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8 <title>Advanced Techniques with mod_rewrite - Apache HTTP Server</title>
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14 <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>
15 <p class="apache">Apache HTTP Server Version 2.5</p>
16 <img alt="" src="../images/feather.gif" /></div>
17 <div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
19 <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 2.5</a> > <a href="./">Rewrite</a></div><div id="page-content"><div id="preamble"><h1>Advanced Techniques with mod_rewrite</h1>
21 <p><span>Available Languages: </span><a href="../en/rewrite/avoid.html" title="English"> en </a></p>
25 <p>This document supplements the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
26 <a href="../mod/mod_rewrite.html">reference documentation</a>. It provides
27 a few advanced techniques using mod_rewrite.</p>
29 <div class="warning">Note that many of these examples won't work unchanged in your
30 particular server configuration, so it's important that you understand
31 them, rather than merely cutting and pasting the examples into your
35 <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#sharding">URL-based sharding accross multiple backends</a></li>
36 <li><img alt="" src="../images/down.gif" /> <a href="#on-the-fly-content">On-the-fly Content-Regeneration</a></li>
37 <li><img alt="" src="../images/down.gif" /> <a href="#load-balancing">Load Balancing</a></li>
38 <li><img alt="" src="../images/down.gif" /> <a href="#autorefresh">Document With Autorefresh</a></li>
39 <li><img alt="" src="../images/down.gif" /> <a href="#structuredhomedirs">Structured Userdirs</a></li>
40 <li><img alt="" src="../images/down.gif" /> <a href="#redirectanchors">Redirecting Anchors</a></li>
41 <li><img alt="" src="../images/down.gif" /> <a href="#time-dependent">Time-Dependent Rewriting</a></li>
42 <li><img alt="" src="../images/down.gif" /> <a href="#setenvvars">Set Environment Variables Based On URL Parts</a></li>
43 </ul><h3>See also</h3><ul class="seealso"><li><a href="../mod/mod_rewrite.html">Module documentation</a></li><li><a href="intro.html">mod_rewrite introduction</a></li><li><a href="remapping.html">Redirection and remapping</a></li><li><a href="access.html">Controlling access</a></li><li><a href="vhosts.html">Virtual hosts</a></li><li><a href="proxy.html">Proxying</a></li><li><a href="rewritemap.html">Using RewriteMap</a></li><li><a href="avoid.html">When not to use mod_rewrite</a></li></ul></div>
44 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
46 <h2><a name="sharding" id="sharding">URL-based sharding accross multiple backends</a></h2>
54 <p>A common technique for distributing the burden of
55 server load or storage space is called "sharding".
56 When using this method, a front-end server will use the
57 url to consistently "shard" users or objects to separate
64 <p>A mapping is maintained, from users to target servers, in
65 external map files. They look like:</p>
67 <div class="example"><p><code>
68 user1 physical_host_of_user1<br />
69 user2 physical_host_of_user2<br />
73 <p>We put this into a <code>map.users-to-hosts</code> file. The
76 <div class="example"><p><code>
82 <div class="example"><p><code>
83 http://physical_host_of_user1/u/user/anypath
86 <p>thus every URL path need not be valid on every backend physical
87 host. The following ruleset does this for us with the help of the map
88 files assuming that server0 is a default server which will be used if
89 a user has no entry in the map:</p>
91 <div class="example"><p><code>
92 RewriteEngine on<br />
94 RewriteMap users-to-hosts txt:/path/to/map.users-to-hosts<br />
96 RewriteRule ^/u/<strong>([^/]+)</strong>/?(.*) http://<strong>${users-to-hosts:$1|server0}</strong>/u/$1/$2
101 <p>See the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>
102 documentation for more discussion of the syntax of this directive.</p>
104 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
105 <div class="section">
106 <h2><a name="on-the-fly-content" id="on-the-fly-content">On-the-fly Content-Regeneration</a></h2>
111 <dt>Description:</dt>
114 <p>We wish to dynamically generate content, but store it
115 statically once it is generated. This rule will check for the
116 existence of the static file, and if it's not there, generate
117 it. The static files can be removed periodically, if desired (say,
118 via cron) and will be regenerated on demand.</p>
124 This is done via the following ruleset:
126 <div class="example"><p><code>
127 # This example is valid in per-directory context only<br />
128 RewriteCond %{REQUEST_URI} <strong>!-U</strong><br />
129 RewriteRule ^(.+)\.html$ /regenerate_page.cgi [PT,L]
