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8 <title>Advanced Techniques with mod_rewrite - Apache HTTP Server</title>
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17 <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>
18 <p class="apache">Apache HTTP Server Version 2.5</p>
19 <img alt="" src="../images/feather.gif" /></div>
20 <div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
22 <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>
24 <p><span>Available Languages: </span><a href="../en/rewrite/avoid.html" title="English"> en </a></p>
28 <p>This document supplements the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
29 <a href="../mod/mod_rewrite.html">reference documentation</a>. It provides
30 a few advanced techniques using mod_rewrite.</p>
32 <div class="warning">Note that many of these examples won't work unchanged in your
33 particular server configuration, so it's important that you understand
34 them, rather than merely cutting and pasting the examples into your
38 <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#sharding">URL-based sharding accross multiple backends</a></li>
39 <li><img alt="" src="../images/down.gif" /> <a href="#on-the-fly-content">On-the-fly Content-Regeneration</a></li>
40 <li><img alt="" src="../images/down.gif" /> <a href="#load-balancing">Load Balancing</a></li>
41 <li><img alt="" src="../images/down.gif" /> <a href="#autorefresh">Document With Autorefresh</a></li>
42 <li><img alt="" src="../images/down.gif" /> <a href="#structuredhomedirs">Structured Userdirs</a></li>
43 <li><img alt="" src="../images/down.gif" /> <a href="#redirectanchors">Redirecting Anchors</a></li>
44 <li><img alt="" src="../images/down.gif" /> <a href="#time-dependent">Time-Dependent Rewriting</a></li>
45 <li><img alt="" src="../images/down.gif" /> <a href="#setenvvars">Set Environment Variables Based On URL Parts</a></li>
46 </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>
47 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
49 <h2><a name="sharding" id="sharding">URL-based sharding accross multiple backends</a></h2>
57 <p>A common technique for distributing the burden of
58 server load or storage space is called "sharding".
59 When using this method, a front-end server will use the
60 url to consistently "shard" users or objects to separate
67 <p>A mapping is maintained, from users to target servers, in
68 external map files. They look like:</p>
70 <div class="example"><p><code>
71 user1 physical_host_of_user1<br />
72 user2 physical_host_of_user2<br />
76 <p>We put this into a <code>map.users-to-hosts</code> file. The
79 <div class="example"><p><code>
85 <div class="example"><p><code>
86 http://physical_host_of_user1/u/user/anypath
89 <p>thus every URL path need not be valid on every backend physical
90 host. The following ruleset does this for us with the help of the map
91 files assuming that server0 is a default server which will be used if
92 a user has no entry in the map:</p>
94 <div class="example"><p><code>
95 RewriteEngine on<br />
97 RewriteMap users-to-hosts txt:/path/to/map.users-to-hosts<br />
99 RewriteRule ^/u/<strong>([^/]+)</strong>/?(.*) http://<strong>${users-to-hosts:$1|server0}</strong>/u/$1/$2
104 <p>See the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>
105 documentation for more discussion of the syntax of this directive.</p>
107 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
108 <div class="section">
109 <h2><a name="on-the-fly-content" id="on-the-fly-content">On-the-fly Content-Regeneration</a></h2>
114 <dt>Description:</dt>
117 <p>We wish to dynamically generate content, but store it
118 statically once it is generated. This rule will check for the
119 existence of the static file, and if it's not there, generate
120 it. The static files can be removed periodically, if desired (say,
121 via cron) and will be regenerated on demand.</p>
127 This is done via the following ruleset:
129 <div class="example"><p><code>
130 # This example is valid in per-directory context only<br />
131 RewriteCond %{REQUEST_URI} <strong>!-U</strong><br />
132 RewriteRule ^(.+)\.html$ /regenerate_page.cgi [PT,L]
135 <p>The <code>-U</code> operator determines whether the test string
136 (in this case, <code>REQUEST_URI</code>) is a valid URL. It does
137 this via a subrequest. In the event that this subrequest fails -
138 that is, the requested resource doesn't exist - this rule invokes
139 the CGI program <code>/regenerate_page.cgi</code>, which generates
140 the requested resource and saves it into the document directory, so
141 that the next time it is requested, a static copy can be served.</p>
143 <p>In this way, documents that are infrequently updated can be served in
144 static form. if documents need to be refreshed, they can be deleted
145 from the document directory, and they will then be regenerated the
146 next time they are requested.</p>
150 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
151 <div class="section">
152 <h2><a name="load-balancing" id="load-balancing">Load Balancing</a></h2>
157 <dt>Description:</dt>
160 <p>We wish to randomly distribute load across several servers
161 using mod_rewrite.</p>
167 <p>We'll use <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> and a list of servers
168 to accomplish this.</p>
170 <div class="example"><p><code>
171 RewriteEngine on<br />
172 RewriteMap lb rnd:/path/to/serverlist.txt<br />
174 RewriteRule ^/(.*) http://${lb:servers}/$1 [P,L]
177 <p><code>serverlist.txt</code> will contain a list of the servers:</p>
179 <div class="example"><p><code>
180 ## serverlist.txt<br />
182 servers one.example.com|two.example.com|three.example.com<br />
185 <p>If you want one particular server to get more of the load than the
186 others, add it more times to the list.</p>
192 <p>Apache comes with a load-balancing module -
193 <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> - which is far more flexible and
194 featureful than anything you can cobble together using mod_rewrite.</p>
198 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
199 <div class="section">
200 <h2><a name="autorefresh" id="autorefresh">Document With Autorefresh</a></h2>
207 <dt>Description:</dt>
210 <p>Wouldn't it be nice, while creating a complex web page, if
211 the web browser would automatically refresh the page every
212 time we save a new version from within our editor?
