1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
|
<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head>
<meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type" />
<!--
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
This file is generated from xml source: DO NOT EDIT
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
-->
<title>Advanced Techniques with mod_rewrite - Apache HTTP Server Version 2.5</title>
<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
<link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link rel="stylesheet" type="text/css" href="../style/css/prettify.css" />
<script src="../style/scripts/prettify.min.js" type="text/javascript">
</script>
<link href="../images/favicon.ico" rel="shortcut icon" /></head>
<body id="manual-page"><div id="page-header">
<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>
<p class="apache">Apache HTTP Server Version 2.5</p>
<img alt="" src="../images/feather.png" /></div>
<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
<div id="path">
<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>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/rewrite/advanced.html" title="English"> en </a> |
<a href="../fr/rewrite/advanced.html" hreflang="fr" rel="alternate" title="Fran�ais"> fr </a></p>
</div>
<p>This document supplements the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
<a href="../mod/mod_rewrite.html">reference documentation</a>. It provides
a few advanced techniques using mod_rewrite.</p>
<div class="warning">Note that many of these examples won't work unchanged in your
particular server configuration, so it's important that you understand
them, rather than merely cutting and pasting the examples into your
configuration.</div>
</div>
<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#sharding">URL-based sharding across multiple backends</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#on-the-fly-content">On-the-fly Content-Regeneration</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#load-balancing">Load Balancing</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#structuredhomedirs">Structured Userdirs</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#redirectanchors">Redirecting Anchors</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#time-dependent">Time-Dependent Rewriting</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#setenvvars">Set Environment Variables Based On URL Parts</a></li>
</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><li><a href="#comments_section">Comments</a></li></ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="sharding" id="sharding">URL-based sharding across multiple backends</a> <a title="Permanent link" href="#sharding" class="permalink">¶</a></h2>
<dl>
<dt>Description:</dt>
<dd>
<p>A common technique for distributing the burden of
server load or storage space is called "sharding".
When using this method, a front-end server will use the
url to consistently "shard" users or objects to separate
backend servers.</p>
</dd>
<dt>Solution:</dt>
<dd>
<p>A mapping is maintained, from users to target servers, in
external map files. They look like:</p>
<div class="example"><p><code>
user1 physical_host_of_user1<br />
user2 physical_host_of_user2<br />
: :
</code></p></div>
<p>We put this into a <code>map.users-to-hosts</code> file. The
aim is to map;</p>
<div class="example"><p><code>
/u/user1/anypath
</code></p></div>
<p>to</p>
<div class="example"><p><code>
http://physical_host_of_user1/u/user/anypath
</code></p></div>
<p>thus every URL path need not be valid on every backend physical
host. The following ruleset does this for us with the help of the map
files assuming that server0 is a default server which will be used if
a user has no entry in the map:</p>
<pre class="prettyprint lang-config">RewriteEngine on
RewriteMap users-to-hosts "txt:/path/to/map.users-to-hosts"
RewriteRule "^/u/([^/]+)/?(.*)" "http://${users-to-hosts:$1|server0}/u/$1/$2"</pre>
</dd>
</dl>
<p>See the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>
