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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 <pre class="prettyprint lang-config">
97 RewriteMap users-to-hosts txt:/path/to/map.users-to-hosts
99 RewriteRule ^/u/<strong>([^/]+)</strong>/?(.*) http://<strong>${users-to-hosts:$1|server0}</strong>/u/$1/$2
105 <p>See the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>
106 documentation for more discussion of the syntax of this directive.</p>
108 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
109 <div class="section">
110 <h2><a name="on-the-fly-content" id="on-the-fly-content">On-the-fly Content-Regeneration</a></h2>
115 <dt>Description:</dt>
118 <p>We wish to dynamically generate content, but store it
119 statically once it is generated. This rule will check for the
120 existence of the static file, and if it's not there, generate
121 it. The static files can be removed periodically, if desired (say,
122 via cron) and will be regenerated on demand.</p>
128 This is done via the following ruleset:
130 <pre class="prettyprint lang-config">
131 # This example is valid in per-directory context only
132 RewriteCond %{REQUEST_URI} <strong>!-U</strong>
133 RewriteRule ^(.+)\.html$ /regenerate_page.cgi [PT,L]
137 <p>The <code>-U</code> operator determines whether the test string
138 (in this case, <code>REQUEST_URI</code>) is a valid URL. It does
139 this via a subrequest. In the event that this subrequest fails -
140 that is, the requested resource doesn't exist - this rule invokes
141 the CGI program <code>/regenerate_page.cgi</code>, which generates
142 the requested resource and saves it into the document directory, so
143 that the next time it is requested, a static copy can be served.</p>
145 <p>In this way, documents that are infrequently updated can be served in
146 static form. if documents need to be refreshed, they can be deleted
147 from the document directory, and they will then be regenerated the
148 next time they are requested.</p>
152 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
153 <div class="section">
154 <h2><a name="load-balancing" id="load-balancing">Load Balancing</a></h2>
159 <dt>Description:</dt>
162 <p>We wish to randomly distribute load across several servers
163 using mod_rewrite.</p>
169 <p>We'll use <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> and a list of servers
170 to accomplish this.</p>
172 <pre class="prettyprint lang-config">
174 RewriteMap lb rnd:/path/to/serverlist.txt
176 RewriteRule ^/(.*) http://${lb:servers}/$1 [P,L]
180 <p><code>serverlist.txt</code> will contain a list of the servers:</p>
182 <div class="example"><p><code>
183 ## serverlist.txt<br />
185 servers one.example.com|two.example.com|three.example.com<br />
188 <p>If you want one particular server to get more of the load than the
189 others, add it more times to the list.</p>
195 <p>Apache comes with a load-balancing module -
196 <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> - which is far more flexible and
197 featureful than anything you can cobble together using mod_rewrite.</p>
201 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
202 <div class="section">
203 <h2><a name="autorefresh" id="autorefresh">Document With Autorefresh</a></h2>
210 <dt>Description:</dt>
213 <p>Wouldn't it be nice, while creating a complex web page, if
214 the web browser would automatically refresh the page every
215 time we save a new version from within our editor?
222 <p>No! We just combine the MIME multipart feature, the
223 web server NPH feature, and the URL manipulation power of
224 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>. First, we establish a new
225 URL feature: Adding just <code>:refresh</code> to any
226 URL causes the 'page' to be refreshed every time it is
227 updated on the filesystem.</p>
229 <pre class="prettyprint lang-config">
230 RewriteRule ^(/[uge]/[^/]+/?.*):refresh /internal/cgi/apache/nph-refresh?f=$1
234 <p>Now when we reference the URL</p>
236 <div class="example"><p><code>
237 /u/foo/bar/page.html:refresh
240 <p>this leads to the internal invocation of the URL</p>
242 <div class="example"><p><code>
243 /internal/cgi/apache/nph-refresh?f=/u/foo/bar/page.html
246 <p>The only missing part is the NPH-CGI script. Although
247 one would usually say "left as an exercise to the reader"
248 ;-) I will provide this, too.</p>
250 <pre class="prettyprint lang-perl">
253 ## nph-refresh -- NPH/CGI script for auto refreshing pages
254 ## Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved.
