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10 <title>Advanced Techniques with mod_rewrite - Apache HTTP Server Version 2.5</title>
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20 <p class="apache">Apache HTTP Server Version 2.5</p>
21 <img alt="" src="../images/feather.png" /></div>
22 <div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
24 <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>
26 <p><span>Available Languages: </span><a href="../en/rewrite/advanced.html" title="English"> en </a> |
27 <a href="../fr/rewrite/advanced.html" hreflang="fr" rel="alternate" title="Français"> fr </a></p>
31 <p>This document supplements the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
32 <a href="../mod/mod_rewrite.html">reference documentation</a>. It provides
33 a few advanced techniques using mod_rewrite.</p>
37 <div class="warning">Note that many of these examples won't work unchanged in your
38 particular server configuration, so it's important that you understand
39 them, rather than merely cutting and pasting the examples into your
43 <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#sharding">URL-based sharding across multiple backends</a></li>
44 <li><img alt="" src="../images/down.gif" /> <a href="#on-the-fly-content">On-the-fly Content-Regeneration</a></li>
45 <li><img alt="" src="../images/down.gif" /> <a href="#load-balancing">Load Balancing</a></li>
46 <li><img alt="" src="../images/down.gif" /> <a href="#structuredhomedirs">Structured Userdirs</a></li>
47 <li><img alt="" src="../images/down.gif" /> <a href="#redirectanchors">Redirecting Anchors</a></li>
48 <li><img alt="" src="../images/down.gif" /> <a href="#time-dependent">Time-Dependent Rewriting</a></li>
49 <li><img alt="" src="../images/down.gif" /> <a href="#setenvvars">Set Environment Variables Based On URL Parts</a></li>
50 </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>
51 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
53 <h2><a name="sharding" id="sharding">URL-based sharding across multiple backends</a><a title="Permanent link" href="#sharding" class="permalink">¶</a></h2>
61 <p>A common technique for distributing the burden of
62 server load or storage space is called "sharding".
63 When using this method, a front-end server will use the
64 url to consistently "shard" users or objects to separate
71 <p>A mapping is maintained, from users to target servers, in
72 external map files. They look like:</p>
74 <div class="example"><p><code>
75 user1 physical_host_of_user1<br />
76 user2 physical_host_of_user2<br />
80 <p>We put this into a <code>map.users-to-hosts</code> file. The
83 <div class="example"><p><code>
89 <div class="example"><p><code>
90 http://physical_host_of_user1/u/user/anypath
93 <p>thus every URL path need not be valid on every backend physical
94 host. The following ruleset does this for us with the help of the map
95 files assuming that server0 is a default server which will be used if
96 a user has no entry in the map:</p>
98 <pre class="prettyprint lang-config">RewriteEngine on
99 RewriteMap users-to-hosts "txt:/path/to/map.users-to-hosts"
100 RewriteRule "^/u/([^/]+)/?(.*)" "http://${users-to-hosts:$1|server0}/u/$1/$2"</pre>
105 <p>See the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>
106 documentation for more discussion of the syntax of this directive.</p>
108 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
109 <div class="section">
110 <h2><a name="on-the-fly-content" id="on-the-fly-content">On-the-fly Content-Regeneration</a><a title="Permanent link" href="#on-the-fly-content" class="permalink">¶</a></h2>
115 <dt>Description:</dt>
118 <p>We wish to dynamically generate content, but store it
119 statically once it is generated. This rule will check for the
120 existence of the static file, and if it's not there, generate
121 it. The static files can be removed periodically, if desired (say,
122 via cron) and will be regenerated on demand.</p>
128 This is done via the following ruleset:
130 <pre class="prettyprint lang-config"># This example is valid in per-directory context only
131 RewriteCond "%{REQUEST_URI}" !-U
132 RewriteRule "^(.+)\.html$" "/regenerate_page.cgi" [PT,L]</pre>
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><a title="Permanent link" href="#load-balancing" class="permalink">¶</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">RewriteEngine on
171 RewriteMap lb "rnd:/path/to/serverlist.txt"
172 RewriteRule "^/(.*)" "http://${lb:servers}/$1" [P,L]</pre>
175 <p><code>serverlist.txt</code> will contain a list of the servers:</p>
177 <div class="example"><p><code>
178 ## serverlist.txt<br />
180 servers one.example.com|two.example.com|three.example.com<br />
183 <p>If you want one particular server to get more of the load than the
184 others, add it more times to the list.</p>
