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Posted to cvs@httpd.apache.org by rb...@apache.org on 2009/11/02 21:36:32 UTC
svn commit: r832094 [3/4] - /httpd/httpd/trunk/docs/manual/rewrite/
Modified: httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide_advanced.html.en
URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide_advanced.html.en?rev=832094&r1=832093&r2=832094&view=diff
==============================================================================
--- httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide_advanced.html.en (original)
+++ httpd/httpd/trunk/docs/manual/rewrite/rewrite_guide_advanced.html.en Mon Nov 2 20:36:30 2009
@@ -41,1251 +41,11 @@
avoids many problems.</div>
</div>
-<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#cluster">Web Cluster with Consistent URL Space</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#structuredhomedirs">Structured Homedirs</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#filereorg">Filesystem Reorganization</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#redirect404">Redirect Failing URLs to Another Web Server</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#archive-access-multiplexer">Archive Access Multiplexer</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#browser-dependent-content">Browser Dependent Content</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#dynamic-mirror">Dynamic Mirror</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#reverse-dynamic-mirror">Reverse Dynamic Mirror</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#retrieve-missing-data">Retrieve Missing Data from Intranet</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="#new-mime-type">New MIME-type, New Service</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="#autorefresh">Document With Autorefresh</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#mass-virtual-hosting">Mass Virtual Hosting</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#host-deny">Host Deny</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#proxy-deny">Proxy Deny</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#special-authentication">Special Authentication Variant</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#referer-deflector">Referer-based Deflector</a></li>
-</ul><h3>See also</h3><ul class="seealso"><li><a href="../mod/mod_rewrite.html">Module
+<div id="quickview"><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="rewrite_guide.html">Rewrite Guide - useful
examples</a></li><li><a href="tech.html">Technical details</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="cluster" id="cluster">Web Cluster with Consistent URL Space</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>We want to create a homogeneous and consistent URL
- layout across all WWW servers on an Intranet web cluster, i.e.,
- all URLs (by definition server-local and thus
- server-dependent!) become server <em>independent</em>!
- What we want is to give the WWW namespace a single consistent
- layout: no URL should refer to
- any particular target server. The cluster itself
- should connect users automatically to a physical target
- host as needed, invisibly.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>First, the knowledge of the target servers comes from
- (distributed) external maps which contain information on
- where our users, groups, and entities reside. They have the
- form:</p>
-
-<div class="example"><pre>
-user1 server_of_user1
-user2 server_of_user2
-: :
-</pre></div>
-
- <p>We put them into files <code>map.xxx-to-host</code>.
- Second we need to instruct all servers to redirect URLs
- of the forms:</p>
-
-<div class="example"><pre>
-/u/user/anypath
-/g/group/anypath
-/e/entity/anypath
-</pre></div>
-
- <p>to</p>
-
-<div class="example"><pre>
-http://physical-host/u/user/anypath
-http://physical-host/g/group/anypath
-http://physical-host/e/entity/anypath
-</pre></div>
-
- <p>when any URL path need not be valid on every server. 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>
-
-<div class="example"><pre>
-RewriteEngine on
-
-RewriteMap user-to-host txt:/path/to/map.user-to-host
-RewriteMap group-to-host txt:/path/to/map.group-to-host
-RewriteMap entity-to-host txt:/path/to/map.entity-to-host
-
-RewriteRule ^/u/<strong>([^/]+)</strong>/?(.*) http://<strong>${user-to-host:$1|server0}</strong>/u/$1/$2
-RewriteRule ^/g/<strong>([^/]+)</strong>/?(.*) http://<strong>${group-to-host:$1|server0}</strong>/g/$1/$2
-RewriteRule ^/e/<strong>([^/]+)</strong>/?(.*) http://<strong>${entity-to-host:$1|server0}</strong>/e/$1/$2
-
