1<?xml version="1.0" encoding="ISO-8859-1"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!-- 4 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 5 This file is generated from xml source: DO NOT EDIT 6 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 7 --> 8<title>Advanced Techniques with mod_rewrite - Apache HTTP Server</title> 9<link href="/style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> 10<link href="/style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> 11<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" /> 12<script src="/style/scripts/prettify.js" type="text/javascript"> 13</script> 14 15<link href="/images/favicon.ico" rel="shortcut icon" /></head> 16<body id="manual-page"><div id="page-header"> 17<p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/directives.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 2.2</p> 19<img alt="" src="/images/feather.gif" /></div> 20<div class="up"><a href="./"><img title="<-" alt="<-" src="/images/left.gif" /></a></div> 21<div id="path"> 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 2.2</a> > <a href="./">Rewrite</a></div><div id="page-content"><div id="preamble"><h1>Advanced Techniques with mod_rewrite</h1> 23<div class="toplang"> 24<p><span>Available Languages: </span><a href="/en/rewrite/avoid.html" title="English"> en </a></p> 25</div> 26 27 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 30a few advanced techniques and tricks using mod_rewrite.</p> 31 32<div class="warning">Note that many of these examples won't work unchanged in your 33particular server configuration, so it's important that you understand 34them, rather than merely cutting and pasting the examples into your 35configuration.</div> 36 37</div> 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> 48<div class="section"> 49<h2><a name="sharding" id="sharding">URL-based sharding accross multiple backends</a></h2> 50 51 52 53 <dl> 54 <dt>Description:</dt> 55 56 <dd> 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 61 backend servers.</p> 62 </dd> 63 64 <dt>Solution:</dt> 65 66 <dd> 67 <p>A mapping is maintained, from users to target servers, in 68 external map files. They look like:</p> 69 70<div class="example"><p><code> 71user1 physical_host_of_user1<br /> 72user2 physical_host_of_user2<br /> 73: : 74</code></p></div> 75 76 <p>We put this into a <code>map.users-to-hosts</code> file. The 77 aim is to map;</p> 78 79<div class="example"><p><code> 80/u/user1/anypath 81</code></p></div> 82 83 <p>to</p> 84 85<div class="example"><p><code> 86http://physical_host_of_user1/u/user/anypath 87</code></p></div> 88 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> 93 94<div class="example"><p><code> 95RewriteEngine on<br /> 96<br /> 97RewriteMap users-to-hosts txt:/path/to/map.users-to-hosts<br /> 98<br /> 99RewriteRule ^/u/<strong>([^/]+)</strong>/?(.*) http://<strong>${users-to-hosts:$1|server0}</strong>/u/$1/$2 100</code></p></div> 101 </dd> 102 </dl> 103 104 <p>See the <code class="directive"><a href="/mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> 105 documentation for more discussion of the syntax of this directive.</p> 106 107</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 108<div class="section"> 109<h2><a name="on-the-fly-content" id="on-the-fly-content">On-the-fly Content-Regeneration</a></h2> 110 111 112 113 <dl> 114 <dt>Description:</dt> 115 116 <dd> 117 <p>We wish to dynamically generate content, but store it 118 statically once it is generated. This rule will check for the 119 existence of the static file, and if it's not there, generate 120 it. The static files can be removed periodically, if desired (say, 121 via cron) and will be regenerated on demand.