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 2.4</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 2.4</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> | 25<a href="../fr/rewrite/avoid.html" hreflang="fr" rel="alternate" title="Fran�ais"> fr </a></p> 26</div> 27 28 29<p>This document supplements the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> 30<a href="../mod/mod_rewrite.html">reference documentation</a>. It provides 31a few advanced techniques using mod_rewrite.</p> 32 33<div class="warning">Note that many of these examples won't work unchanged in your 34particular server configuration, so it's important that you understand 35them, rather than merely cutting and pasting the examples into your 36configuration.</div> 37 38</div> 39<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#sharding">URL-based sharding accross multiple backends</a></li> 40<li><img alt="" src="../images/down.gif" /> <a href="#on-the-fly-content">On-the-fly Content-Regeneration</a></li> 41<li><img alt="" src="../images/down.gif" /> <a href="#load-balancing">Load Balancing</a></li> 42<li><img alt="" src="../images/down.gif" /> <a href="#autorefresh">Document With Autorefresh</a></li> 43<li><img alt="" src="../images/down.gif" /> <a href="#structuredhomedirs">Structured Userdirs</a></li> 44<li><img alt="" src="../images/down.gif" /> <a href="#redirectanchors">Redirecting Anchors</a></li> 45<li><img alt="" src="../images/down.gif" /> <a href="#time-dependent">Time-Dependent Rewriting</a></li> 46<li><img alt="" src="../images/down.gif" /> <a href="#setenvvars">Set Environment Variables Based On URL Parts</a></li> 47</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> 48<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 49<div class="section"> 50<h2><a name="sharding" id="sharding">URL-based sharding accross multiple backends</a></h2> 51 52 53 54 <dl> 55 <dt>Description:</dt> 56 57 <dd> 58 <p>A common technique for distributing the burden of 59 server load or storage space is called "sharding". 60 When using this method, a front-end server will use the 61 url to consistently "shard" users or objects to separate 62 backend servers.</p> 63 </dd> 64 65 <dt>Solution:</dt> 66 67 <dd> 68 <p>A mapping is maintained, from users to target servers, in 69 external map files. They look like:</p> 70 71<div class="example"><p><code> 72user1 physical_host_of_user1<br /> 73user2 physical_host_of_user2<br /> 74: : 75</code></p></div> 76 77 <p>We put this into a <code>map.users-to-hosts</code> file. The 78 aim is to map;</p> 79 80<div class="example"><p><code> 81/u/user1/anypath 82</code></p></div> 83 84 <p>to</p> 85 86<div class="example"><p><code> 87http://physical_host_of_user1/u/user/anypath 88</code></p></div> 89 90 <p>thus every URL path need not be valid on every backend physical 91 host. The following ruleset does this for us with the help of the map 92 files assuming that server0 is a default server which will be used if 93 a user has no entry in the map:</p> 94 95<pre class="prettyprint lang-config"> 96RewriteEngine on 97RewriteMap users-to-hosts txt:/path/to/map.users-to-hosts 98RewriteRule ^/u/([^/]+)/?(.*) http://${users-to-hosts:$1|server0}/u/$1/$2 99</pre> 100 101 </dd> 102 </dl> 103 104 <p>See the <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> 105 documentation for more discussion of the syntax of this directive.</p> 106 107</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 108<div class="section"> 109<h2><a name="on-the-fly-content" id="on-the-fly-content">On-the-fly Content-Regeneration</a></h2> 110 111 112 113 <dl> 114 <dt>Description:</dt> 115 116 <dd> 117 <p>We wish to dynamically generate content, but store it 118 statically once it is generated. This rule will check for the 119 existence of the static file, and if it's not there, generate 120 it. The static files can be removed periodically, if desired (say, 121 via cron) and will be regenerated on demand.</p> 122 </dd> 123 124 <dt>Solution:</dt> 125 126 <dd> 127 This is done via the following ruleset: 128 129<pre class="prettyprint lang-config"> 130# This example is valid in per-directory context only 131RewriteCond %{REQUEST_URI} !-U 132RewriteRule ^(.+)\.html$ /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<pre class="prettyprint lang-config"> 172RewriteEngine on 173RewriteMap lb rnd:/path/to/serverlist.txt 174RewriteRule ^/(.