219 <p>No! We just combine the MIME multipart feature, the
220 web server NPH feature, and the URL manipulation power of
221 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>. First, we establish a new
222 URL feature: Adding just <code>:refresh</code> to any
223 URL causes the 'page' to be refreshed every time it is
224 updated on the filesystem.</p>
226 <div class="example"><p><code>
227 RewriteRule ^(/[uge]/[^/]+/?.*):refresh /internal/cgi/apache/nph-refresh?f=$1
230 <p>Now when we reference the URL</p>
232 <div class="example"><p><code>
233 /u/foo/bar/page.html:refresh
236 <p>this leads to the internal invocation of the URL</p>
238 <div class="example"><p><code>
239 /internal/cgi/apache/nph-refresh?f=/u/foo/bar/page.html
242 <p>The only missing part is the NPH-CGI script. Although
243 one would usually say "left as an exercise to the reader"
244 ;-) I will provide this, too.</p>
246 <div class="example"><pre>
249 ## nph-refresh -- NPH/CGI script for auto refreshing pages
250 ## Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved.
254 # split the QUERY_STRING variable
255 @pairs = split(/&/, $ENV{'QUERY_STRING'});
256 foreach $pair (@pairs) {
257 ($name, $value) = split(/=/, $pair);
258 $name =~ tr/A-Z/a-z/;
259 $name = 'QS_' . $name;
260 $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg;
261 eval "\$$name = \"$value\"";
263 $QS_s = 1 if ($QS_s eq '');
264 $QS_n = 3600 if ($QS_n eq '');
266 print "HTTP/1.0 200 OK\n";
267 print "Content-type: text/html\n\n";
268 print "&lt;b&gt;ERROR&lt;/b&gt;: No file given\n";
272 print "HTTP/1.0 200 OK\n";
273 print "Content-type: text/html\n\n";
274 print "&lt;b&gt;ERROR&lt;/b&gt;: File $QS_f not found\n";
278 sub print_http_headers_multipart_begin {
279 print "HTTP/1.0 200 OK\n";
280 $bound = "ThisRandomString12345";
281 print "Content-type: multipart/x-mixed-replace;boundary=$bound\n";
282 &print_http_headers_multipart_next;
285 sub print_http_headers_multipart_next {
286 print "\n--$bound\n";
289 sub print_http_headers_multipart_end {
290 print "\n--$bound--\n";
295 $len = length($buffer);
296 print "Content-type: text/html\n";
297 print "Content-length: $len\n\n";
303 local(*FP, $size, $buffer, $bytes);
304 ($x, $x, $x, $x, $x, $x, $x, $size) = stat($file);
305 $size = sprintf("%d", $size);
306 open(FP, "&lt;$file");
307 $bytes = sysread(FP, $buffer, $size);
312 $buffer = &readfile($QS_f);
313 &print_http_headers_multipart_begin;
314 &displayhtml($buffer);
317 local($file) = $_[0];
320 ($x, $x, $x, $x, $x, $x, $x, $x, $x, $mtime) = stat($file);
324 $mtimeL = &mystat($QS_f);
326 for ($n = 0; $n &lt; $QS_n; $n++) {
328 $mtime = &mystat($QS_f);
329 if ($mtime ne $mtimeL) {
332 $buffer = &readfile($QS_f);
333 &print_http_headers_multipart_next;
334 &displayhtml($buffer);
336 $mtimeL = &mystat($QS_f);
343 &print_http_headers_multipart_end;
352 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
353 <div class="section">
354 <h2><a name="structuredhomedirs" id="structuredhomedirs">Structured Userdirs</a></h2>
359 <dt>Description:</dt>
362 <p>Some sites with thousands of users use a
363 structured homedir layout, <em>i.e.</em> each homedir is in a
364 subdirectory which begins (for instance) with the first
365 character of the username. So, <code>/~larry/anypath</code>
366 is <code>/home/<strong>l</strong>/larry/public_html/anypath</code>
367 while <code>/~waldo/anypath</code> is
368 <code>/home/<strong>w</strong>/waldo/public_html/anypath</code>.</p>
374 <p>We use the following ruleset to expand the tilde URLs
375 into the above layout.</p>