</p> 122 </dd> 123 124 <dt>Solution:</dt> 125 126 <dd> 127 This is done via the following ruleset: 128 129<pre class="prettyprint lang-config"> 130# This example is valid in per-directory context only 131RewriteCond %{REQUEST_URI} !-U 132RewriteRule ^(.+)\.html$ /regenerate_page.cgi [PT,L] 133</pre> 134 135 136 <p>The <code>-U</code> operator determines whether the test string 137 (in this case, <code>REQUEST_URI</code>) is a valid URL. It does 138 this via a subrequest. In the event that this subrequest fails - 139 that is, the requested resource doesn't exist - this rule invokes 140 the CGI program <code>/regenerate_page.cgi</code>, which generates 141 the requested resource and saves it into the document directory, so 142 that the next time it is requested, a static copy can be served.</p> 143 144 <p>In this way, documents that are infrequently updated can be served in 145 static form. if documents need to be refreshed, they can be deleted 146 from the document directory, and they will then be regenerated the 147 next time they are requested.</p> 148 </dd> 149 </dl> 150 151</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 152<div class="section"> 153<h2><a name="load-balancing" id="load-balancing">Load Balancing</a></h2> 154 155 156 157 <dl> 158 <dt>Description:</dt> 159 160 <dd> 161 <p>We wish to randomly distribute load across several servers 162 using mod_rewrite.</p> 163 </dd> 164 165 <dt>Solution:</dt> 166 167 <dd> 168 <p>We'll use <code class="directive"><a href="/mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> and a list of servers 169 to accomplish this.</p> 170 171<div class="example"><p><code> 172RewriteEngine on<br /> 173RewriteMap lb rnd:/path/to/serverlist.txt<br /> 174<br /> 175RewriteRule ^/(.*) http://${lb:servers}/$1 [P,L] 176</code></p></div> 177 178<p><code>serverlist.txt</code> will contain a list of the servers:</p> 179 180<div class="example"><p><code> 181## serverlist.txt<br /> 182<br /> 183servers one.example.com|two.example.com|three.example.com<br /> 184</code></p></div> 185 186<p>If you want one particular server to get more of the load than the 187others, add it more times to the list.</p> 188 189 </dd> 190 191 <dt>Discussion</dt> 192 <dd> 193<p>Apache comes with a load-balancing module - 194<code class="module"><a href="/mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> - which is far more flexible and 195featureful than anything you can cobble together using mod_rewrite.</p> 196 </dd> 197 </dl> 198 199</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 200<div class="section"> 201<h2><a name="autorefresh" id="autorefresh">Document With Autorefresh</a></h2> 202 203 204 205 <dl> 206 <dt>Description:</dt> 207 208 <dd> 209 <p>Wouldn't it be nice, while creating a complex web page, if 210 the web browser would automatically refresh the page every 211 time we save a new version from within our editor? 212 Impossible?</p> 213 </dd> 214 215 <dt>Solution:</dt> 216 217 <dd> 218 <p>No! We just combine the MIME multipart feature, the 219 web server NPH feature, and the URL manipulation power of 220 <code class="module"><a href="/mod/mod_rewrite.html">mod_rewrite</a></code>. First, we establish a new 221 URL feature: Adding just <code>:refresh</code> to any 222 URL causes the 'page' to be refreshed every time it is 223 updated on the filesystem.</p> 224 225<div class="example"><p><code> 226RewriteRule ^(/[uge]/[^/]+/?.*):refresh /internal/cgi/apache/nph-refresh?f=$1 227</code></p></div> 228 229 <p>Now when we reference the URL</p> 230 231<div class="example"><p><code> 232/u/foo/bar/page.html:refresh 233</code></p></div> 234 235 <p>this leads to the internal invocation of the URL</p> 236 237<div class="example"><p><code> 238/internal/cgi/apache/nph-refresh?f=/u/foo/bar/page.html 239</code></p></div> 240 241 <p>The only missing part is the NPH-CGI script. Although 242 one would usually say "left as an exercise to the reader" 243 ;-) I will provide this, too.