redirect404">Redirect Failing URLs to Another Web Server</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#archive-access-multiplexer">Archive Access Multiplexer</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#browser-dependent-content">Browser Dependent Content</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#dynamic-mirror">Dynamic Mirror</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#reverse-dynamic-mirror">Reverse Dynamic Mirror</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#retrieve-missing-data">Retrieve Missing Data from Intranet</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#load-balancing">Load Balancing</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#new-mime-type">New MIME-type, New Service</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#on-the-fly-content">On-the-fly Content-Regeneration</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#autorefresh">Document With Autorefresh</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#mass-virtual-hosting">Mass Virtual Hosting</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#host-deny">Host Deny</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#proxy-deny">Proxy Deny</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#special-authentication">Special Authentication Variant</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#referer-deflector">Referer-based Deflector</a></li> </ul><h3>See also</h3><ul class="seealso"><li><a href="../mod/mod_rewrite.html">Module documentation</a></li><li><a href="rewrite_intro.html">mod_rewrite introduction</a></li><li><a href="rewrite_guide.html">Rewrite Guide - useful examples</a></li><li><a href="rewrite_tech.html">Technical details</a></li></ul></div> <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="cluster" id="cluster">Web Cluster with Consistent URL Space</a></h2> <dl> <dt>Description:</dt> <dd> <p>We want to create a homogeneous and consistent URL layout across all WWW servers on an Intranet web cluster, i.e., all URLs (by definition server-local and thus server-dependent!) become server <em>independent</em>! What we want is to give the WWW namespace a single consistent layout: no URL should refer to any particular target server. The cluster itself should connect users automatically to a physical target host as needed, invisibly.</p> </dd> <dt>Solution:</dt> <dd> <p>First, the knowledge of the target servers comes from (distributed) external maps which contain information on where our users, groups, and entities reside. They have the form:</p> <div class="example"><pre> user1 server_of_user1 user2 server_of_user2 : : </pre></div> <p>We put them into files <code>map.xxx-to-host</code>. Second we need to instruct all servers to redirect URLs of the forms:</p> <div class="example"><pre> /u/user/anypath /g/group/anypath /e/entity/anypath </pre></div> <p>to</p> <div class="example"><pre> http://physical-host/u/user/anypath http://physical-host/g/group/anypath http://physical-host/e/entity/anypath </pre></div> <p>when any URL path need not be valid on every server. The following ruleset does this for us with the help of the map files (assuming that server0 is a default server which will be used if a user has no entry in the map):</p> <div class="example"><pre> RewriteEngine on RewriteMap user-to-host txt:/path/to/map.user-to-host RewriteMap group-to-host txt:/path/to/map.group-to-host RewriteMap entity-to-host txt:/path/to/map.entity-to-host RewriteRule ^/u/<strong>([^/]+)</strong>/?(.*) http://<strong>${user-to-host:$1|server0}</strong>/u/$1/$2 RewriteRule ^/g/<strong>([^/]+)</strong>/?(.*) http://<strong>${group-to-host:$1|server0}</strong>/g/$1/$2 RewriteRule ^/e/<strong>([^/]+)</strong>/?(.*) http://<strong>${entity-to-host:$1|server0}</strong>/e/$1/$2 RewriteRule ^/([uge])/([^/]+)/?$ /$1/$2/.www/ RewriteRule ^/([uge])/([^/]+)/([^.]+.+) /$1/$2/.www/$3\ </pre></div> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="structuredhomedirs" id="structuredhomedirs">Structured Homedirs</a></h2> <dl> <dt>Description:</dt> <dd> <p>Some sites with thousands of users use a structured homedir layout, <em>i.e.</em> each homedir is in a subdirectory which begins (for instance) with the first character of the username. So, <code>/~foo/anypath</code> is <code>/home/<strong>f</strong>/foo/.www/anypath</code> while <code>/~bar/anypath</code> is <code>/home/<strong>b</strong>/bar/.www/anypath</code>.</p> </dd> <dt>Solution:</dt> <dd> <p>We use the following ruleset to expand the tilde URLs into the above layout.</p> <div class="example"><pre> RewriteEngine on RewriteRule ^/~(<strong>([a-z])</strong>[a-z0-9]+)(.