190 <p>Apache comes with a load-balancing module -
191 <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> - which is far more flexible and
192 featureful than anything you can cobble together using mod_rewrite.</p>
196 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
197 <div class="section">
198 <h2><a name="structuredhomedirs" id="structuredhomedirs">Structured Userdirs</a><a title="Permanent link" href="#structuredhomedirs" class="permalink">¶</a></h2>
203 <dt>Description:</dt>
206 <p>Some sites with thousands of users use a
207 structured homedir layout, <em>i.e.</em> each homedir is in a
208 subdirectory which begins (for instance) with the first
209 character of the username. So, <code>/~larry/anypath</code>
210 is <code>/home/<strong>l</strong>/larry/public_html/anypath</code>
211 while <code>/~waldo/anypath</code> is
212 <code>/home/<strong>w</strong>/waldo/public_html/anypath</code>.</p>
218 <p>We use the following ruleset to expand the tilde URLs
219 into the above layout.</p>
221 <pre class="prettyprint lang-config">RewriteEngine on
222 RewriteRule "^/~(<strong>([a-z])</strong>[a-z0-9]+)(.*)" "/home/<strong>$2</strong>/$1/public_html$3"</pre>
227 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
228 <div class="section">
229 <h2><a name="redirectanchors" id="redirectanchors">Redirecting Anchors</a><a title="Permanent link" href="#redirectanchors" class="permalink">¶</a></h2>
234 <dt>Description:</dt>
237 <p>By default, redirecting to an HTML anchor doesn't work,
238 because mod_rewrite escapes the <code>#</code> character,
239 turning it into <code>%23</code>. This, in turn, breaks the
246 <p>Use the <code>[NE]</code> flag on the
247 <code>RewriteRule</code>. NE stands for No Escape.
252 <dd>This technique will of course also work with other
253 special characters that mod_rewrite, by default, URL-encodes.</dd>
256 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
257 <div class="section">
258 <h2><a name="time-dependent" id="time-dependent">Time-Dependent Rewriting</a><a title="Permanent link" href="#time-dependent" class="permalink">¶</a></h2>
263 <dt>Description:</dt>
266 <p>We wish to use mod_rewrite to serve different content based on
273 <p>There are a lot of variables named <code>TIME_xxx</code>
274 for rewrite conditions. In conjunction with the special
275 lexicographic comparison patterns <code><STRING</code>,
276 <code>>STRING</code> and <code>=STRING</code> we can
277 do time-dependent redirects:</p>
279 <pre class="prettyprint lang-config">RewriteEngine on
280 RewriteCond "%{TIME_HOUR}%{TIME_MIN}" >0700
281 RewriteCond "%{TIME_HOUR}%{TIME_MIN}" <1900
282 RewriteRule "^foo\.html$" "foo.day.html" [L]
283 RewriteRule "^foo\.html$" "foo.night.html"</pre>
286 <p>This provides the content of <code>foo.day.html</code>
287 under the URL <code>foo.html</code> from
288 <code>07:01-18:59</code> and at the remaining time the
289 contents of <code>foo.night.html</code>.</p>
291 <div class="warning"><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>, intermediate proxies
292 and browsers may each cache responses and cause the either page to be
293 shown outside of the time-window configured.
294 <code class="module"><a href="../mod/mod_expires.html">mod_expires</a></code> may be used to control this
295 effect. You are, of course, much better off simply serving the
296 content dynamically, and customizing it based on the time of day.</div>
301 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
302 <div class="section">
303 <h2><a name="setenvvars" id="setenvvars">Set Environment Variables Based On URL Parts</a><a title="Permanent link" href="#setenvvars" class="permalink">¶</a></h2>
308 <dt>Description:</dt>
311 <p>At time, we want to maintain some kind of status when we
312 perform a rewrite. For example, you want to make a note that
313 you've done that rewrite, so that you can check later to see if a
314 request can via that rewrite. One way to do this is by setting an
315 environment variable.</p>
321 <p>Use the [E] flag to set an environment variable.</p>
323 <pre class="prettyprint lang-config">RewriteEngine on
324 RewriteRule "^/horse/(.*)" "/pony/$1" [E=<strong>rewritten:1</strong>]</pre>
327 <p>Later in your ruleset you might check for this environment
328 variable using a RewriteCond:</p>
330 <pre class="prettyprint lang-config">RewriteCond "%{ENV:rewritten}" =1</pre>
333 <p>Note that environment variables do not survive an external
334 redirect. You might consider using the [CO] flag to set a
341 <div class="bottomlang">
342 <p><span>Available Languages: </span><a href="../en/rewrite/advanced.html" title="English"> en </a> |
343 <a href="../fr/rewrite/advanced.html" hreflang="fr" rel="alternate" title="Français"> fr </a></p>
344 </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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