</p> 244 245<div class="example"><pre> 246#!/sw/bin/perl 247## 248## nph-refresh -- NPH/CGI script for auto refreshing pages 249## Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved. 250## 251$| = 1; 252 253# split the QUERY_STRING variable 254@pairs = split( /&/, $ENV{'QUERY_STRING'} ); 255foreach $pair (@pairs) { 256 ( $name, $value ) = split( /=/, $pair ); 257 $name =~ tr/A-Z/a-z/; 258 $name = 'QS_' . $name; 259 $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg; 260 eval "\$$name = \"$value\""; 261} 262$QS_s = 1 if ( $QS_s eq '' ); 263$QS_n = 3600 if ( $QS_n eq '' ); 264if ( $QS_f eq '' ) { 265 print "HTTP/1.0 200 OK\n"; 266 print "Content-type: text/html\n\n"; 267print "&lt;b&gt;ERROR&lt;/b&gt;: No file given\n"; 268 exit(0); 269} 270if ( !-f $QS_f ) { 271 print "HTTP/1.0 200 OK\n"; 272 print "Content-type: text/html\n\n"; 273print "&lt;b&gt;ERROR&lt;/b&gt;: File $QS_f not found\n"; 274 exit(0); 275} 276 277sub print_http_headers_multipart_begin { 278 print "HTTP/1.0 200 OK\n"; 279 $bound = "ThisRandomString12345"; 280 print "Content-type: multipart/x-mixed-replace;boundary=$bound\n"; 281 &print_http_headers_multipart_next; 282} 283 284sub print_http_headers_multipart_next { 285 print "\n--$bound\n"; 286} 287 288sub print_http_headers_multipart_end { 289 print "\n--$bound--\n"; 290} 291 292sub displayhtml { 293 local ($buffer) = @_; 294 $len = length($buffer); 295 print "Content-type: text/html\n"; 296 print "Content-length: $len\n\n"; 297 print $buffer; 298} 299 300sub readfile { 301 local ($file) = @_; 302 local ( *FP, $size, $buffer, $bytes ); 303 ( $x, $x, $x, $x, $x, $x, $x, $size ) = stat($file); 304 $size = sprintf( "%d", $size ); 305open(FP, "&lt;$file"); 306 $bytes = sysread( FP, $buffer, $size ); 307 close(FP); 308 return $buffer; 309} 310 311$buffer = &readfile($QS_f); 312&print_http_headers_multipart_begin; 313&displayhtml($buffer); 314 315sub mystat { 316 local ($file) = $_[0]; 317 local ($time); 318 319 ( $x, $x, $x, $x, $x, $x, $x, $x, $x, $mtime ) = stat($file); 320 return $mtime; 321} 322 323$mtimeL = &mystat($QS_f); 324$mtime = $mtime; 325for ( $n = 0 ; $n & lt ; $QS_n ; $n++ ) { 326 while (1) { 327 $mtime = &mystat($QS_f); 328 if ( $mtime ne $mtimeL ) { 329 $mtimeL = $mtime; 330 sleep(2); 331 $buffer = &readfile($QS_f); 332 &print_http_headers_multipart_next; 333 &displayhtml($buffer); 334 sleep(5); 335 $mtimeL = &mystat($QS_f); 336 last; 337 } 338 sleep($QS_s); 339 } 340} 341 342&print_http_headers_multipart_end; 343 344exit(0); 345 346##EOF## 347</pre></div> 348 </dd> 349 </dl> 350 351</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 352<div class="section"> 353<h2><a name="structuredhomedirs" id="structuredhomedirs">Structured Userdirs</a></h2> 354 355 356 357 <dl> 358 <dt>Description:</dt> 359 360 <dd> 361 <p>Some sites with thousands of users use a 362 structured homedir layout, <em>i.e.</em> each homedir is in a 363 subdirectory which begins (for instance) with the first 364 character of the username. So, <code>/~larry/anypath</code> 365 is <code>/home/<strong>l</strong>/larry/public_html/anypath</code> 366 while <code>/~waldo/anypath</code> is 367 <code>/home/<strong>w</strong>/waldo/public_html/anypath</code>.</p> 368 </dd> 369 370 <dt>Solution:</dt> 371 372 <dd> 373 <p>We use the following ruleset to expand the tilde URLs 374 into the above layout.</p> 375 376<div class="example"><p><code> 377RewriteEngine on<br /> 378RewriteRule ^/~(<strong>([a-z])</strong>[a-z0-9]+)(.