*) /home/<strong>$2</strong>/$1/.www$3 </pre></div> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="filereorg" id="filereorg">Filesystem Reorganization</a></h2> <dl> <dt>Description:</dt> <dd> <p>This really is a hardcore example: a killer application which heavily uses per-directory <code>RewriteRules</code> to get a smooth look and feel on the Web while its data structure is never touched or adjusted. Background: <strong><em>net.sw</em></strong> is my archive of freely available Unix software packages, which I started to collect in 1992. It is both my hobby and job to do this, because while I'm studying computer science I have also worked for many years as a system and network administrator in my spare time. Every week I need some sort of software so I created a deep hierarchy of directories where I stored the packages:</p> <div class="example"><pre> drwxrwxr-x 2 netsw users 512 Aug 3 18:39 Audio/ drwxrwxr-x 2 netsw users 512 Jul 9 14:37 Benchmark/ drwxrwxr-x 12 netsw users 512 Jul 9 00:34 Crypto/ drwxrwxr-x 5 netsw users 512 Jul 9 00:41 Database/ drwxrwxr-x 4 netsw users 512 Jul 30 19:25 Dicts/ drwxrwxr-x 10 netsw users 512 Jul 9 01:54 Graphic/ drwxrwxr-x 5 netsw users 512 Jul 9 01:58 Hackers/ drwxrwxr-x 8 netsw users 512 Jul 9 03:19 InfoSys/ drwxrwxr-x 3 netsw users 512 Jul 9 03:21 Math/ drwxrwxr-x 3 netsw users 512 Jul 9 03:24 Misc/ drwxrwxr-x 9 netsw users 512 Aug 1 16:33 Network/ drwxrwxr-x 2 netsw users 512 Jul 9 05:53 Office/ drwxrwxr-x 7 netsw users 512 Jul 9 09:24 SoftEng/ drwxrwxr-x 7 netsw users 512 Jul 9 12:17 System/ drwxrwxr-x 12 netsw users 512 Aug 3 20:15 Typesetting/ drwxrwxr-x 10 netsw users 512 Jul 9 14:08 X11/ </pre></div> <p>In July 1996 I decided to make this archive public to the world via a nice Web interface. "Nice" means that I wanted to offer an interface where you can browse directly through the archive hierarchy. And "nice" means that I didn't want to change anything inside this hierarchy - not even by putting some CGI scripts at the top of it. Why? Because the above structure should later be accessible via FTP as well, and I didn't want any Web or CGI stuff mixed in there.</p> </dd> <dt>Solution:</dt> <dd> <p>The solution has two parts: The first is a set of CGI scripts which create all the pages at all directory levels on-the-fly. I put them under <code>/e/netsw/.www/</code> as follows:</p> <div class="example"><pre> -rw-r--r-- 1 netsw users 1318 Aug 1 18:10 .wwwacl drwxr-xr-x 18 netsw users 512 Aug 5 15:51 DATA/ -rw-rw-rw- 1 netsw users 372982 Aug 5 16:35 LOGFILE -rw-r--r-- 1 netsw users 659 Aug 4 09:27 TODO -rw-r--r-- 1 netsw users 5697 Aug 1 18:01 netsw-about.html -rwxr-xr-x 1 netsw users 579 Aug 2 10:33 netsw-access.pl -rwxr-xr-x 1 netsw users 1532 Aug 1 17:35 netsw-changes.cgi -rwxr-xr-x 1 netsw users 2866 Aug 5 14:49 netsw-home.cgi drwxr-xr-x 2 netsw users 512 Jul 8 23:47 netsw-img/ -rwxr-xr-x 1 netsw users 24050 Aug 5 15:49 netsw-lsdir.cgi -rwxr-xr-x 1 netsw users 1589 Aug 3 18:43 netsw-search.cgi -rwxr-xr-x 1 netsw users 1885 Aug 1 17:41 netsw-tree.cgi -rw-r--r-- 1 netsw users 234 Jul 30 16:35 netsw-unlimit.lst </pre></div> <p>The <code>DATA/</code> subdirectory holds the above directory structure, <em>i.e.</em> the real <strong><em>net.sw</em></strong> stuff, and gets automatically updated via <code>rdist</code> from time to time. The second part of the problem remains: how to link these two structures together into one smooth-looking URL tree? We want to hide the <code>DATA/</code> directory from the user while running the appropriate CGI scripts for the various URLs. Here is the solution: first I put the following into the per-directory configuration file in the <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code> of the server to rewrite the public URL path <code>/net.sw/</code> to the internal path <code>/e/netsw</code>:</p> <div class="example"><pre> RewriteRule ^net.sw$ net.sw/ [R] RewriteRule ^net.sw/(.*)$ e/netsw/$1 </pre></div> <p>The first rule is for requests which miss the trailing slash! The second rule does the real thing. And then comes the killer configuration which stays in the per-directory config file <code>/e/netsw/.www/.wwwacl</code>:</p> <div class="example"><pre> Options ExecCGI FollowSymLinks Includes MultiViews RewriteEngine on # we are reached via /net.sw/ prefix RewriteBase /net.sw/ # first we rewrite the root dir to # the handling cgi script RewriteRule ^$ netsw-home.cgi [L] RewriteRule ^index\.html$ netsw-home.cgi [L] # strip out the subdirs when # the browser requests us from perdir pages RewriteRule ^.+/(netsw-[^/]+/.+)$ $1 [L] # and now break the rewriting for local files RewriteRule ^netsw-home\.cgi.* - [L] RewriteRule ^netsw-changes\.cgi.