132 <p>The <code>-U</code> operator determines whether the test string
133 (in this case, <code>REQUEST_URI</code>) is a valid URL. It does
134 this via a subrequest. In the event that this subrequest fails -
135 that is, the requested resource doesn't exist - this rule invokes
136 the CGI program <code>/regenerate_page.cgi</code>, which generates
137 the requested resource and saves it into the document directory, so
138 that the next time it is requested, a static copy can be served.</p>
140 <p>In this way, documents that are infrequently updated can be served in
141 static form. if documents need to be refreshed, they can be deleted
142 from the document directory, and they will then be regenerated the
143 next time they are requested.</p>
147 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
148 <div class="section">
149 <h2><a name="load-balancing" id="load-balancing">Load Balancing</a></h2>
154 <dt>Description:</dt>
157 <p>We wish to randomly distribute load across several servers
158 using mod_rewrite.</p>
164 <p>We'll use <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> and a list of servers
165 to accomplish this.</p>
167 <div class="example"><p><code>
168 RewriteEngine on<br />
169 RewriteMap lb rnd:/path/to/serverlist.txt<br />
171 RewriteRule ^/(.*) http://${lb:servers}/$1 [P,L]
174 <p><code>serverlist.txt</code> will contain a list of the servers:</p>
176 <div class="example"><p><code>
177 ## serverlist.txt<br />
179 servers one.example.com|two.example.com|three.example.com<br />
182 <p>If you want one particular server to get more of the load than the
183 others, add it more times to the list.</p>
189 <p>Apache comes with a load-balancing module -
190 <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> - which is far more flexible and
191 featureful than anything you can cobble together using mod_rewrite.</p>
195 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
196 <div class="section">
197 <h2><a name="autorefresh" id="autorefresh">Document With Autorefresh</a></h2>
204 <dt>Description:</dt>
207 <p>Wouldn't it be nice, while creating a complex web page, if
208 the web browser would automatically refresh the page every
209 time we save a new version from within our editor?
216 <p>No! We just combine the MIME multipart feature, the
217 web server NPH feature, and the URL manipulation power of
218 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>. First, we establish a new
219 URL feature: Adding just <code>:refresh</code> to any
220 URL causes the 'page' to be refreshed every time it is
221 updated on the filesystem.</p>
223 <div class="example"><p><code>
224 RewriteRule ^(/[uge]/[^/]+/?.*):refresh /internal/cgi/apache/nph-refresh?f=$1
227 <p>Now when we reference the URL</p>
229 <div class="example"><p><code>
230 /u/foo/bar/page.html:refresh
233 <p>this leads to the internal invocation of the URL</p>
235 <div class="example"><p><code>
236 /internal/cgi/apache/nph-refresh?f=/u/foo/bar/page.html
239 <p>The only missing part is the NPH-CGI script. Although
240 one would usually say "left as an exercise to the reader"
241 ;-) I will provide this, too.</p>
243 <div class="example"><pre>
246 ## nph-refresh -- NPH/CGI script for auto refreshing pages
247 ## Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved.
251 # split the QUERY_STRING variable
252 @pairs = split(/&/, $ENV{'QUERY_STRING'});
253 foreach $pair (@pairs) {
254 ($name, $value) = split(/=/, $pair);
255 $name =~ tr/A-Z/a-z/;
256 $name = 'QS_' . $name;
257 $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg;
258 eval "\$$name = \"$value\"";
260 $QS_s = 1 if ($QS_s eq '');
261 $QS_n = 3600 if ($QS_n eq '');
263 print "HTTP/1.0 200 OK\n";
264 print "Content-type: text/html\n\n";
265 print "&lt;b&gt;ERROR&lt;/b&gt;: No file given\n";
269 print "HTTP/1.0 200 OK\n";
270 print "Content-type: text/html\n\n";
271 print "&lt;b&gt;ERROR&lt;/b&gt;: File $QS_f not found\n";
275 sub print_http_headers_multipart_begin {
276 print "HTTP/1.0 200 OK\n";
277 $bound = "ThisRandomString12345";
278 print "Content-type: multipart/x-mixed-replace;boundary=$bound\n";
279 &print_http_headers_multipart_next;
282 sub print_http_headers_multipart_next {
283 print "\n--$bound\n";
286 sub print_http_headers_multipart_end {
287 print "\n--$bound--\n";
292 $len = length($buffer);
293 print "Content-type: text/html\n";
294 print "Content-length: $len\n\n";
300 local(*FP, $size, $buffer, $bytes);
301 ($x, $x, $x, $x, $x, $x, $x, $size) = stat($file);
302 $size = sprintf("%d", $size);
303 open(FP, "&lt;$file");
304 $bytes = sysread(FP, $buffer, $size);
309 $buffer = &readfile($QS_f);
310 &print_http_headers_multipart_begin;
