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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/quickreference.html">Directives</a> | <a href="http://wiki.apache.org/httpd/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/advanced.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><ul class="seealso"><li><a href="#comments_section">Comments</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">
96 RewriteMap users-to-hosts txt:/path/to/map.users-to-hosts
97 RewriteRule ^/u/([^/]+)/?(.*) http://${users-to-hosts:$1|server0}/u/$1/$2
103 <p>See the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>
104 documentation for more discussion of the syntax of this directive.</p>
106 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
107 <div class="section">
108 <h2><a name="on-the-fly-content" id="on-the-fly-content">On-the-fly Content-Regeneration</a></h2>
113 <dt>Description:</dt>
116 <p>We wish to dynamically generate content, but store it
117 statically once it is generated. This rule will check for the
118 existence of the static file, and if it's not there, generate
119 it. The static files can be removed periodically, if desired (say,
120 via cron) and will be regenerated on demand.</p>
126 This is done via the following ruleset:
128 <pre class="prettyprint lang-config">
129 # This example is valid in per-directory context only
130 RewriteCond %{REQUEST_URI} !-U
131 RewriteRule ^(.+)\.html$ /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 <pre class="prettyprint lang-config">
172 RewriteMap lb rnd:/path/to/serverlist.txt
173 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 <pre class="prettyprint lang-config">
227 RewriteRule ^(/[uge]/[^/]+/?.*):refresh /internal/cgi/apache/nph-refresh?f=$1
231 <p>Now when we reference the URL</p>
233 <div class="example"><p><code>
234 /u/foo/bar/page.html:refresh
237 <p>this leads to the internal invocation of the URL</p>
239 <div class="example"><p><code>
240 /internal/cgi/apache/nph-refresh?f=/u/foo/bar/page.html
243 <p>The only missing part is the NPH-CGI script. Although
244 one would usually say "left as an exercise to the reader"
245 ;-) I will provide this, too.</p>
247 <pre class="prettyprint lang-perl">
250 ## nph-refresh -- NPH/CGI script for auto refreshing pages
251 ## Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved.
255 # split the QUERY_STRING variable
256 @pairs = split( /&/, $ENV{'QUERY_STRING'} );
257 foreach $pair (@pairs) {
258 ( $name, $value ) = split( /=/, $pair );
259 $name =~ tr/A-Z/a-z/;
260 $name = 'QS_' . $name;
261 $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg;
262 eval "\$$name = \"$value\"";
264 $QS_s = 1 if ( $QS_s eq '' );
265 $QS_n = 3600 if ( $QS_n eq '' );
267 print "HTTP/1.0 200 OK\n";
268 print "Content-type: text/html\n\n";
269 print "<b>ERROR</b>: No file given\n";
273 print "HTTP/1.0 200 OK\n";
274 print "Content-type: text/html\n\n";
275 print "<b>ERROR</b>: File $QS_f not found\n";
279 sub print_http_headers_multipart_begin {
280 print "HTTP/1.0 200 OK\n";
281 $bound = "ThisRandomString12345";
282 print "Content-type: multipart/x-mixed-replace;boundary=$bound\n";
283 &print_http_headers_multipart_next;
286 sub print_http_headers_multipart_next {
287 print "\n--$bound\n";
290 sub print_http_headers_multipart_end {
291 print "\n--$bound--\n";
295 local ($buffer) = @_;
296 $len = length($buffer);
297 print "Content-type: text/html\n";
298 print "Content-length: $len\n\n";
304 local ( *FP, $size, $buffer, $bytes );
305 ( $x, $x, $x, $x, $x, $x, $x, $size ) = stat($file);
306 $size = sprintf( "%d", $size );
307 open( FP, "<$file" );
308 $bytes = sysread( FP, $buffer, $size );
313 $buffer = &readfile($QS_f);
314 &print_http_headers_multipart_begin;
315 &displayhtml($buffer);
318 local ($file) = $_[0];
321 ( $x, $x, $x, $x, $x, $x, $x, $x, $x, $mtime ) = stat($file);
325 $mtimeL = &mystat($QS_f);
327 for ( $n = 0 ; $n & lt ; $QS_n ; $n++ ) {
329 $mtime = &mystat($QS_f);
330 if ( $mtime ne $mtimeL ) {
333 $buffer = &readfile($QS_f);
334 &print_http_headers_multipart_next;
335 &displayhtml($buffer);
337 $mtimeL = &mystat($QS_f);
344 &print_http_headers_multipart_end;