* - [L] RewriteRule ^netsw-search\.cgi.* - [L] RewriteRule ^netsw-tree\.cgi$ - [L] RewriteRule ^netsw-about\.html$ - [L] RewriteRule ^netsw-img/.*$ - [L] # anything else is a subdir which gets handled # by another cgi script RewriteRule !^netsw-lsdir\.cgi.* - [C] RewriteRule (.*) netsw-lsdir.cgi/$1 </pre></div> <p>Some hints for interpretation:</p> <ol> <li>Notice the <code>L</code> (last) flag and no substitution field ('<code>-</code>') in the fourth part</li> <li>Notice the <code>!</code> (not) character and the <code>C</code> (chain) flag at the first rule in the last part</li> <li>Notice the catch-all pattern in the last rule</li> </ol> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="redirect404" id="redirect404">Redirect Failing URLs to Another Web Server</a></h2> <dl> <dt>Description:</dt> <dd> <p>A typical FAQ about URL rewriting is how to redirect failing requests on webserver A to webserver B. Usually this is done via <code class="directive"><a href="../mod/core.html#errordocument">ErrorDocument</a></code> CGI scripts in Perl, but there is also a <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> solution. But note that this performs more poorly than using an <code class="directive"><a href="../mod/core.html#errordocument">ErrorDocument</a></code> CGI script!</p> </dd> <dt>Solution:</dt> <dd> <p>The first solution has the best performance but less flexibility, and is less safe:</p> <div class="example"><pre> RewriteEngine on RewriteCond /your/docroot/%{REQUEST_FILENAME} <strong>!-f</strong> RewriteRule ^(.+) http://<strong>webserverB</strong>.dom/$1 </pre></div> <p>The problem here is that this will only work for pages inside the <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code>. While you can add more Conditions (for instance to also handle homedirs, etc.) there is a better variant:</p> <div class="example"><pre> RewriteEngine on RewriteCond %{REQUEST_URI} <strong>!-U</strong> RewriteRule ^(.+) http://<strong>webserverB</strong>.dom/$1 </pre></div> <p>This uses the URL look-ahead feature of <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>. The result is that this will work for all types of URLs and is safe. But it does have a performance impact on the web server, because for every request there is one more internal subrequest. So, if your web server runs on a powerful CPU, use this one. If it is a slow machine, use the first approach or better an <code class="directive"><a href="../mod/core.html#errordocument">ErrorDocument</a></code> CGI script.</p> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="archive-access-multiplexer" id="archive-access-multiplexer">Archive Access Multiplexer</a></h2> <dl> <dt>Description:</dt> <dd> <p>Do you know the great CPAN (Comprehensive Perl Archive Network) under <a href="http://www.perl.com/CPAN">http://www.perl.com/CPAN</a>? CPAN automatically redirects browsers to one of many FTP servers around the world (generally one near the requesting client); each server carries a full CPAN mirror. This is effectively an FTP access multiplexing service. CPAN runs via CGI scripts, but how could a similar approach be implemented via <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>?</p> </dd> <dt>Solution:</dt> <dd> <p>First we notice that as of version 3.0.0, <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> can also use the "<code>ftp:</code>" scheme on redirects. And second, the location approximation can be done by a <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> over the top-level domain of the client. With a tricky chained ruleset we can use this top-level domain as a key to our multiplexing map.</p> <div class="example"><pre> RewriteEngine on RewriteMap multiplex txt:/path/to/map.cxan RewriteRule ^/CxAN/(.*) %{REMOTE_HOST}::$1 [C] RewriteRule ^.+\.<strong>([a-zA-Z]+)</strong>::(.*)$ ${multiplex:<strong>$1</strong>|ftp.default.dom}$2 [R,L] </pre></div> <div class="example"><pre> ## ## map.cxan -- Multiplexing Map for CxAN ## de ftp://ftp.cxan.de/CxAN/ uk ftp://ftp.cxan.uk/CxAN/ com ftp://ftp.cxan.com/CxAN/ : ##EOF## </pre></div> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="browser-dependent-content" id="browser-dependent-content">Browser Dependent Content</a></h2> <dl> <dt>Description:</dt> <dd> <p>At least for important top-level pages it is sometimes necessary to provide the optimum of browser dependent content, i.e., one has to provide one version for current browsers, a different version for the Lynx and text-mode browsers, and another for other browsers.