*) /home/<strong>$2</strong>/$1/public_html$3 379</code></p></div> 380 </dd> 381 </dl> 382 383</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 384<div class="section"> 385<h2><a name="redirectanchors" id="redirectanchors">Redirecting Anchors</a></h2> 386 387 388 389 <dl> 390 <dt>Description:</dt> 391 392 <dd> 393 <p>By default, redirecting to an HTML anchor doesn't work, 394 because mod_rewrite escapes the <code>#</code> character, 395 turning it into <code>%23</code>. This, in turn, breaks the 396 redirection.</p> 397 </dd> 398 399 <dt>Solution:</dt> 400 401 <dd> 402 <p>Use the <code>[NE]</code> flag on the 403 <code>RewriteRule</code>. NE stands for No Escape. 404 </p> 405 </dd> 406 407 <dt>Discussion:</dt> 408 <dd>This technique will of course also work with other 409 special characters that mod_rewrite, by default, URL-encodes.</dd> 410 </dl> 411 412</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 413<div class="section"> 414<h2><a name="time-dependent" id="time-dependent">Time-Dependent Rewriting</a></h2> 415 416 417 418 <dl> 419 <dt>Description:</dt> 420 421 <dd> 422 <p>We wish to use mod_rewrite to serve different content based on 423 the time of day.</p> 424 </dd> 425 426 <dt>Solution:</dt> 427 428 <dd> 429 <p>There are a lot of variables named <code>TIME_xxx</code> 430 for rewrite conditions. In conjunction with the special 431 lexicographic comparison patterns <code><STRING</code>, 432 <code>>STRING</code> and <code>=STRING</code> we can 433 do time-dependent redirects:</p> 434 435<div class="example"><p><code> 436RewriteEngine on<br /> 437RewriteCond %{TIME_HOUR}%{TIME_MIN} >0700<br /> 438RewriteCond %{TIME_HOUR}%{TIME_MIN} <1900<br /> 439RewriteRule ^foo\.html$ foo.day.html [L]<br /> 440RewriteRule ^foo\.html$ foo.night.html 441</code></p></div> 442 443 <p>This provides the content of <code>foo.day.html</code> 444 under the URL <code>foo.html</code> from 445 <code>07:01-18:59</code> and at the remaining time the 446 contents of <code>foo.night.html</code>.</p> 447 448 <div class="warning"><code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code>, intermediate proxies 449 and browsers may each cache responses and cause the either page to be 450 shown outside of the time-window configured. 451 <code class="module"><a href="/mod/mod_expires.html">mod_expires</a></code> may be used to control this 452 effect. You are, of course, much better off simply serving the 453 content dynamically, and customizing it based on the time of day.</div> 454 455 </dd> 456 </dl> 457 458</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 459<div class="section"> 460<h2><a name="setenvvars" id="setenvvars">Set Environment Variables Based On URL Parts</a></h2> 461 462 463 464 <dl> 465 <dt>Description:</dt> 466 467 <dd> 468 <p>At time, we want to maintain some kind of status when we 469 perform a rewrite. For example, you want to make a note that 470 you've done that rewrite, so that you can check later to see if a 471 request can via that rewrite. One way to do this is by setting an 472 environment variable.</p> 473 </dd> 474 475 <dt>Solution:</dt> 476 477 <dd> 478 <p>Use the [E] flag to set an environment variable.</p> 479 480<div class="example"><p><code> 481RewriteEngine on<br /> 482RewriteRule ^/horse/(.*) /pony/$1 [E=<strong>rewritten:1</strong>] 483</code></p></div> 484 485 <p>Later in your ruleset you might check for this environment 486 variable using a RewriteCond:</p> 487 488<div class="example"><p><code> 489RewriteCond %{ENV:rewritten} =1 490</code></p></div> 491 492 </dd> 493 </dl> 494 495</div></div> 496<div class="bottomlang"> 497<p><span>Available Languages: </span><a href="/en/rewrite/avoid.html" title="English"> en </a></p> 498</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. 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