-RewriteRule ^/([uge])/([^/]+)/?$ /$1/$2/.www/
-RewriteRule ^/([uge])/([^/]+)/([^.]+.+) /$1/$2/.www/$3\
-</pre></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="structuredhomedirs" id="structuredhomedirs">Structured Homedirs</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>/~foo/anypath</code>
- is <code>/home/<strong>f</strong>/foo/.www/anypath</code>
- while <code>/~bar/anypath</code> is
- <code>/home/<strong>b</strong>/bar/.www/anypath</code>.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We use the following ruleset to expand the tilde URLs
- into the above layout.</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteRule ^/~(<strong>([a-z])</strong>[a-z0-9]+)(.*) /home/<strong>$2</strong>/$1/.www$3
-</pre></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="filereorg" id="filereorg">Filesystem Reorganization</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>This really is a hardcore example: a killer application
- which heavily uses per-directory
- <code>RewriteRules</code> to get a smooth look and feel
- on the Web while its data structure is never touched or
- adjusted. Background: <strong><em>net.sw</em></strong> is
- my archive of freely available Unix software packages,
- which I started to collect in 1992. It is both my hobby
- and job to do this, because while I'm studying computer
- science I have also worked for many years as a system and
- network administrator in my spare time. Every week I need
- some sort of software so I created a deep hierarchy of
- directories where I stored the packages:</p>
-
-<div class="example"><pre>
-drwxrwxr-x 2 netsw users 512 Aug 3 18:39 Audio/
-drwxrwxr-x 2 netsw users 512 Jul 9 14:37 Benchmark/
-drwxrwxr-x 12 netsw users 512 Jul 9 00:34 Crypto/
-drwxrwxr-x 5 netsw users 512 Jul 9 00:41 Database/
-drwxrwxr-x 4 netsw users 512 Jul 30 19:25 Dicts/
-drwxrwxr-x 10 netsw users 512 Jul 9 01:54 Graphic/
-drwxrwxr-x 5 netsw users 512 Jul 9 01:58 Hackers/
-drwxrwxr-x 8 netsw users 512 Jul 9 03:19 InfoSys/
-drwxrwxr-x 3 netsw users 512 Jul 9 03:21 Math/
-drwxrwxr-x 3 netsw users 512 Jul 9 03:24 Misc/
-drwxrwxr-x 9 netsw users 512 Aug 1 16:33 Network/
-drwxrwxr-x 2 netsw users 512 Jul 9 05:53 Office/
-drwxrwxr-x 7 netsw users 512 Jul 9 09:24 SoftEng/
-drwxrwxr-x 7 netsw users 512 Jul 9 12:17 System/
-drwxrwxr-x 12 netsw users 512 Aug 3 20:15 Typesetting/
-drwxrwxr-x 10 netsw users 512 Jul 9 14:08 X11/
-</pre></div>
-
- <p>In July 1996 I decided to make this archive public to
- the world via a nice Web interface. "Nice" means that I
- wanted to offer an interface where you can browse
- directly through the archive hierarchy. And "nice" means
- that I didn't want to change anything inside this
- hierarchy - not even by putting some CGI scripts at the
- top of it. Why? Because the above structure should later be
- accessible via FTP as well, and I didn't want any
- Web or CGI stuff mixed in there.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>The solution has two parts: The first is a set of CGI
- scripts which create all the pages at all directory
- levels on-the-fly. I put them under
- <code>/e/netsw/.www/</code> as follows:</p>
-
-<div class="example"><pre>
--rw-r--r-- 1 netsw users 1318 Aug 1 18:10 .wwwacl
-drwxr-xr-x 18 netsw users 512 Aug 5 15:51 DATA/
--rw-rw-rw- 1 netsw users 372982 Aug 5 16:35 LOGFILE
--rw-r--r-- 1 netsw users 659 Aug 4 09:27 TODO
--rw-r--r-- 1 netsw users 5697 Aug 1 18:01 netsw-about.html
--rwxr-xr-x 1 netsw users 579 Aug 2 10:33 netsw-access.pl
--rwxr-xr-x 1 netsw users 1532 Aug 1 17:35 netsw-changes.cgi
--rwxr-xr-x 1 netsw users 2866 Aug 5 14:49 netsw-home.cgi
-drwxr-xr-x 2 netsw users 512 Jul 8 23:47 netsw-img/
--rwxr-xr-x 1 netsw users 24050 Aug 5 15:49 netsw-lsdir.cgi
--rwxr-xr-x 1 netsw users 1589 Aug 3 18:43 netsw-search.cgi
--rwxr-xr-x 1 netsw users 1885 Aug 1 17:41 netsw-tree.cgi
--rw-r--r-- 1 netsw users 234 Jul 30 16:35 netsw-unlimit.lst
-</pre></div>
-
- <p>The <code>DATA/</code> subdirectory holds the above
- directory structure, <em>i.e.</em> the real
- <strong><em>net.sw</em></strong> stuff, and gets
- automatically updated via <code>rdist</code> from time to
- time. The second part of the problem remains: how to link
- these two structures together into one smooth-looking URL
- tree? We want to hide the <code>DATA/</code> directory
- from the user while running the appropriate CGI scripts
- for the various URLs. Here is the solution: first I put
- the following into the per-directory configuration file
- in the <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code>
- of the server to rewrite the public URL path