</p> </dd> <dt>Solution:</dt> <dd> <p>We cannot use content negotiation because the browsers do not provide their type in that form. Instead we have to act on the HTTP header "User-Agent". The following config does the following: If the HTTP header "User-Agent" begins with "Mozilla/3", the page <code>foo.html</code> is rewritten to <code>foo.NS.html</code> and the rewriting stops. If the browser is "Lynx" or "Mozilla" of version 1 or 2, the URL becomes <code>foo.20.html</code>. All other browsers receive page <code>foo.32.html</code>. This is done with the following ruleset:</p> <div class="example"><pre> RewriteCond %{HTTP_USER_AGENT} ^<strong>Mozilla/3</strong>.* RewriteRule ^foo\.html$ foo.<strong>NS</strong>.html [<strong>L</strong>] RewriteCond %{HTTP_USER_AGENT} ^<strong>Lynx/</strong>.* [OR] RewriteCond %{HTTP_USER_AGENT} ^<strong>Mozilla/[12]</strong>.* RewriteRule ^foo\.html$ foo.<strong>20</strong>.html [<strong>L</strong>] RewriteRule ^foo\.html$ foo.<strong>32</strong>.html [<strong>L</strong>] </pre></div> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="dynamic-mirror" id="dynamic-mirror">Dynamic Mirror</a></h2> <dl> <dt>Description:</dt> <dd> <p>Assume there are nice web pages on remote hosts we want to bring into our namespace. For FTP servers we would use the <code>mirror</code> program which actually maintains an explicit up-to-date copy of the remote data on the local machine. For a web server we could use the program <code>webcopy</code> which runs via HTTP. But both techniques have a major drawback: The local copy is always only as up-to-date as the last time we ran the program. It would be much better if the mirror was not a static one we have to establish explicitly. Instead we want a dynamic mirror with data which gets updated automatically as needed on the remote host(s).</p> </dd> <dt>Solution:</dt> <dd> <p>To provide this feature we map the remote web page or even the complete remote web area to our namespace by the use of the <dfn>Proxy Throughput</dfn> feature (flag <code>[P]</code>):</p> <div class="example"><pre> RewriteEngine on RewriteBase /~quux/ RewriteRule ^<strong>hotsheet/</strong>(.*)$ <strong>http://www.tstimpreso.com/hotsheet/</strong>$1 [<strong>P</strong>] </pre></div> <div class="example"><pre> RewriteEngine on RewriteBase /~quux/ RewriteRule ^<strong>usa-news\.html</strong>$ <strong>http://www.quux-corp.com/news/index.html</strong> [<strong>P</strong>] </pre></div> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="reverse-dynamic-mirror" id="reverse-dynamic-mirror">Reverse Dynamic Mirror</a></h2> <dl> <dt>Description:</dt> <dd>...</dd> <dt>Solution:</dt> <dd> <div class="example"><pre> RewriteEngine on RewriteCond /mirror/of/remotesite/$1 -U RewriteRule ^http://www\.remotesite\.com/(.*)$ /mirror/of/remotesite/$1 </pre></div> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="retrieve-missing-data" id="retrieve-missing-data">Retrieve Missing Data from Intranet</a></h2> <dl> <dt>Description:</dt> <dd> <p>This is a tricky way of virtually running a corporate (external) Internet web server (<code>www.quux-corp.dom</code>), while actually keeping and maintaining its data on an (internal) Intranet web server (<code>www2.quux-corp.dom</code>) which is protected by a firewall. The trick is that the external web server retrieves the requested data on-the-fly from the internal one.</p> </dd> <dt>Solution:</dt> <dd> <p>First, we must make sure that our firewall still protects the internal web server and only the external web server is allowed to retrieve data from it. On a packet-filtering firewall, for instance, we could configure a firewall ruleset like the following:</p> <div class="example"><pre> <strong>ALLOW</strong> Host www.quux-corp.dom Port >1024 --> Host www2.quux-corp.dom Port <strong>80</strong> <strong>DENY</strong> Host * Port * --> Host www2.quux-corp.dom Port <strong>80</strong> </pre></div> <p>Just adjust it to your actual configuration syntax. Now we can establish the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> rules which request the missing data in the background through the proxy throughput feature:</p> <div class="example"><pre> RewriteRule ^/~([^/]+)/?(.*) /home/$1/.www/$2 RewriteCond %{REQUEST_FILENAME} <strong>!-f</strong> RewriteCond %{REQUEST_FILENAME} <strong>!-d</strong> RewriteRule ^/home/([^/]+)/.www/?(.*) http://<strong>www2</strong>.quux-corp.dom/~$1/pub/$2 [<strong>P</strong>] </pre></div> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="load-balancing" id="load-balancing">Load Balancing</a></h2> <dl> <dt>Description:</dt> <dd> <p>Suppose we want to load balance the traffic to <code>www.example.com</code> over <code>www[0-5].example.com</code> (a total of 6 servers). How can this be done?