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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 2.3</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 2.3</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 and tricks 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">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"><pre>
68 user1 physical_host_of_user1
69 user2 physical_host_of_user2
73 <p>We put this into a <code>map.users-to-hosts</code> file. The
76 <div class="example"><pre>
82 <div class="example"><pre>
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"><pre>
94 RewriteMap users-to-hosts txt:/path/to/map.users-to-hosts
96 RewriteRule ^/u/<strong>([^/]+)</strong>/?(.*) http://<strong>${users-to-hosts:$1|server0}</strong>/u/$1/$2
101 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
102 <div class="section">
103 <h2><a name="on-the-fly-content" id="on-the-fly-content">On-the-fly Content-Regeneration</a></h2>
108 <dt>Description:</dt>
111 <p>We wish to dynamically generate content, but store it
112 statically once it is generated. This rule will check for the
113 existence of the static file, and if it's not there, generate
114 it. The static files can be removed periodically, if desired (say,
115 via cron) and will be regenerated on demand.</p>
121 This is done via the following ruleset:
123 <div class="example"><pre>
124 # This example is valid in per-directory context only
125 RewriteCond %{REQUEST_FILENAME} <strong>!-s</strong>
126 RewriteRule ^page\.<strong>html</strong>$ page.<strong>cgi</strong> [T=application/x-httpd-cgi,L]
129 <p>Here a request for <code>page.html</code> leads to an
130 internal run of a corresponding <code>page.cgi</code> if
131 <code>page.html</code> is missing or has filesize
132 null. The trick here is that <code>page.cgi</code> is a
133 CGI script which (additionally to its <code>STDOUT</code>)
134 writes its output to the file <code>page.html</code>.
135 Once it has completed, the server sends out
136 <code>page.html</code>. When the webmaster wants to force
137 a refresh of the contents, he just removes
138 <code>page.html</code> (typically from <code>cron</code>).</p>
142 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
143 <div class="section">
144 <h2><a name="load-balancing" id="load-balancing">Load Balancing</a></h2>
149 <dt>Description:</dt>
152 <p>We wish to randomly distribute load across several servers
153 using mod_rewrite.</p>
159 <p>We'll use <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> and a list of servers
160 to accomplish this.</p>
162 <div class="example"><pre>
164 RewriteMap lb rnd:/path/to/serverlist.txt
166 RewriteRule ^/(.*) http://${lb:servers}/$1 [P,L]
169 <p><code>serverlist.txt</code> will contain a list of the servers:</p>
171 <div class="example"><pre>
174 servers one.example.com|two.example.com|three.example.com
177 <p>If you want one particular server to get more of the load than the
178 others, add it more times to the list.</p>
184 <p>Apache comes with a load-balancing module -
185 <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> - which is far more flexible and
186 featureful than anything you can cobble together using mod_rewrite.</p>
190 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
191 <div class="section">
192 <h2><a name="autorefresh" id="autorefresh">Document With Autorefresh</a></h2>
197 <dt>Description:</dt>
200 <p>Wouldn't it be nice, while creating a complex web page, if
201 the web browser would automatically refresh the page every
202 time we save a new version from within our editor?
209 <p>No! We just combine the MIME multipart feature, the
210 web server NPH feature, and the URL manipulation power of
211 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>. First, we establish a new
212 URL feature: Adding just <code>:refresh</code> to any
213 URL causes the 'page' to be refreshed every time it is
214 updated on the filesystem.</p>
216 <div class="example"><pre>
217 RewriteRule ^(/[uge]/[^/]+/?.*):refresh /internal/cgi/apache/nph-refresh?f=$1
220 <p>Now when we reference the URL</p>
222 <div class="example"><pre>
223 /u/foo/bar/page.html:refresh
226 <p>this leads to the internal invocation of the URL</p>
228 <div class="example"><pre>
229 /internal/cgi/apache/nph-refresh?f=/u/foo/bar/page.html
232 <p>The only missing part is the NPH-CGI script. Although
233 one would usually say "left as an exercise to the reader"
234 ;-) I will provide this, too.</p>
236 <div class="example"><pre>
239 ## nph-refresh -- NPH/CGI script for auto refreshing pages
240 ## Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved.