- <code>/net.sw/</code> to the internal path
- <code>/e/netsw</code>:</p>
-
-<div class="example"><pre>
-RewriteRule ^net.sw$ net.sw/ [R]
-RewriteRule ^net.sw/(.*)$ e/netsw/$1
-</pre></div>
-
- <p>The first rule is for requests which miss the trailing
- slash! The second rule does the real thing. And then
- comes the killer configuration which stays in the
- per-directory config file
- <code>/e/netsw/.www/.wwwacl</code>:</p>
-
-<div class="example"><pre>
-Options ExecCGI FollowSymLinks Includes MultiViews
-
-RewriteEngine on
-
-# we are reached via /net.sw/ prefix
-RewriteBase /net.sw/
-
-# first we rewrite the root dir to
-# the handling cgi script
-RewriteRule ^$ netsw-home.cgi [L]
-RewriteRule ^index\.html$ netsw-home.cgi [L]
-
-# strip out the subdirs when
-# the browser requests us from perdir pages
-RewriteRule ^.+/(netsw-[^/]+/.+)$ $1 [L]
-
-# and now break the rewriting for local files
-RewriteRule ^netsw-home\.cgi.* - [L]
-RewriteRule ^netsw-changes\.cgi.* - [L]
-RewriteRule ^netsw-search\.cgi.* - [L]
-RewriteRule ^netsw-tree\.cgi$ - [L]
-RewriteRule ^netsw-about\.html$ - [L]
-RewriteRule ^netsw-img/.*$ - [L]
-
-# anything else is a subdir which gets handled
-# by another cgi script
-RewriteRule !^netsw-lsdir\.cgi.* - [C]
-RewriteRule (.*) netsw-lsdir.cgi/$1
-</pre></div>
-
- <p>Some hints for interpretation:</p>
-
- <ol>
- <li>Notice the <code>L</code> (last) flag and no
- substitution field ('<code>-</code>') in the fourth part</li>
-
- <li>Notice the <code>!</code> (not) character and
- the <code>C</code> (chain) flag at the first rule
- in the last part</li>
-
- <li>Notice the catch-all pattern in the last rule</li>
- </ol>
- </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="redirect404" id="redirect404">Redirect Failing URLs to Another Web Server</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>A typical FAQ about URL rewriting is how to redirect
- failing requests on webserver A to webserver B. Usually
- this is done via <code class="directive"><a href="../mod/core.html#errordocument">ErrorDocument</a></code> CGI scripts in Perl, but
- there is also a <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> solution.
- But note that this performs more poorly than using an
- <code class="directive"><a href="../mod/core.html#errordocument">ErrorDocument</a></code>
- CGI script!</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>The first solution has the best performance but less
- flexibility, and is less safe:</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteCond %{DOCUMENT_ROOT/%{REQUEST_URI} <strong>!-f</strong>
-RewriteRule ^(.+) http://<strong>webserverB</strong>.dom/$1
-</pre></div>
-
- <p>The problem here is that this will only work for pages
- inside the <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code>. While you can add more
- Conditions (for instance to also handle homedirs, etc.)
- there is a better variant:</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteCond %{REQUEST_URI} <strong>!-U</strong>
-RewriteRule ^(.+) http://<strong>webserverB</strong>.dom/$1
-</pre></div>
-
- <p>This uses the URL look-ahead feature of <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.
- The result is that this will work for all types of URLs
- and is safe. But it does have a performance impact on
- the web server, because for every request there is one
- more internal subrequest. So, if your web server runs on a
- powerful CPU, use this one. If it is a slow machine, use
- the first approach or better an <code class="directive"><a href="../mod/core.html#errordocument">ErrorDocument</a></code> CGI script.</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="archive-access-multiplexer" id="archive-access-multiplexer">Archive Access Multiplexer</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Do you know the great CPAN (Comprehensive Perl Archive
- Network) under <a href="http://www.perl.com/CPAN">http://www.perl.com/CPAN</a>?
- CPAN automatically redirects browsers to one of many FTP
- servers around the world (generally one near the requesting
- client); each server carries a full CPAN mirror. This is
- effectively an FTP access multiplexing service.
- CPAN runs via CGI scripts, but how could a similar approach
- be implemented via <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>First we notice that as of version 3.0.0,
- <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> can
- also use the "<code>ftp:</code>" scheme on redirects.
- And second, the location approximation can be done by a
- <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>
- over the top-level domain of the client.