</p> </dd> <dt>Solution:</dt> <dd> <p>There are many possible solutions for this problem. We will first discuss a common DNS-based method, and then one based on <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>:</p> <ol> <li> <strong>DNS Round-Robin</strong> <p>The simplest method for load-balancing is to use DNS round-robin. Here you just configure <code>www[0-9].example.com</code> as usual in your DNS with A (address) records, e.g.,</p> <div class="example"><pre> www0 IN A 1.2.3.1 www1 IN A 1.2.3.2 www2 IN A 1.2.3.3 www3 IN A 1.2.3.4 www4 IN A 1.2.3.5 www5 IN A 1.2.3.6 </pre></div> <p>Then you additionally add the following entries:</p> <div class="example"><pre> www IN A 1.2.3.1 www IN A 1.2.3.2 www IN A 1.2.3.3 www IN A 1.2.3.4 www IN A 1.2.3.5 </pre></div> <p>Now when <code>www.example.com</code> gets resolved, <code>BIND</code> gives out <code>www0-www5</code> - but in a permutated (rotated) order every time. This way the clients are spread over the various servers. But notice that this is not a perfect load balancing scheme, because DNS resolutions are cached by clients and other nameservers, so once a client has resolved <code>www.example.com</code> to a particular <code>wwwN.example.com</code>, all its subsequent requests will continue to go to the same IP (and thus a single server), rather than being distributed across the other available servers. But the overall result is okay because the requests are collectively spread over the various web servers.</p> </li> <li> <strong>DNS Load-Balancing</strong> <p>A sophisticated DNS-based method for load-balancing is to use the program <code>lbnamed</code> which can be found at <a href="http://www.stanford.edu/~riepel/lbnamed/"> http://www.stanford.edu/~riepel/lbnamed/</a>. It is a Perl 5 program which, in conjunction with auxilliary tools, provides real load-balancing via DNS.</p> </li> <li> <strong>Proxy Throughput Round-Robin</strong> <p>In this variant we use <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> and its proxy throughput feature. First we dedicate <code>www0.example.com</code> to be actually <code>www.example.com</code> by using a single</p> <div class="example"><pre> www IN CNAME www0.example.com. </pre></div> <p>entry in the DNS. Then we convert <code>www0.example.com</code> to a proxy-only server, i.e., we configure this machine so all arriving URLs are simply passed through its internal proxy to one of the 5 other servers (<code>www1-www5</code>). To accomplish this we first establish a ruleset which contacts a load balancing script <code>lb.pl</code> for all URLs.</p> <div class="example"><pre> RewriteEngine on RewriteMap lb prg:/path/to/lb.pl RewriteRule ^/(.+)$ ${lb:$1} [P,L] </pre></div> <p>Then we write <code>lb.pl</code>:</p> <div class="example"><pre> #!/path/to/perl ## ## lb.pl -- load balancing script ## $| = 1; $name = "www"; # the hostname base $first = 1; # the first server (not 0 here, because 0 is myself) $last = 5; # the last server in the round-robin $domain = "foo.dom"; # the domainname $cnt = 0; while (<STDIN>) { $cnt = (($cnt+1) % ($last+1-$first)); $server = sprintf("%s%d.%s", $name, $cnt+$first, $domain); print "http://$server/$_"; } ##EOF## </pre></div> <div class="note">A last notice: Why is this useful? Seems like <code>www0.example.com</code> still is overloaded? The answer is yes, it is overloaded, but with plain proxy throughput requests, only! All SSI, CGI, ePerl, etc. processing is handled done on the other machines. For a complicated site, this may work well. The biggest risk here is that www0 is now a single point of failure -- if it crashes, the other servers are inaccessible.</div> </li> <li> <strong>Dedicated Load Balancers</strong> <p>There are more sophisticated solutions, as well. Cisco, F5, and several other companies sell hardware load balancers (typically used in pairs for redundancy), which offer sophisticated load balancing and auto-failover features. There are software packages which offer similar features on commodity hardware, as well. If you have enough money or need, check these out. The <a href="http://vegan.net/lb/">lb-l mailing list</a> is a good place to research.</p> </li> </ol> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="new-mime-type" id="new-mime-type">New MIME-type, New Service</a></h2> <dl> <dt>Description:</dt> <dd> <p>On the net there are many nifty CGI programs. But their usage is usually boring, so a lot of webmasters don't use them. Even Apache's Action handler feature for MIME-types is only appropriate when the CGI programs don't need special URLs (actually <code>PATH_INFO</code> and <code>QUERY_STRINGS</code>) as their input. First, let us configure a new file type with extension <code>.scgi</code> (for secure CGI) which will be processed by the popular <code>cgiwrap</code> program. The problem here is that for instance if we use a Homogeneous URL Layout (see above) a file inside the user homedirs might have a URL like <code>/u/user/foo/bar.scgi</code>, but <code>cgiwrap</code> needs URLs in the form <code>/~user/foo/bar.scgi/</code>. The following rule solves the problem:</p> <div class="example"><pre> RewriteRule ^/[uge]/<strong>([^/]+)</strong>/\.www/(.