377 <div class="example"><p><code>
378 RewriteEngine on<br />
379 RewriteRule ^/~(<strong>([a-z])</strong>[a-z0-9]+)(.*) /home/<strong>$2</strong>/$1/public_html$3
384 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
385 <div class="section">
386 <h2><a name="redirectanchors" id="redirectanchors">Redirecting Anchors</a></h2>
391 <dt>Description:</dt>
394 <p>By default, redirecting to an HTML anchor doesn't work,
395 because mod_rewrite escapes the <code>#</code> character,
396 turning it into <code>%23</code>. This, in turn, breaks the
403 <p>Use the <code>[NE]</code> flag on the
404 <code>RewriteRule</code>. NE stands for No Escape.
409 <dd>This technique will of course also work with other
410 special characters that mod_rewrite, by default, URL-encodes.</dd>
413 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
414 <div class="section">
415 <h2><a name="time-dependent" id="time-dependent">Time-Dependent Rewriting</a></h2>
420 <dt>Description:</dt>
423 <p>We wish to use mod_rewrite to serve different content based on
430 <p>There are a lot of variables named <code>TIME_xxx</code>
431 for rewrite conditions. In conjunction with the special
432 lexicographic comparison patterns <code><STRING</code>,
433 <code>>STRING</code> and <code>=STRING</code> we can
434 do time-dependent redirects:</p>
436 <div class="example"><p><code>
437 RewriteEngine on<br />
438 RewriteCond %{TIME_HOUR}%{TIME_MIN} >0700<br />
439 RewriteCond %{TIME_HOUR}%{TIME_MIN} <1900<br />
440 RewriteRule ^foo\.html$ foo.day.html [L]<br />
441 RewriteRule ^foo\.html$ foo.night.html
444 <p>This provides the content of <code>foo.day.html</code>
445 under the URL <code>foo.html</code> from
446 <code>07:01-18:59</code> and at the remaining time the
447 contents of <code>foo.night.html</code>.</p>
449 <div class="warning"><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>, intermediate proxies
450 and browsers may each cache responses and cause the either page to be
451 shown outside of the time-window configured.
452 <code class="module"><a href="../mod/mod_expires.html">mod_expires</a></code> may be used to control this
453 effect. You are, of course, much better off simply serving the
454 content dynamically, and customizing it based on the time of day.</div>
459 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
460 <div class="section">
461 <h2><a name="setenvvars" id="setenvvars">Set Environment Variables Based On URL Parts</a></h2>
466 <dt>Description:</dt>
469 <p>At time, we want to maintain some kind of status when we
470 perform a rewrite. For example, you want to make a note that
471 you've done that rewrite, so that you can check later to see if a
472 request can via that rewrite. One way to do this is by setting an
473 environment variable.</p>
479 <p>Use the [E] flag to set an environment variable.</p>
481 <div class="example"><p><code>
482 RewriteEngine on<br />
483 RewriteRule ^/horse/(.*) /pony/$1 [E=<strong>rewritten:1</strong>]
486 <p>Later in your ruleset you might check for this environment
487 variable using a RewriteCond:</p>
489 <div class="example"><p><code>
490 RewriteCond %{ENV:rewritten} =1
493 <p>Note that environment variables do not survive an external
494 redirect. You might consider using the [CO] flag to set a
501 <div class="bottomlang">
502 <p><span>Available Languages: </span><a href="../en/rewrite/avoid.html" title="English"> en </a></p>
503 </div><div id="footer">
504 <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>
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