311 &displayhtml($buffer);
314 local($file) = $_[0];
317 ($x, $x, $x, $x, $x, $x, $x, $x, $x, $mtime) = stat($file);
321 $mtimeL = &mystat($QS_f);
323 for ($n = 0; $n &lt; $QS_n; $n++) {
325 $mtime = &mystat($QS_f);
326 if ($mtime ne $mtimeL) {
329 $buffer = &readfile($QS_f);
330 &print_http_headers_multipart_next;
331 &displayhtml($buffer);
333 $mtimeL = &mystat($QS_f);
340 &print_http_headers_multipart_end;
349 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
350 <div class="section">
351 <h2><a name="structuredhomedirs" id="structuredhomedirs">Structured Userdirs</a></h2>
356 <dt>Description:</dt>
359 <p>Some sites with thousands of users use a
360 structured homedir layout, <em>i.e.</em> each homedir is in a
361 subdirectory which begins (for instance) with the first
362 character of the username. So, <code>/~larry/anypath</code>
363 is <code>/home/<strong>l</strong>/larry/public_html/anypath</code>
364 while <code>/~waldo/anypath</code> is
365 <code>/home/<strong>w</strong>/waldo/public_html/anypath</code>.</p>
371 <p>We use the following ruleset to expand the tilde URLs
372 into the above layout.</p>
374 <div class="example"><p><code>
375 RewriteEngine on<br />
376 RewriteRule ^/~(<strong>([a-z])</strong>[a-z0-9]+)(.*) /home/<strong>$2</strong>/$1/public_html$3
381 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
382 <div class="section">
383 <h2><a name="redirectanchors" id="redirectanchors">Redirecting Anchors</a></h2>
388 <dt>Description:</dt>
391 <p>By default, redirecting to an HTML anchor doesn't work,
392 because mod_rewrite escapes the <code>#</code> character,
393 turning it into <code>%23</code>. This, in turn, breaks the
400 <p>Use the <code>[NE]</code> flag on the
401 <code>RewriteRule</code>. NE stands for No Escape.
406 <dd>This technique will of course also work with other
407 special characters that mod_rewrite, by default, URL-encodes.</dd>
410 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
411 <div class="section">
412 <h2><a name="time-dependent" id="time-dependent">Time-Dependent Rewriting</a></h2>
417 <dt>Description:</dt>
420 <p>We wish to use mod_rewrite to serve different content based on
427 <p>There are a lot of variables named <code>TIME_xxx</code>
428 for rewrite conditions. In conjunction with the special
429 lexicographic comparison patterns <code><STRING</code>,
430 <code>>STRING</code> and <code>=STRING</code> we can
431 do time-dependent redirects:</p>
433 <div class="example"><p><code>
434 RewriteEngine on<br />
435 RewriteCond %{TIME_HOUR}%{TIME_MIN} >0700<br />
436 RewriteCond %{TIME_HOUR}%{TIME_MIN} <1900<br />
437 RewriteRule ^foo\.html$ foo.day.html [L]<br />
438 RewriteRule ^foo\.html$ foo.night.html
441 <p>This provides the content of <code>foo.day.html</code>
442 under the URL <code>foo.html</code> from
443 <code>07:01-18:59</code> and at the remaining time the
444 contents of <code>foo.night.html</code>.</p>
446 <div class="warning"><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>, intermediate proxies
447 and browsers may each cache responses and cause the either page to be
448 shown outside of the time-window configured.
449 <code class="module"><a href="../mod/mod_expires.html">mod_expires</a></code> may be used to control this
450 effect. You are, of course, much better off simply serving the
451 content dynamically, and customizing it based on the time of day.</div>
456 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
457 <div class="section">
458 <h2><a name="setenvvars" id="setenvvars">Set Environment Variables Based On URL Parts</a></h2>
463 <dt>Description:</dt>
466 <p>At time, we want to maintain some kind of status when we
467 perform a rewrite. For example, you want to make a note that
468 you've done that rewrite, so that you can check later to see if a
469 request can via that rewrite. One way to do this is by setting an
470 environment variable.</p>
476 <p>Use the [E] flag to set an environment variable.</p>
478 <div class="example"><p><code>
479 RewriteEngine on<br />
480 RewriteRule ^/horse/(.*) /pony/$1 [E=<strong>rewritten:1</strong>]
483 <p>Later in your ruleset you might check for this environment
484 variable using a RewriteCond:</p>
486 <div class="example"><p><code>
487 RewriteCond %{ENV:rewritten} =1
490 <p>Note that environment variables do not survive an external
491 redirect. You might consider using the [CO] flag to set a
498 <div class="bottomlang">
499 <p><span>Available Languages: </span><a href="../en/rewrite/avoid.html" title="English"> en </a></p>
500 </div><div id="footer">
501 <p class="apache">Copyright 2012 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>
502 <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>