documentation for more discussion of the syntax of this directive.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="on-the-fly-content" id="on-the-fly-content">On-the-fly Content-Regeneration</a> <a title="Permanent link" href="#on-the-fly-content" class="permalink">¶</a></h2>
<dl>
<dt>Description:</dt>
<dd>
<p>We wish to dynamically generate content, but store it
statically once it is generated. This rule will check for the
existence of the static file, and if it's not there, generate
it. The static files can be removed periodically, if desired (say,
via cron) and will be regenerated on demand.</p>
</dd>
<dt>Solution:</dt>
<dd>
This is done via the following ruleset:
<pre class="prettyprint lang-config"># This example is valid in per-directory context only
RewriteCond "%{REQUEST_URI}" !-U
RewriteRule "^(.+)\.html$" "/regenerate_page.cgi" [PT,L]</pre>
<p>The <code>-U</code> operator determines whether the test string
(in this case, <code>REQUEST_URI</code>) is a valid URL. It does
this via a subrequest. In the event that this subrequest fails -
that is, the requested resource doesn't exist - this rule invokes
the CGI program <code>/regenerate_page.cgi</code>, which generates
the requested resource and saves it into the document directory, so
that the next time it is requested, a static copy can be served.</p>
<p>In this way, documents that are infrequently updated can be served in
static form. if documents need to be refreshed, they can be deleted
from the document directory, and they will then be regenerated the
next time they are requested.</p>
</dd>
</dl>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="load-balancing" id="load-balancing">Load Balancing</a> <a title="Permanent link" href="#load-balancing" class="permalink">¶</a></h2>
<dl>
<dt>Description:</dt>
<dd>
<p>We wish to randomly distribute load across several servers
using mod_rewrite.</p>
</dd>
<dt>Solution:</dt>
<dd>
<p>We'll use <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> and a list of servers
to accomplish this.</p>
<pre class="prettyprint lang-config">RewriteEngine on
RewriteMap lb "rnd:/path/to/serverlist.txt"
RewriteRule "^/(.*)" "http://${lb:servers}/$1" [P,L]</pre>
<p><code>serverlist.txt</code> will contain a list of the servers:</p>
<div class="example"><p><code>
## serverlist.txt<br />
<br />
servers one.example.com|two.example.com|three.example.com<br />
</code></p></div>
<p>If you want one particular server to get more of the load than the
others, add it more times to the list.</p>
</dd>
<dt>Discussion</dt>
<dd>
<p>Apache comes with a load-balancing module -
<code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> - which is far more flexible and
featureful than anything you can cobble together using mod_rewrite.</p>
</dd>
</dl>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="structuredhomedirs" id="structuredhomedirs">Structured Userdirs</a> <a title="Permanent link" href="#structuredhomedirs" class="permalink">¶</a></h2>
<dl>
<dt>Description:</dt>
<dd>
<p>Some sites with thousands of users use a
structured homedir layout, <em>i.e.</em> each homedir is in a
subdirectory which begins (for instance) with the first
character of the username. So, <code>/~larry/anypath</code>
is <code>/home/<strong>l</strong>/larry/public_html/anypath</code>
while <code>/~waldo/anypath</code> is
<code>/home/<strong>w</strong>/waldo/public_html/anypath</code>.</p>
</dd>
<dt>Solution:</dt>
<dd>
<p>We use the following ruleset to expand the tilde URLs
into the above layout.</p>
<pre class="prettyprint lang-config">RewriteEngine on
RewriteRule "^/~(<strong>([a-z])</strong>[a-z0-9]+)(.*)" "/home/<strong>$2</strong>/$1/public_html$3"</pre>
</dd>
</dl>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="redirectanchors" id="redirectanchors">Redirecting Anchors</a> <a title="Permanent link" href="#redirectanchors" class="permalink">¶</a></h2>
<dl>
<dt>Description:</dt>
<dd>
<p>By default, redirecting to an HTML anchor doesn't work,
because mod_rewrite escapes the <code>#</code> character,
turning it into <code>%23</code>. This, in turn, breaks the
redirection.</p>
</dd>
<dt>Solution:</dt>
<dd>
<p>Use the <code>[NE]</code> flag on the
<code>RewriteRule</code>. NE stands for No Escape.