*) http://${lb:servers}/$1 [P,L] 175</pre> 176 177 178<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> 202 203 204 205 206 207 <dl> 208 <dt>Description:</dt> 209 210 <dd> 211 <p>Wouldn't it be nice, while creating a complex web page, if 212 the web browser would automatically refresh the page every 213 time we save a new version from within our editor? 214 Impossible?</p> 215 </dd> 216 217 <dt>Solution:</dt> 218 219 <dd> 220 <p>No! We just combine the MIME multipart feature, the 221 web server NPH feature, and the URL manipulation power of 222 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>. First, we establish a new 223 URL feature: Adding just <code>:refresh</code> to any 224 URL causes the 'page' to be refreshed every time it is 225 updated on the filesystem.</p> 226 227<pre class="prettyprint lang-config"> 228RewriteRule ^(/[uge]/[^/]+/?.*):refresh /internal/cgi/apache/nph-refresh?f=$1 229</pre> 230 231 232 <p>Now when we reference the URL</p> 233 234<div class="example"><p><code> 235/u/foo/bar/page.html:refresh 236</code></p></div> 237 238 <p>this leads to the internal invocation of the URL</p> 239 240<div class="example"><p><code> 241/internal/cgi/apache/nph-refresh?f=/u/foo/bar/page.html 242</code></p></div> 243 244 <p>The only missing part is the NPH-CGI script. Although 245 one would usually say "left as an exercise to the reader" 246 ;-) I will provide this, too.</p> 247 248<pre class="prettyprint lang-perl"> 249#!/sw/bin/perl 250## 251## nph-refresh -- NPH/CGI script for auto refreshing pages 252## Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved. 253## 254$| = 1; 255 256# split the QUERY_STRING variable 257@pairs = split( /&/, $ENV{'QUERY_STRING'} ); 258foreach $pair (@pairs) { 259 ( $name, $value ) = split( /=/, $pair ); 260 $name =~ tr/A-Z/a-z/; 261 $name = 'QS_' . $name; 262 $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg; 263 eval "\$$name = \"$value\""; 264} 265$QS_s = 1 if ( $QS_s eq '' ); 266$QS_n = 3600 if ( $QS_n eq '' ); 267if ( $QS_f eq '' ) { 268 print "HTTP/1.0 200 OK\n"; 269 print "Content-type: text/html\n\n"; 270 print "<b>ERROR</b>: No file given\n"; 271 exit(0); 272} 273if ( !-f $QS_f ) { 274 print "HTTP/1.0 200 OK\n"; 275 print "Content-type: text/html\n\n"; 276 print "<b>ERROR</b>: File $QS_f not found\n"; 277 exit(0); 278} 279 280sub print_http_headers_multipart_begin { 281 print "HTTP/1.0 200 OK\n"; 282 $bound = "ThisRandomString12345"; 283 print "Content-type: multipart/x-mixed-replace;boundary=$bound\n"; 284 &print_http_headers_multipart_next; 285} 286 287sub print_http_headers_multipart_next { 288 print "\n--$bound\n"; 289} 290 291sub print_http_headers_multipart_end { 292 print "\n--$bound--\n"; 293} 294 295sub displayhtml { 296 local ($buffer) = @_; 297 $len = length($buffer); 298 print "Content-type: text/html\n"; 299 print "Content-length: $len\n\n"; 300 print $buffer; 301} 302 303sub readfile { 304 local ($file) = @_; 305 local ( *FP, $size, $buffer, $bytes ); 306 ( $x, $x, $x, $x, $x, $x, $x, $size ) = stat($file); 307 $size = sprintf( "%d", $size ); 308 open( FP, "<$file" ); 309 $bytes = sysread( FP, $buffer, $size ); 310 close(FP); 311 return $buffer; 312} 313 314$buffer = &readfile($QS_f); 315&print_http_headers_multipart_begin; 316&displayhtml($buffer); 317 318sub mystat { 319 local ($file) = $_[0]; 320 local ($time); 321 322 ( $x, $x, $x, $x, $x, $x, $x, $x, $x, $mtime ) = stat($file); 323 return $mtime; 324} 325 326$mtimeL = &mystat($QS_f); 327$mtime = $mtime; 328for ( $n = 0 ; $n & lt ; $QS_n ; $n++ ) { 329 while (1) { 330 $mtime = &mystat($QS_f); 331 if ( $mtime ne $mtimeL ) { 332 $mtimeL = $mtime; 333 sleep(2); 334 $buffer = &readfile($QS_f); 335 &print_http_headers_multipart_next; 336 &displayhtml($buffer); 337 sleep(5); 338 $mtimeL = &mystat($QS_f); 339 last; 340 } 341 sleep($QS_s); 342 } 343} 344 345&print_http_headers_multipart_end; 346 347exit(0); 348 349##EOF## 350</pre> 351 352 </dd> 353 </dl> 354 355</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 356<div class="section"> 357<h2><a name="structuredhomedirs" id="structuredhomedirs">Structured Userdirs</a></h2> 358 359 360 361 <dl> 362 <dt>Description:</dt> 363 364 <dd> 365 <p>Some sites with thousands of users use a 366 structured homedir layout, <em>i.e.</em> each homedir is in a 367 subdirectory which begins (for instance) with the first 368 character of the username. So, <code>/~larry/anypath</code> 369 is <code>/home/<strong>l</strong>/larry/public_html/anypath</code> 370 while <code>/~waldo/anypath</code> is 371 <code>/home/<strong>w</strong>/waldo/public_html/anypath</code>.