+)\.scgi(.*) ... ... /internal/cgi/user/cgiwrap/~<strong>$1</strong>/$2.scgi$3 [NS,<strong>T=application/x-http-cgi</strong>] </pre></div> <p>Or assume we have some more nifty programs: <code>wwwlog</code> (which displays the <code>access.log</code> for a URL subtree) and <code>wwwidx</code> (which runs Glimpse on a URL subtree). We have to provide the URL area to these programs so they know which area they are really working with. But usually this is complicated, because they may still be requested by the alternate URL form, i.e., typically we would run the <code>swwidx</code> program from within <code>/u/user/foo/</code> via hyperlink to</p> <div class="example"><pre> /internal/cgi/user/swwidx?i=/u/user/foo/ </pre></div> <p>which is ugly, because we have to hard-code <strong>both</strong> the location of the area <strong>and</strong> the location of the CGI inside the hyperlink. When we have to reorganize, we spend a lot of time changing the various hyperlinks.</p> </dd> <dt>Solution:</dt> <dd> <p>The solution here is to provide a special new URL format which automatically leads to the proper CGI invocation. We configure the following:</p> <div class="example"><pre> RewriteRule ^/([uge])/([^/]+)(/?.*)/\* /internal/cgi/user/wwwidx?i=/$1/$2$3/ RewriteRule ^/([uge])/([^/]+)(/?.*):log /internal/cgi/user/wwwlog?f=/$1/$2$3 </pre></div> <p>Now the hyperlink to search at <code>/u/user/foo/</code> reads only</p> <div class="example"><pre> HREF="*" </pre></div> <p>which internally gets automatically transformed to</p> <div class="example"><pre> /internal/cgi/user/wwwidx?i=/u/user/foo/ </pre></div> <p>The same approach leads to an invocation for the access log CGI program when the hyperlink <code>:log</code> gets used.</p> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="on-the-fly-content" id="on-the-fly-content">On-the-fly Content-Regeneration</a></h2> <dl> <dt>Description:</dt> <dd> <p>Here comes a really esoteric feature: Dynamically generated but statically served pages, i.e., pages should be delivered as pure static pages (read from the filesystem and just passed through), but they have to be generated dynamically by the web server if missing. This way you can have CGI-generated pages which are statically served unless an admin (or a <code>cron</code> job) removes the static contents. Then the contents gets refreshed.</p> </dd> <dt>Solution:</dt> <dd> This is done via the following ruleset: <div class="example"><pre> RewriteCond %{REQUEST_FILENAME} <strong>!-s</strong> RewriteRule ^page\.<strong>html</strong>$ page.<strong>cgi</strong> [T=application/x-httpd-cgi,L] </pre></div> <p>Here a request for <code>page.html</code> leads to an internal run of a corresponding <code>page.cgi</code> if <code>page.html</code> is missing or has filesize null. The trick here is that <code>page.cgi</code> is a CGI script which (additionally to its <code>STDOUT</code>) writes its output to the file <code>page.html</code>. Once it has completed, the server sends out <code>page.html</code>. When the webmaster wants to force a refresh of the contents, he just removes <code>page.html</code> (typically from <code>cron</code>).</p> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="autorefresh" id="autorefresh">Document With Autorefresh</a></h2> <dl> <dt>Description:</dt> <dd> <p>Wouldn't it be nice, while creating a complex web page, if the web browser would automatically refresh the page every time we save a new version from within our editor? Impossible?</p> </dd> <dt>Solution:</dt> <dd> <p>No! We just combine the MIME multipart feature, the web server NPH feature, and the URL manipulation power of <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>. First, we establish a new URL feature: Adding just <code>:refresh</code> to any URL causes the 'page' to be refreshed every time it is updated on the filesystem.</p> <div class="example"><pre> RewriteRule ^(/[uge]/[^/]+/?.*):refresh /internal/cgi/apache/nph-refresh?f=$1 </pre></div> <p>Now when we reference the URL</p> <div class="example"><pre> /u/foo/bar/page.html:refresh </pre></div> <p>this leads to the internal invocation of the URL</p> <div class="example"><pre> /internal/cgi/apache/nph-refresh?f=/u/foo/bar/page.html </pre></div> <p>The only missing part is the NPH-CGI script. Although one would usually say "left as an exercise to the reader" ;-) I will provide this, too.