244 # split the QUERY_STRING variable
245 @pairs = split(/&/, $ENV{'QUERY_STRING'});
246 foreach $pair (@pairs) {
247 ($name, $value) = split(/=/, $pair);
248 $name =~ tr/A-Z/a-z/;
249 $name = 'QS_' . $name;
250 $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg;
251 eval "\$$name = \"$value\"";
253 $QS_s = 1 if ($QS_s eq '');
254 $QS_n = 3600 if ($QS_n eq '');
256 print "HTTP/1.0 200 OK\n";
257 print "Content-type: text/html\n\n";
258 print "&lt;b&gt;ERROR&lt;/b&gt;: No file given\n";
262 print "HTTP/1.0 200 OK\n";
263 print "Content-type: text/html\n\n";
264 print "&lt;b&gt;ERROR&lt;/b&gt;: File $QS_f not found\n";
268 sub print_http_headers_multipart_begin {
269 print "HTTP/1.0 200 OK\n";
270 $bound = "ThisRandomString12345";
271 print "Content-type: multipart/x-mixed-replace;boundary=$bound\n";
272 &print_http_headers_multipart_next;
275 sub print_http_headers_multipart_next {
276 print "\n--$bound\n";
279 sub print_http_headers_multipart_end {
280 print "\n--$bound--\n";
285 $len = length($buffer);
286 print "Content-type: text/html\n";
287 print "Content-length: $len\n\n";
293 local(*FP, $size, $buffer, $bytes);
294 ($x, $x, $x, $x, $x, $x, $x, $size) = stat($file);
295 $size = sprintf("%d", $size);
296 open(FP, "&lt;$file");
297 $bytes = sysread(FP, $buffer, $size);
302 $buffer = &readfile($QS_f);
303 &print_http_headers_multipart_begin;
304 &displayhtml($buffer);
307 local($file) = $_[0];
310 ($x, $x, $x, $x, $x, $x, $x, $x, $x, $mtime) = stat($file);
314 $mtimeL = &mystat($QS_f);
316 for ($n = 0; $n &lt; $QS_n; $n++) {
318 $mtime = &mystat($QS_f);
319 if ($mtime ne $mtimeL) {
322 $buffer = &readfile($QS_f);
323 &print_http_headers_multipart_next;
324 &displayhtml($buffer);
326 $mtimeL = &mystat($QS_f);
333 &print_http_headers_multipart_end;
342 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
343 <div class="section">
344 <h2><a name="structuredhomedirs" id="structuredhomedirs">Structured Userdirs</a></h2>
349 <dt>Description:</dt>
352 <p>Some sites with thousands of users use a
353 structured homedir layout, <em>i.e.</em> each homedir is in a
354 subdirectory which begins (for instance) with the first
355 character of the username. So, <code>/~larry/anypath</code>
356 is <code>/home/<strong>l</strong>/larry/public_html/anypath</code>
357 while <code>/~waldo/anypath</code> is
358 <code>/home/<strong>w</strong>/waldo/public_html/anypath</code>.</p>
364 <p>We use the following ruleset to expand the tilde URLs
365 into the above layout.</p>
367 <div class="example"><pre>
369 RewriteRule ^/~(<strong>([a-z])</strong>[a-z0-9]+)(.*) /home/<strong>$2</strong>/$1/public_html$3
374 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
375 <div class="section">
376 <h2><a name="redirectanchors" id="redirectanchors">Redirecting Anchors</a></h2>
381 <dt>Description:</dt>
384 <p>By default, redirecting to an HTML anchor doesn't work,
385 because mod_rewrite escapes the <code>#</code> character,
386 turning it into <code>%23</code>. This, in turn, breaks the
393 <p>Use the <code>[NE]</code> flag on the
394 <code>RewriteRule</code>. NE stands for No Escape.
399 <dd>This technique will of course also work with other
400 special characters that mod_rewrite, by default, URL-encodes.</dd>
403 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
404 <div class="section">
405 <h2><a name="time-dependent" id="time-dependent">Time-Dependent Rewriting</a></h2>
410 <dt>Description:</dt>
413 <p>We wish to use mod_rewrite to serve different content based on
420 <p>There are a lot of variables named <code>TIME_xxx</code>
421 for rewrite conditions. In conjunction with the special
422 lexicographic comparison patterns <code><STRING</code>,
423 <code>>STRING</code> and <code>=STRING</code> we can
424 do time-dependent redirects:</p>
426 <div class="example"><pre>
428 RewriteCond %{TIME_HOUR}%{TIME_MIN} >0700
429 RewriteCond %{TIME_HOUR}%{TIME_MIN} <1900
430 RewriteRule ^foo\.html$ foo.day.html [L]
431 RewriteRule ^foo\.html$ foo.night.html
434 <p>This provides the content of <code>foo.day.html</code>
435 under the URL <code>foo.html</code> from
436 <code>07:01-18:59</code> and at the remaining time the
437 contents of <code>foo.night.html</code>.</p>
439 <div class="warning"><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>, intermediate proxies
440 and browsers may each cache responses and cause the either page to be
441 shown outside of the time-window configured.
442 <code class="module"><a href="../mod/mod_expires.html">mod_expires</a></code> may be used to control this
443 effect. You are, of course, much better off simply serving the
444 content dynamically, and customizing it based on the time of day.</div>
449 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
450 <div class="section">
451 <h2><a name="setenvvars" id="setenvvars">Set Environment Variables Based On URL Parts</a></h2>
456 <dt>Description:</dt>
459 <p>At time, we want to maintain some kind of status when we
460 perform a rewrite. For example, you want to make a note that
461 you've done that rewrite, so that you can check later to see if a
462 request can via that rewrite. One way to do this is by setting an
463 environment variable.</p>
469 <p>Use the [E] flag to set an environment variable.</p>
471 <div class="example"><pre>
473 RewriteRule ^/horse/(.*) /pony/$1 [E=<strong>rewritten:1</strong>]
476 <p>Later in your ruleset you might check for this environment
477 variable using a RewriteCond:</p>
479 <div class="example"><pre>
480 RewriteCond %{ENV:rewritten} =1
487 <div class="bottomlang">
488 <p><span>Available Languages: </span><a href="../en/rewrite/avoid.html" title="English"> en </a></p>
489 </div><div id="footer">
490 <p class="apache">Copyright 2010 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>
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