</p> 372 </dd> 373 374 <dt>Solution:</dt> 375 376 <dd> 377 <p>We use the following ruleset to expand the tilde URLs 378 into the above layout.</p> 379 380<pre class="prettyprint lang-config"> 381RewriteEngine on 382RewriteRule ^/~(<strong>([a-z])</strong>[a-z0-9]+)(.*) /home/<strong>$2</strong>/$1/public_html$3 383</pre> 384 385 </dd> 386 </dl> 387 388</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 389<div class="section"> 390<h2><a name="redirectanchors" id="redirectanchors">Redirecting Anchors</a></h2> 391 392 393 394 <dl> 395 <dt>Description:</dt> 396 397 <dd> 398 <p>By default, redirecting to an HTML anchor doesn't work, 399 because mod_rewrite escapes the <code>#</code> character, 400 turning it into <code>%23</code>. This, in turn, breaks the 401 redirection.</p> 402 </dd> 403 404 <dt>Solution:</dt> 405 406 <dd> 407 <p>Use the <code>[NE]</code> flag on the 408 <code>RewriteRule</code>. NE stands for No Escape. 409 </p> 410 </dd> 411 412 <dt>Discussion:</dt> 413 <dd>This technique will of course also work with other 414 special characters that mod_rewrite, by default, URL-encodes.</dd> 415 </dl> 416 417</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 418<div class="section"> 419<h2><a name="time-dependent" id="time-dependent">Time-Dependent Rewriting</a></h2> 420 421 422 423 <dl> 424 <dt>Description:</dt> 425 426 <dd> 427 <p>We wish to use mod_rewrite to serve different content based on 428 the time of day.</p> 429 </dd> 430 431 <dt>Solution:</dt> 432 433 <dd> 434 <p>There are a lot of variables named <code>TIME_xxx</code> 435 for rewrite conditions. In conjunction with the special 436 lexicographic comparison patterns <code><STRING</code>, 437 <code>>STRING</code> and <code>=STRING</code> we can 438 do time-dependent redirects:</p> 439 440<pre class="prettyprint lang-config"> 441RewriteEngine on 442RewriteCond %{TIME_HOUR}%{TIME_MIN} >0700 443RewriteCond %{TIME_HOUR}%{TIME_MIN} <1900 444RewriteRule ^foo\.html$ foo.day.html [L] 445RewriteRule ^foo\.html$ foo.night.html 446</pre> 447 448 449 <p>This provides the content of <code>foo.day.html</code> 450 under the URL <code>foo.html</code> from 451 <code>07:01-18:59</code> and at the remaining time the 452 contents of <code>foo.night.html</code>.</p> 453 454 <div class="warning"><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>, intermediate proxies 455 and browsers may each cache responses and cause the either page to be 456 shown outside of the time-window configured. 457 <code class="module"><a href="../mod/mod_expires.html">mod_expires</a></code> may be used to control this 458 effect. You are, of course, much better off simply serving the 459 content dynamically, and customizing it based on the time of day.</div> 460 461 </dd> 462 </dl> 463 464</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 465<div class="section"> 466<h2><a name="setenvvars" id="setenvvars">Set Environment Variables Based On URL Parts</a></h2> 467 468 469 470 <dl> 471 <dt>Description:</dt> 472 473 <dd> 474 <p>At time, we want to maintain some kind of status when we 475 perform a rewrite. For example, you want to make a note that 476 you've done that rewrite, so that you can check later to see if a 477 request can via that rewrite. One way to do this is by setting an 478 environment variable.</p> 479 </dd> 480 481 <dt>Solution:</dt> 482 483 <dd> 484 <p>Use the [E] flag to set an environment variable.</p> 485 486<pre class="prettyprint lang-config"> 487RewriteEngine on 488RewriteRule ^/horse/(.*) /pony/$1 [E=<strong>rewritten:1</strong>] 489</pre> 490 491 492 <p>Later in your ruleset you might check for this environment 493 variable using a RewriteCond:</p> 494 495<pre class="prettyprint lang-config"> 496RewriteCond %{ENV:rewritten} =1 497</pre> 498 499 500 <p>Note that environment variables do not survive an external 501 redirect. You might consider using the [CO] flag to set a 502 cookie.</p> 503 504 </dd> 505 </dl> 506 507</div></div> 508<div class="bottomlang"> 509<p><span>Available Languages: </span><a href="../en/rewrite/avoid.html" title="English"> en </a> | 510<a href="../fr/rewrite/avoid.html" hreflang="fr" rel="alternate" title="Fran�ais"> fr </a></p> 511</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. 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