</p> <div class="example"><pre> #!/sw/bin/perl ## ## nph-refresh -- NPH/CGI script for auto refreshing pages ## Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved. ## $| = 1; # split the QUERY_STRING variable @pairs = split(/&/, $ENV{'QUERY_STRING'}); foreach $pair (@pairs) { ($name, $value) = split(/=/, $pair); $name =~ tr/A-Z/a-z/; $name = 'QS_' . $name; $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg; eval "\$$name = \"$value\""; } $QS_s = 1 if ($QS_s eq ''); $QS_n = 3600 if ($QS_n eq ''); if ($QS_f eq '') { print "HTTP/1.0 200 OK\n"; print "Content-type: text/html\n\n"; print "&lt;b&gt;ERROR&lt;/b&gt;: No file given\n"; exit(0); } if (! -f $QS_f) { print "HTTP/1.0 200 OK\n"; print "Content-type: text/html\n\n"; print "&lt;b&gt;ERROR&lt;/b&gt;: File $QS_f not found\n"; exit(0); } sub print_http_headers_multipart_begin { print "HTTP/1.0 200 OK\n"; $bound = "ThisRandomString12345"; print "Content-type: multipart/x-mixed-replace;boundary=$bound\n"; &print_http_headers_multipart_next; } sub print_http_headers_multipart_next { print "\n--$bound\n"; } sub print_http_headers_multipart_end { print "\n--$bound--\n"; } sub displayhtml { local($buffer) = @_; $len = length($buffer); print "Content-type: text/html\n"; print "Content-length: $len\n\n"; print $buffer; } sub readfile { local($file) = @_; local(*FP, $size, $buffer, $bytes); ($x, $x, $x, $x, $x, $x, $x, $size) = stat($file); $size = sprintf("%d", $size); open(FP, "&lt;$file"); $bytes = sysread(FP, $buffer, $size); close(FP); return $buffer; } $buffer = &readfile($QS_f); &print_http_headers_multipart_begin; &displayhtml($buffer); sub mystat { local($file) = $_[0]; local($time); ($x, $x, $x, $x, $x, $x, $x, $x, $x, $mtime) = stat($file); return $mtime; } $mtimeL = &mystat($QS_f); $mtime = $mtime; for ($n = 0; $n &lt; $QS_n; $n++) { while (1) { $mtime = &mystat($QS_f); if ($mtime ne $mtimeL) { $mtimeL = $mtime; sleep(2); $buffer = &readfile($QS_f); &print_http_headers_multipart_next; &displayhtml($buffer); sleep(5); $mtimeL = &mystat($QS_f); last; } sleep($QS_s); } } &print_http_headers_multipart_end; exit(0); ##EOF## </pre></div> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="mass-virtual-hosting" id="mass-virtual-hosting">Mass Virtual Hosting</a></h2> <dl> <dt>Description:</dt> <dd> <p>The <code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code> feature of Apache is nice and works great when you just have a few dozen virtual hosts. But when you are an ISP and have hundreds of virtual hosts, this feature is suboptimal.</p> </dd> <dt>Solution:</dt> <dd> <p>To provide this feature we map the remote web page or even the complete remote web area to our namespace using the <dfn>Proxy Throughput</dfn> feature (flag <code>[P]</code>):</p> <div class="example"><pre> ## ## vhost.map ## www.vhost1.dom:80 /path/to/docroot/vhost1 www.vhost2.dom:80 /path/to/docroot/vhost2 : www.vhostN.dom:80 /path/to/docroot/vhostN </pre></div> <div class="example"><pre> ## ## httpd.conf ## : # use the canonical hostname on redirects, etc. UseCanonicalName on : # add the virtual host in front of the CLF-format CustomLog /path/to/access_log "%{VHOST}e %h %l %u %t \"%r\" %>s %b" : # enable the rewriting engine in the main server RewriteEngine on # define two maps: one for fixing the URL and one which defines # the available virtual hosts with their corresponding # DocumentRoot. RewriteMap lowercase int:tolower RewriteMap vhost txt:/path/to/vhost.map # Now do the actual virtual host mapping # via a huge and complicated single rule: # # 1. make sure we don't map for common locations RewriteCond %{REQUEST_URI} !^/commonurl1/.* RewriteCond %{REQUEST_URI} !^/commonurl2/.* : RewriteCond %{REQUEST_URI} !^/commonurlN/.* # # 2. make sure we have a Host header, because # currently our approach only supports # virtual hosting through this header RewriteCond %{HTTP_HOST} !^$ # # 3. lowercase the hostname RewriteCond ${lowercase:%{HTTP_HOST}|NONE} ^(.+)$ # # 4. lookup this hostname in vhost.map and # remember it only when it is a path # (and not "NONE" from above) RewriteCond ${vhost:%1} ^(/.*)$ # # 5. finally we can map the URL to its docroot location # and remember the virtual host for logging purposes RewriteRule ^/(.*)$ %1/$1 [E=VHOST:${lowercase:%{HTTP_HOST}}] : </pre></div> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="host-deny" id="host-deny">Host Deny</a></h2> <dl> <dt>Description:</dt> <dd> <p>How can we forbid a list of externally configured hosts from using our server?