- With a tricky chained ruleset we can use this top-level
- domain as a key to our multiplexing map.</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteMap multiplex txt:/path/to/map.cxan
-RewriteRule ^/CxAN/(.*) %{REMOTE_HOST}::$1 [C]
-RewriteRule ^.+\.<strong>([a-zA-Z]+)</strong>::(.*)$ ${multiplex:<strong>$1</strong>|ftp.default.dom}$2 [R,L]
-</pre></div>
-
-<div class="example"><pre>
-##
-## map.cxan -- Multiplexing Map for CxAN
-##
-
-de ftp://ftp.cxan.de/CxAN/
-uk ftp://ftp.cxan.uk/CxAN/
-com ftp://ftp.cxan.com/CxAN/
- :
-##EOF##
-</pre></div>
- </dd>
- </dl>
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="browser-dependent-content" id="browser-dependent-content">Browser Dependent Content</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>At least for important top-level pages it is sometimes
- necessary to provide the optimum of browser dependent
- content, i.e., one has to provide one version for
- current browsers, a different version for the Lynx and text-mode
- browsers, and another for other browsers.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We cannot use content negotiation because the browsers do
- not provide their type in that form. Instead we have to
- act on the HTTP header "User-Agent". The following config
- does the following: If the HTTP header "User-Agent"
- begins with "Mozilla/3", the page <code>foo.html</code>
- is rewritten to <code>foo.NS.html</code> and the
- rewriting stops. If the browser is "Lynx" or "Mozilla" of
- version 1 or 2, the URL becomes <code>foo.20.html</code>.
- All other browsers receive page <code>foo.32.html</code>.
- This is done with the following ruleset:</p>
-
-<div class="example"><pre>
-RewriteCond %{HTTP_USER_AGENT} ^<strong>Mozilla/3</strong>.*
-RewriteRule ^foo\.html$ foo.<strong>NS</strong>.html [<strong>L</strong>]
-
-RewriteCond %{HTTP_USER_AGENT} ^<strong>Lynx/</strong>.* [OR]
-RewriteCond %{HTTP_USER_AGENT} ^<strong>Mozilla/[12]</strong>.*
-RewriteRule ^foo\.html$ foo.<strong>20</strong>.html [<strong>L</strong>]
-
-RewriteRule ^foo\.html$ foo.<strong>32</strong>.html [<strong>L</strong>]
-</pre></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="dynamic-mirror" id="dynamic-mirror">Dynamic Mirror</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Assume there are nice web pages on remote hosts we want
- to bring into our namespace. For FTP servers we would use
- the <code>mirror</code> program which actually maintains an
- explicit up-to-date copy of the remote data on the local
- machine. For a web server we could use the program
- <code>webcopy</code> which runs via HTTP. But both
- techniques have a major drawback: The local copy is
- always only as up-to-date as the last time we ran the program. It
- would be much better if the mirror was not a static one we
- have to establish explicitly. Instead we want a dynamic
- mirror with data which gets updated automatically
- as needed on the remote host(s).</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>To provide this feature we map the remote web page or even
- the complete remote web area to our namespace by the use
- of the <dfn>Proxy Throughput</dfn> feature
- (flag <code>[P]</code>):</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteRule ^<strong>hotsheet/</strong>(.*)$ <strong>http://www.tstimpreso.com/hotsheet/</strong>$1 [<strong>P</strong>]
-</pre></div>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteBase /~quux/
-RewriteRule ^<strong>usa-news\.html</strong>$ <strong>http://www.quux-corp.com/news/index.html</strong> [<strong>P</strong>]
-</pre></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="reverse-dynamic-mirror" id="reverse-dynamic-mirror">Reverse Dynamic Mirror</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>...</dd>
-
- <dt>Solution:</dt>
-
- <dd>
-<div class="example"><pre>
-RewriteEngine on
-RewriteCond /mirror/of/remotesite/$1 -U
-RewriteRule ^http://www\.remotesite\.com/(.*)$ /mirror/of/remotesite/$1
-</pre></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="retrieve-missing-data" id="retrieve-missing-data">Retrieve Missing Data from Intranet</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>This is a tricky way of virtually running a corporate
- (external) Internet web server
- (<code>www.quux-corp.dom</code>), while actually keeping
- and maintaining its data on an (internal) Intranet web server
- (<code>www2.quux-corp.dom</code>) which is protected by a
- firewall. The trick is that the external web server retrieves
- the requested data on-the-fly from the internal
- one.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>First, we must make sure that our firewall still
- protects the internal web server and only the
- external web server is allowed to retrieve data from it.
- On a packet-filtering firewall, for instance, we could
- configure a firewall ruleset like the following:</p>
-
-<div class="example"><pre>
-<strong>ALLOW</strong> Host www.quux-corp.dom Port >1024 --> Host www2.quux-corp.dom Port <strong>80</strong>
-<strong>DENY</strong> Host * Port * --> Host www2.quux-corp.dom Port <strong>80</strong>
-</pre></div>
-
- <p>Just adjust it to your actual configuration syntax.