</p>
</dd>
<dt>Discussion:</dt>
<dd>This technique will of course also work with other
special characters that mod_rewrite, by default, URL-encodes.</dd>
</dl>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="time-dependent" id="time-dependent">Time-Dependent Rewriting</a> <a title="Permanent link" href="#time-dependent" class="permalink">¶</a></h2>
<dl>
<dt>Description:</dt>
<dd>
<p>We wish to use mod_rewrite to serve different content based on
the time of day.</p>
</dd>
<dt>Solution:</dt>
<dd>
<p>There are a lot of variables named <code>TIME_xxx</code>
for rewrite conditions. In conjunction with the special
lexicographic comparison patterns <code><STRING</code>,
<code>>STRING</code> and <code>=STRING</code> we can
do time-dependent redirects:</p>
<pre class="prettyprint lang-config">RewriteEngine on
RewriteCond "%{TIME_HOUR}%{TIME_MIN}" >0700
RewriteCond "%{TIME_HOUR}%{TIME_MIN}" <1900
RewriteRule "^foo\.html$" "foo.day.html" [L]
RewriteRule "^foo\.html$" "foo.night.html"</pre>
<p>This provides the content of <code>foo.day.html</code>
under the URL <code>foo.html</code> from
<code>07:01-18:59</code> and at the remaining time the
contents of <code>foo.night.html</code>.</p>
<div class="warning"><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>, intermediate proxies
and browsers may each cache responses and cause the either page to be
shown outside of the time-window configured.
<code class="module"><a href="../mod/mod_expires.html">mod_expires</a></code> may be used to control this
effect. You are, of course, much better off simply serving the
content dynamically, and customizing it based on the time of day.</div>
</dd>
</dl>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="setenvvars" id="setenvvars">Set Environment Variables Based On URL Parts</a> <a title="Permanent link" href="#setenvvars" class="permalink">¶</a></h2>
<dl>
<dt>Description:</dt>
<dd>
<p>At times, we want to maintain some kind of status when we
perform a rewrite. For example, you want to make a note that
you've done that rewrite, so that you can check later to see if a
request came via that rewrite. One way to do this is by setting an
environment variable.</p>
</dd>
<dt>Solution:</dt>
<dd>
<p>Use the [E] flag to set an environment variable.</p>
<pre class="prettyprint lang-config">RewriteEngine on
RewriteRule "^/horse/(.*)" "/pony/$1" [E=<strong>rewritten:1</strong>]</pre>
<p>Later in your ruleset you might check for this environment
variable using a RewriteCond:</p>
<pre class="prettyprint lang-config">RewriteCond "%{ENV:rewritten}" =1</pre>
<p>Note that environment variables do not survive an external
redirect. You might consider using the [CO] flag to set a
cookie. For per-directory and htaccess rewrites, where the final
substitution is processed as an internal redirect, environment
variables from the previous round of rewriting are prefixed with
"REDIRECT_". </p>
</dd>
</dl>
</div></div>
<div class="bottomlang">
<p><span>Available Languages: </span><a href="../en/rewrite/advanced.html" title="English"> en </a> |
<a href="../fr/rewrite/advanced.html" hreflang="fr" rel="alternate" title="Fran�ais"> fr </a></p>
</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>
<script type="text/javascript"><!--//--><![CDATA[//><!--
var comments_shortname = 'httpd';
var comments_identifier = 'http://httpd.apache.org/docs/trunk/rewrite/advanced.html';
(function(w, d) {
if (w.location.hostname.toLowerCase() == "httpd.apache.org") {
d.write('<div id="comments_thread"><\/div>');
var s = d.createElement('script');
s.type = 'text/javascript';
s.async = true;
s.src = 'https://comments.apache.org/show_comments.lua?site=' + comments_shortname + '&page=' + comments_identifier;
(d.getElementsByTagName('head')[0] || d.getElementsByTagName('body')[0]).appendChild(s);
}
else {
d.write('<div id="comments_thread">Comments are disabled for this page at the moment.<\/div>');
}
})(window, document);
//--><!]]></script></div><div id="footer">
<p class="apache">Copyright 2019 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>
<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></div><script type="text/javascript"><!--//--><![CDATA[//><!--
if (typeof(prettyPrint) !== 'undefined') {
prettyPrint();
}
//--><!]]></script>
</body></html>
|