354 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
355 <div class="section">
356 <h2><a name="structuredhomedirs" id="structuredhomedirs">Structured Userdirs</a></h2>
361 <dt>Description:</dt>
364 <p>Some sites with thousands of users use a
365 structured homedir layout, <em>i.e.</em> each homedir is in a
366 subdirectory which begins (for instance) with the first
367 character of the username. So, <code>/~larry/anypath</code>
368 is <code>/home/<strong>l</strong>/larry/public_html/anypath</code>
369 while <code>/~waldo/anypath</code> is
370 <code>/home/<strong>w</strong>/waldo/public_html/anypath</code>.</p>
376 <p>We use the following ruleset to expand the tilde URLs
377 into the above layout.</p>
379 <pre class="prettyprint lang-config">
381 RewriteRule ^/~(<strong>([a-z])</strong>[a-z0-9]+)(.*) /home/<strong>$2</strong>/$1/public_html$3
387 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
388 <div class="section">
389 <h2><a name="redirectanchors" id="redirectanchors">Redirecting Anchors</a></h2>
394 <dt>Description:</dt>
397 <p>By default, redirecting to an HTML anchor doesn't work,
398 because mod_rewrite escapes the <code>#</code> character,
399 turning it into <code>%23</code>. This, in turn, breaks the
406 <p>Use the <code>[NE]</code> flag on the
407 <code>RewriteRule</code>. NE stands for No Escape.
412 <dd>This technique will of course also work with other
413 special characters that mod_rewrite, by default, URL-encodes.</dd>
416 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
417 <div class="section">
418 <h2><a name="time-dependent" id="time-dependent">Time-Dependent Rewriting</a></h2>
423 <dt>Description:</dt>
426 <p>We wish to use mod_rewrite to serve different content based on
433 <p>There are a lot of variables named <code>TIME_xxx</code>
434 for rewrite conditions. In conjunction with the special
435 lexicographic comparison patterns <code><STRING</code>,
436 <code>>STRING</code> and <code>=STRING</code> we can
437 do time-dependent redirects:</p>
439 <pre class="prettyprint lang-config">
441 RewriteCond %{TIME_HOUR}%{TIME_MIN} >0700
442 RewriteCond %{TIME_HOUR}%{TIME_MIN} <1900
443 RewriteRule ^foo\.html$ foo.day.html [L]
444 RewriteRule ^foo\.html$ foo.night.html
448 <p>This provides the content of <code>foo.day.html</code>
449 under the URL <code>foo.html</code> from
450 <code>07:01-18:59</code> and at the remaining time the
451 contents of <code>foo.night.html</code>.</p>
453 <div class="warning"><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>, intermediate proxies
454 and browsers may each cache responses and cause the either page to be
455 shown outside of the time-window configured.
456 <code class="module"><a href="../mod/mod_expires.html">mod_expires</a></code> may be used to control this
457 effect. You are, of course, much better off simply serving the
458 content dynamically, and customizing it based on the time of day.</div>
463 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
464 <div class="section">
465 <h2><a name="setenvvars" id="setenvvars">Set Environment Variables Based On URL Parts</a></h2>
470 <dt>Description:</dt>
473 <p>At time, we want to maintain some kind of status when we
474 perform a rewrite. For example, you want to make a note that
475 you've done that rewrite, so that you can check later to see if a
476 request can via that rewrite. One way to do this is by setting an
477 environment variable.</p>
483 <p>Use the [E] flag to set an environment variable.</p>
485 <pre class="prettyprint lang-config">
487 RewriteRule ^/horse/(.*) /pony/$1 [E=<strong>rewritten:1</strong>]
491 <p>Later in your ruleset you might check for this environment
492 variable using a RewriteCond:</p>
494 <pre class="prettyprint lang-config">
495 RewriteCond %{ENV:rewritten} =1
499 <p>Note that environment variables do not survive an external
500 redirect. You might consider using the [CO] flag to set a
507 <div class="bottomlang">
508 <p><span>Available Languages: </span><a href="../en/rewrite/advanced.html" title="English"> en </a></p>
509 </div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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