- Now we can establish the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
- rules which request the missing data in the background
- through the proxy throughput feature:</p>
-
-<div class="example"><pre>
-RewriteRule ^/~([^/]+)/?(.*) /home/$1/.www/$2 [C]
-# REQUEST_FILENAME usage below is correct in this per-server context example
-# because the rule that references REQUEST_FILENAME is chained to a rule that
-# sets REQUEST_FILENAME.
-RewriteCond %{REQUEST_FILENAME} <strong>!-f</strong>
-RewriteCond %{REQUEST_FILENAME} <strong>!-d</strong>
-RewriteRule ^/home/([^/]+)/.www/?(.*) http://<strong>www2</strong>.quux-corp.dom/~$1/pub/$2 [<strong>P</strong>]
-</pre></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="load-balancing" id="load-balancing">Load Balancing</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Suppose we want to load balance the traffic to
- <code>www.example.com</code> over <code>www[0-5].example.com</code>
- (a total of 6 servers). How can this be done?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>There are many possible solutions for this problem.
- We will first discuss a common DNS-based method,
- and then one based on <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>:</p>
-
- <ol>
- <li>
- <strong>DNS Round-Robin</strong>
-
- <p>The simplest method for load-balancing is to use
- DNS round-robin.
- Here you just configure <code>www[0-9].example.com</code>
- as usual in your DNS with A (address) records, e.g.,</p>
-
-<div class="example"><pre>
-www0 IN A 1.2.3.1
-www1 IN A 1.2.3.2
-www2 IN A 1.2.3.3
-www3 IN A 1.2.3.4
-www4 IN A 1.2.3.5
-www5 IN A 1.2.3.6
-</pre></div>
-
- <p>Then you additionally add the following entries:</p>
-
-<div class="example"><pre>
-www IN A 1.2.3.1
-www IN A 1.2.3.2
-www IN A 1.2.3.3
-www IN A 1.2.3.4
-www IN A 1.2.3.5
-</pre></div>
-
- <p>Now when <code>www.example.com</code> gets
- resolved, <code>BIND</code> gives out <code>www0-www5</code>
- - but in a permutated (rotated) order every time.
- This way the clients are spread over the various
- servers. But notice that this is not a perfect load
- balancing scheme, because DNS resolutions are
- cached by clients and other nameservers, so
- once a client has resolved <code>www.example.com</code>
- to a particular <code>wwwN.example.com</code>, all its
- subsequent requests will continue to go to the same
- IP (and thus a single server), rather than being
- distributed across the other available servers. But the
- overall result is
- okay because the requests are collectively
- spread over the various web servers.</p>
- </li>
-
- <li>
- <strong>DNS Load-Balancing</strong>
-
- <p>A sophisticated DNS-based method for
- load-balancing is to use the program
- <code>lbnamed</code> which can be found at <a href="http://www.stanford.edu/~riepel/lbnamed/">
- http://www.stanford.edu/~riepel/lbnamed/</a>.
- It is a Perl 5 program which, in conjunction with auxiliary
- tools, provides real load-balancing via
- DNS.</p>
- </li>
-
- <li>
- <strong>Proxy Throughput Round-Robin</strong>
-
- <p>In this variant we use <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
- and its proxy throughput feature. First we dedicate
- <code>www0.example.com</code> to be actually
- <code>www.example.com</code> by using a single</p>
-
-<div class="example"><pre>
-www IN CNAME www0.example.com.
-</pre></div>
-
- <p>entry in the DNS. Then we convert
- <code>www0.example.com</code> to a proxy-only server,
- i.e., we configure this machine so all arriving URLs
- are simply passed through its internal proxy to one of
- the 5 other servers (<code>www1-www5</code>). To
- accomplish this we first establish a ruleset which
- contacts a load balancing script <code>lb.pl</code>
- for all URLs.</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteMap lb prg:/path/to/lb.pl
-RewriteRule ^/(.+)$ ${lb:$1} [P,L]
-</pre></div>
-
- <p>Then we write <code>lb.pl</code>:</p>
-
-<div class="example"><pre>
-#!/path/to/perl
-##
-## lb.pl -- load balancing script
-##
-
-$| = 1;
-
-$name = "www"; # the hostname base
-$first = 1; # the first server (not 0 here, because 0 is myself)
-$last = 5; # the last server in the round-robin
-$domain = "foo.dom"; # the domainname
-
-$cnt = 0;
-while (<STDIN>) {
- $cnt = (($cnt+1) % ($last+1-$first));
- $server = sprintf("%s%d.%s", $name, $cnt+$first, $domain);
- print "http://$server/$_";
-}
-
-##EOF##
-</pre></div>
-
- <div class="note">A last notice: Why is this useful? Seems like
- <code>www0.example.com</code> still is overloaded? The
- answer is yes, it is overloaded, but with plain proxy
- throughput requests, only! All SSI, CGI, ePerl, etc.