258 # split the QUERY_STRING variable
259 @pairs = split(/&/, $ENV{'QUERY_STRING'});
260 foreach $pair (@pairs) {
261 ($name, $value) = split(/=/, $pair);
262 $name =~ tr/A-Z/a-z/;
263 $name = 'QS_' . $name;
264 $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg;
265 eval "\$$name = \"$value\"";
267 $QS_s = 1 if ($QS_s eq '');
268 $QS_n = 3600 if ($QS_n eq '');
270 print "HTTP/1.0 200 OK\n";
271 print "Content-type: text/html\n\n";
272 print "<b>ERROR</b>: No file given\n";
276 print "HTTP/1.0 200 OK\n";
277 print "Content-type: text/html\n\n";
278 print "<b>ERROR</b>: File $QS_f not found\n";
282 sub print_http_headers_multipart_begin {
283 print "HTTP/1.0 200 OK\n";
284 $bound = "ThisRandomString12345";
285 print "Content-type: multipart/x-mixed-replace;boundary=$bound\n";
286 &print_http_headers_multipart_next;
289 sub print_http_headers_multipart_next {
290 print "\n--$bound\n";
293 sub print_http_headers_multipart_end {
294 print "\n--$bound--\n";
299 $len = length($buffer);
300 print "Content-type: text/html\n";
301 print "Content-length: $len\n\n";
307 local(*FP, $size, $buffer, $bytes);
308 ($x, $x, $x, $x, $x, $x, $x, $size) = stat($file);
309 $size = sprintf("%d", $size);
310 open(FP, "<$file");
311 $bytes = sysread(FP, $buffer, $size);
316 $buffer = &readfile($QS_f);
317 &print_http_headers_multipart_begin;
318 &displayhtml($buffer);
321 local($file) = $_[0];
324 ($x, $x, $x, $x, $x, $x, $x, $x, $x, $mtime) = stat($file);
328 $mtimeL = &mystat($QS_f);
330 for ($n = 0; $n &lt; $QS_n; $n++) {
332 $mtime = &mystat($QS_f);
333 if ($mtime ne $mtimeL) {
336 $buffer = &readfile($QS_f);
337 &print_http_headers_multipart_next;
338 &displayhtml($buffer);
340 $mtimeL = &mystat($QS_f);
347 &print_http_headers_multipart_end;
357 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
358 <div class="section">
359 <h2><a name="structuredhomedirs" id="structuredhomedirs">Structured Userdirs</a></h2>
364 <dt>Description:</dt>
367 <p>Some sites with thousands of users use a
368 structured homedir layout, <em>i.e.</em> each homedir is in a
369 subdirectory which begins (for instance) with the first
370 character of the username. So, <code>/~larry/anypath</code>
371 is <code>/home/<strong>l</strong>/larry/public_html/anypath</code>
372 while <code>/~waldo/anypath</code> is
373 <code>/home/<strong>w</strong>/waldo/public_html/anypath</code>.</p>
379 <p>We use the following ruleset to expand the tilde URLs
380 into the above layout.</p>
382 <pre class="prettyprint lang-config">
384 RewriteRule ^/~(<strong>([a-z])</strong>[a-z0-9]+)(.*) /home/<strong>$2</strong>/$1/public_html$3
390 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
391 <div class="section">
392 <h2><a name="redirectanchors" id="redirectanchors">Redirecting Anchors</a></h2>
397 <dt>Description:</dt>
400 <p>By default, redirecting to an HTML anchor doesn't work,
401 because mod_rewrite escapes the <code>#</code> character,
402 turning it into <code>%23</code>. This, in turn, breaks the
409 <p>Use the <code>[NE]</code> flag on the
410 <code>RewriteRule</code>. NE stands for No Escape.
415 <dd>This technique will of course also work with other
416 special characters that mod_rewrite, by default, URL-encodes.</dd>
419 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
420 <div class="section">
421 <h2><a name="time-dependent" id="time-dependent">Time-Dependent Rewriting</a></h2>
426 <dt>Description:</dt>
429 <p>We wish to use mod_rewrite to serve different content based on
436 <p>There are a lot of variables named <code>TIME_xxx</code>
437 for rewrite conditions. In conjunction with the special
438 lexicographic comparison patterns <code><STRING</code>,
439 <code>>STRING</code> and <code>=STRING</code> we can
440 do time-dependent redirects:</p>
442 <pre class="prettyprint lang-config">
444 RewriteCond %{TIME_HOUR}%{TIME_MIN} >0700
445 RewriteCond %{TIME_HOUR}%{TIME_MIN} <1900
446 RewriteRule ^foo\.html$ foo.day.html [L]
447 RewriteRule ^foo\.html$ foo.night.html
451 <p>This provides the content of <code>foo.day.html</code>
452 under the URL <code>foo.html</code> from
453 <code>07:01-18:59</code> and at the remaining time the
454 contents of <code>foo.night.html</code>.</p>
456 <div class="warning"><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>, intermediate proxies
457 and browsers may each cache responses and cause the either page to be
458 shown outside of the time-window configured.
459 <code class="module"><a href="../mod/mod_expires.html">mod_expires</a></code> may be used to control this
460 effect. You are, of course, much better off simply serving the
461 content dynamically, and customizing it based on the time of day.</div>
466 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
467 <div class="section">
468 <h2><a name="setenvvars" id="setenvvars">Set Environment Variables Based On URL Parts</a></h2>
473 <dt>Description:</dt>
476 <p>At time, we want to maintain some kind of status when we
477 perform a rewrite. For example, you want to make a note that
478 you've done that rewrite, so that you can check later to see if a
479 request can via that rewrite. One way to do this is by setting an
480 environment variable.</p>
486 <p>Use the [E] flag to set an environment variable.</p>
488 <pre class="prettyprint lang-config">
490 RewriteRule ^/horse/(.*) /pony/$1 [E=<strong>rewritten:1</strong>]
494 <p>Later in your ruleset you might check for this environment
495 variable using a RewriteCond:</p>
497 <pre class="prettyprint lang-config">
498 RewriteCond %{ENV:rewritten} =1
502 <p>Note that environment variables do not survive an external
503 redirect. You might consider using the [CO] flag to set a
510 <div class="bottomlang">
511 <p><span>Available Languages: </span><a href="../en/rewrite/avoid.html" title="English"> en </a></p>
512 </div><div id="footer">
513 <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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