</p> </dd> <dt>Solution:</dt> <dd> <p>For Apache >= 1.3b6:</p> <div class="example"><pre> RewriteEngine on RewriteMap hosts-deny txt:/path/to/hosts.deny RewriteCond ${hosts-deny:%{REMOTE_HOST}|NOT-FOUND} !=NOT-FOUND [OR] RewriteCond ${hosts-deny:%{REMOTE_ADDR}|NOT-FOUND} !=NOT-FOUND RewriteRule ^/.* - [F] </pre></div> <p>For Apache <= 1.3b6:</p> <div class="example"><pre> RewriteEngine on RewriteMap hosts-deny txt:/path/to/hosts.deny RewriteRule ^/(.*)$ ${hosts-deny:%{REMOTE_HOST}|NOT-FOUND}/$1 RewriteRule !^NOT-FOUND/.* - [F] RewriteRule ^NOT-FOUND/(.*)$ ${hosts-deny:%{REMOTE_ADDR}|NOT-FOUND}/$1 RewriteRule !^NOT-FOUND/.* - [F] RewriteRule ^NOT-FOUND/(.*)$ /$1 </pre></div> <div class="example"><pre> ## ## hosts.deny ## ## ATTENTION! This is a map, not a list, even when we treat it as such. ## mod_rewrite parses it for key/value pairs, so at least a ## dummy value "-" must be present for each entry. ## 193.102.180.41 - bsdti1.sdm.de - 192.76.162.40 - </pre></div> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="proxy-deny" id="proxy-deny">Proxy Deny</a></h2> <dl> <dt>Description:</dt> <dd> <p>How can we forbid a certain host or even a user of a special host from using the Apache proxy?</p> </dd> <dt>Solution:</dt> <dd> <p>We first have to make sure <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> is below(!) <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code> in the Configuration file when compiling the Apache web server. This way it gets called <em>before</em> <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code>. Then we configure the following for a host-dependent deny...</p> <div class="example"><pre> RewriteCond %{REMOTE_HOST} <strong>^badhost\.mydomain\.com$</strong> RewriteRule !^http://[^/.]\.mydomain.com.* - [F] </pre></div> <p>...and this one for a user@host-dependent deny:</p> <div class="example"><pre> RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>^badguy@badhost\.mydomain\.com$</strong> RewriteRule !^http://[^/.]\.mydomain.com.* - [F] </pre></div> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="special-authentication" id="special-authentication">Special Authentication Variant</a></h2> <dl> <dt>Description:</dt> <dd> <p>Sometimes very special authentication is needed, for instance authentication which checks for a set of explicitly configured users. Only these should receive access and without explicit prompting (which would occur when using Basic Auth via <code class="module"><a href="../mod/mod_auth_basic.html">mod_auth_basic</a></code>).</p> </dd> <dt>Solution:</dt> <dd> <p>We use a list of rewrite conditions to exclude all except our friends:</p> <div class="example"><pre> RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>!^friend1@client1.quux-corp\.com$</strong> RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>!^friend2</strong>@client2.quux-corp\.com$ RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>!^friend3</strong>@client3.quux-corp\.com$ RewriteRule ^/~quux/only-for-friends/ - [F] </pre></div> </dd> </dl> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="referer-deflector" id="referer-deflector">Referer-based Deflector</a></h2> <dl> <dt>Description:</dt> <dd> <p>How can we program a flexible URL Deflector which acts on the "Referer" HTTP header and can be configured with as many referring pages as we like?</p> </dd> <dt>Solution:</dt> <dd> <p>Use the following really tricky ruleset...</p> <div class="example"><pre> RewriteMap deflector txt:/path/to/deflector.map RewriteCond %{HTTP_REFERER} !="" RewriteCond ${deflector:%{HTTP_REFERER}} ^-$ RewriteRule ^.* %{HTTP_REFERER} [R,L] RewriteCond %{HTTP_REFERER} !="" RewriteCond ${deflector:%{HTTP_REFERER}|NOT-FOUND} !=NOT-FOUND RewriteRule ^.* ${deflector:%{HTTP_REFERER}} [R,L] </pre></div> <p>... in conjunction with a corresponding rewrite map:</p> <div class="example"><pre> ## ## deflector.map ## http://www.badguys.com/bad/index.html - http://www.badguys.com/bad/index2.html - http://www.badguys.com/bad/index3.html http://somewhere.com/ </pre></div> <p>This automatically redirects the request back to the referring page (when "<code>-</code>" is used as the value in the map) or to a specific URL (when an URL is specified in the map as the second argument).</p> </dd> </dl> </div></div> <div class="bottomlang"> <p><span>Available Languages: </span><a href="../en/rewrite/rewrite_guide_advanced.html" title="English"> en </a></p> </div><div id="footer"> <p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p> <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div> </body></html>
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