- processing is handled done on the other machines.
- For a complicated site, this may work well. The biggest
- risk here is that www0 is now a single point of failure --
- if it crashes, the other servers are inaccessible.</div>
- </li>
-
- <li>
- <strong>Dedicated Load Balancers</strong>
-
- <p>There are more sophisticated solutions, as well. Cisco,
- F5, and several other companies sell hardware load
- balancers (typically used in pairs for redundancy), which
- offer sophisticated load balancing and auto-failover
- features. There are software packages which offer similar
- features on commodity hardware, as well. If you have
- enough money or need, check these out. The <a href="http://vegan.net/lb/">lb-l mailing list</a> is a
- good place to research.</p>
- </li>
- </ol>
- </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="new-mime-type" id="new-mime-type">New MIME-type, New Service</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>On the net there are many nifty CGI programs. But
- their usage is usually boring, so a lot of webmasters
- don't use them. Even Apache's Action handler feature for
- MIME-types is only appropriate when the CGI programs
- don't need special URLs (actually <code>PATH_INFO</code>
- and <code>QUERY_STRINGS</code>) as their input. First,
- let us configure a new file type with extension
- <code>.scgi</code> (for secure CGI) which will be processed
- by the popular <code>cgiwrap</code> program. The problem
- here is that for instance if we use a Homogeneous URL Layout
- (see above) a file inside the user homedirs might have a URL
- like <code>/u/user/foo/bar.scgi</code>, but
- <code>cgiwrap</code> needs URLs in the form
- <code>/~user/foo/bar.scgi/</code>. The following rule
- solves the problem:</p>
-
-<div class="example"><pre>
-RewriteRule ^/[uge]/<strong>([^/]+)</strong>/\.www/(.+)\.scgi(.*) ...
-... /internal/cgi/user/cgiwrap/~<strong>$1</strong>/$2.scgi$3 [NS,<strong>T=application/x-http-cgi</strong>]
-</pre></div>
-
- <p>Or assume we have some more nifty programs:
- <code>wwwlog</code> (which displays the
- <code>access.log</code> for a URL subtree) and
- <code>wwwidx</code> (which runs Glimpse on a URL
- subtree). We have to provide the URL area to these
- programs so they know which area they are really working with.
- But usually this is complicated, because they may still be
- requested by the alternate URL form, i.e., typically we would
- run the <code>swwidx</code> program from within
- <code>/u/user/foo/</code> via hyperlink to</p>
-
-<div class="example"><pre>
-/internal/cgi/user/swwidx?i=/u/user/foo/
-</pre></div>
-
- <p>which is ugly, because we have to hard-code
- <strong>both</strong> the location of the area
- <strong>and</strong> the location of the CGI inside the
- hyperlink. When we have to reorganize, we spend a
- lot of time changing the various hyperlinks.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>The solution here is to provide a special new URL format
- which automatically leads to the proper CGI invocation.
- We configure the following:</p>
-
-<div class="example"><pre>
-RewriteRule ^/([uge])/([^/]+)(/?.*)/\* /internal/cgi/user/wwwidx?i=/$1/$2$3/
-RewriteRule ^/([uge])/([^/]+)(/?.*):log /internal/cgi/user/wwwlog?f=/$1/$2$3
-</pre></div>
-
- <p>Now the hyperlink to search at
- <code>/u/user/foo/</code> reads only</p>
-
-<div class="example"><pre>
-HREF="*"
-</pre></div>
-
- <p>which internally gets automatically transformed to</p>
-
-<div class="example"><pre>
-/internal/cgi/user/wwwidx?i=/u/user/foo/
-</pre></div>
-
- <p>The same approach leads to an invocation for the
- access log CGI program when the hyperlink
- <code>:log</code> gets used.</p>
- </dd>
- </dl>
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="on-the-fly-content" id="on-the-fly-content">On-the-fly Content-Regeneration</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Here comes a really esoteric feature: Dynamically
- generated but statically served pages, i.e., pages should be
- delivered as pure static pages (read from the filesystem
- and just passed through), but they have to be generated
- dynamically by the web server if missing. This way you can
- have CGI-generated pages which are statically served unless an
- admin (or a <code>cron</code> job) removes the static contents. Then the
- contents gets refreshed.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- This is done via the following ruleset:
-
-<div class="example"><pre>
-# This example is valid in per-directory context only
-RewriteCond %{REQUEST_FILENAME} <strong>!-s</strong>
-RewriteRule ^page\.<strong>html</strong>$ page.<strong>cgi</strong> [T=application/x-httpd-cgi,L]
-</pre></div>
-
- <p>Here a request for <code>page.html</code> leads to an
- internal run of a corresponding <code>page.cgi</code> if
- <code>page.html</code> is missing or has filesize
- null. The trick here is that <code>page.cgi</code> is a
- CGI script which (additionally to its <code>STDOUT</code>)
- writes its output to the file <code>page.html</code>.
- Once it has completed, the server sends out
- <code>page.html</code>. When the webmaster wants to force
- a refresh of the contents, he just removes
- <code>page.html</code> (typically from <code>cron</code>).</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="autorefresh" id="autorefresh">Document With Autorefresh</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Wouldn't it be nice, while creating a complex web page, if
- the web browser would automatically refresh the page every
- time we save a new version from within our editor?
- Impossible?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>No! We just combine the MIME multipart feature, the
- web server NPH feature, and the URL manipulation power of
- <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>. First, we establish a new
- URL feature: Adding just <code>:refresh</code> to any
- URL causes the 'page' to be refreshed every time it is
- updated on the filesystem.</p>
-
-<div class="example"><pre>
-RewriteRule ^(/[uge]/[^/]+/?.*):refresh /internal/cgi/apache/nph-refresh?f=$1
-</pre></div>
-
- <p>Now when we reference the URL</p>
-
-<div class="example"><pre>
-/u/foo/bar/page.html:refresh
-</pre></div>
-
- <p>this leads to the internal invocation of the URL</p>
-
-<div class="example"><pre>
-/internal/cgi/apache/nph-refresh?f=/u/foo/bar/page.html
-</pre></div>
-
- <p>The only missing part is the NPH-CGI script. Although
- one would usually say "left as an exercise to the reader"
- ;-) I will provide this, too.</p>
-
-<div class="example"><pre>
-#!/sw/bin/perl
-##
-## nph-refresh -- NPH/CGI script for auto refreshing pages
-## Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved.
-##
-$| = 1;
-
-# split the QUERY_STRING variable
-@pairs = split(/&/, $ENV{'QUERY_STRING'});
-foreach $pair (@pairs) {
- ($name, $value) = split(/=/, $pair);
- $name =~ tr/A-Z/a-z/;
- $name = 'QS_' . $name;
- $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg;
- eval "\$$name = \"$value\"";
-}
-$QS_s = 1 if ($QS_s eq '');
-$QS_n = 3600 if ($QS_n eq '');
-if ($QS_f eq '') {
- print "HTTP/1.0 200 OK\n";
- print "Content-type: text/html\n\n";
- print "&lt;b&gt;ERROR&lt;/b&gt;: No file given\n";
- exit(0);
-}
-if (! -f $QS_f) {
- print "HTTP/1.0 200 OK\n";
- print "Content-type: text/html\n\n";
- print "&lt;b&gt;ERROR&lt;/b&gt;: File $QS_f not found\n";
- exit(0);
-}
-
-sub print_http_headers_multipart_begin {
- print "HTTP/1.0 200 OK\n";
- $bound = "ThisRandomString12345";
- print "Content-type: multipart/x-mixed-replace;boundary=$bound\n";
- &print_http_headers_multipart_next;
-}
-
-sub print_http_headers_multipart_next {
- print "\n--$bound\n";
-}
-
-sub print_http_headers_multipart_end {
- print "\n--$bound--\n";
-}
-
-sub displayhtml {
- local($buffer) = @_;
- $len = length($buffer);
- print "Content-type: text/html\n";
- print "Content-length: $len\n\n";
- print $buffer;
-}
-
-sub readfile {
- local($file) = @_;
- local(*FP, $size, $buffer, $bytes);
- ($x, $x, $x, $x, $x, $x, $x, $size) = stat($file);
- $size = sprintf("%d", $size);
- open(FP, "&lt;$file");
- $bytes = sysread(FP, $buffer, $size);
- close(FP);
- return $buffer;
-}
-
-$buffer = &readfile($QS_f);
-&print_http_headers_multipart_begin;
-&displayhtml($buffer);
-
-sub mystat {
- local($file) = $_[0];
- local($time);
-
- ($x, $x, $x, $x, $x, $x, $x, $x, $x, $mtime) = stat($file);
- return $mtime;
-}
-
-$mtimeL = &mystat($QS_f);
-$mtime = $mtime;
-for ($n = 0; $n &lt; $QS_n; $n++) {
- while (1) {
- $mtime = &mystat($QS_f);
- if ($mtime ne $mtimeL) {
- $mtimeL = $mtime;
- sleep(2);
- $buffer = &readfile($QS_f);
- &print_http_headers_multipart_next;
- &displayhtml($buffer);
- sleep(5);
- $mtimeL = &mystat($QS_f);
- last;
- }
- sleep($QS_s);
- }
-}
-
-&print_http_headers_multipart_end;
-
-exit(0);
-
-##EOF##
-</pre></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="mass-virtual-hosting" id="mass-virtual-hosting">Mass Virtual Hosting</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>The <code class="directive"><a href="../mod/core.html#virtualhost"><VirtualHost></a></code> feature of Apache is nice
- and works great when you just have a few dozen
- virtual hosts. But when you are an ISP and have hundreds of
- virtual hosts, this feature is suboptimal.</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>To provide this feature we map the remote web page or even
- the complete remote web area to our namespace using the
- <dfn>Proxy Throughput</dfn> feature (flag <code>[P]</code>):</p>
-
-<div class="example"><pre>
-##
-## vhost.map
-##
-www.vhost1.dom:80 /path/to/docroot/vhost1
-www.vhost2.dom:80 /path/to/docroot/vhost2
- :
-www.vhostN.dom:80 /path/to/docroot/vhostN
-</pre></div>
-
-<div class="example"><pre>
-##
-## httpd.conf
-##
- :
-# use the canonical hostname on redirects, etc.
-UseCanonicalName on
-
- :
-# add the virtual host in front of the CLF-format
-CustomLog /path/to/access_log "%{VHOST}e %h %l %u %t \"%r\" %>s %b"
- :
-
-# enable the rewriting engine in the main server
-RewriteEngine on
-
-# define two maps: one for fixing the URL and one which defines
-# the available virtual hosts with their corresponding
-# DocumentRoot.
-RewriteMap lowercase int:tolower
-RewriteMap vhost txt:/path/to/vhost.map
-
-# Now do the actual virtual host mapping
-# via a huge and complicated single rule:
-#
-# 1. make sure we don't map for common locations
-RewriteCond %{REQUEST_URI} !^/commonurl1/.*
-RewriteCond %{REQUEST_URI} !^/commonurl2/.*
- :
-RewriteCond %{REQUEST_URI} !^/commonurlN/.*
-#
-# 2. make sure we have a Host header, because
-# currently our approach only supports
-# virtual hosting through this header
-RewriteCond %{HTTP_HOST} !^$
-#
-# 3. lowercase the hostname
-RewriteCond ${lowercase:%{HTTP_HOST}|NONE} ^(.+)$
-#
-# 4. lookup this hostname in vhost.map and
-# remember it only when it is a path
-# (and not "NONE" from above)
-RewriteCond ${vhost:%1} ^(/.*)$
-#
-# 5. finally we can map the URL to its docroot location
-# and remember the virtual host for logging purposes
-RewriteRule ^/(.*)$ %1/$1 [E=VHOST:${lowercase:%{HTTP_HOST}}]
- :
-</pre></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="host-deny" id="host-deny">Host Deny</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>How can we forbid a list of externally configured hosts
- from using our server?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>For Apache >= 1.3b6:</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteMap hosts-deny txt:/path/to/hosts.deny
-RewriteCond ${hosts-deny:%{REMOTE_HOST}|NOT-FOUND} !=NOT-FOUND [OR]
-RewriteCond ${hosts-deny:%{REMOTE_ADDR}|NOT-FOUND} !=NOT-FOUND
-RewriteRule ^/.* - [F]
-</pre></div>
-
- <p>For Apache <= 1.3b6:</p>
-
-<div class="example"><pre>
-RewriteEngine on
-RewriteMap hosts-deny txt:/path/to/hosts.deny
-RewriteRule ^/(.*)$ ${hosts-deny:%{REMOTE_HOST}|NOT-FOUND}/$1
-RewriteRule !^NOT-FOUND/.* - [F]
-RewriteRule ^NOT-FOUND/(.*)$ ${hosts-deny:%{REMOTE_ADDR}|NOT-FOUND}/$1
-RewriteRule !^NOT-FOUND/.* - [F]
-RewriteRule ^NOT-FOUND/(.*)$ /$1
-</pre></div>
-
-<div class="example"><pre>
-##
-## hosts.deny
-##
-## ATTENTION! This is a map, not a list, even when we treat it as such.
-## mod_rewrite parses it for key/value pairs, so at least a
-## dummy value "-" must be present for each entry.
-##
-
-193.102.180.41 -
-bsdti1.sdm.de -
-192.76.162.40 -
-</pre></div>
- </dd>
- </dl>
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="proxy-deny" id="proxy-deny">Proxy Deny</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>How can we forbid a certain host or even a user of a
- special host from using the Apache proxy?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We first have to make sure <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
- is below(!) <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code> in the Configuration
- file when compiling the Apache web server. This way it gets
- called <em>before</em> <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code>. Then we
- configure the following for a host-dependent deny...</p>
-
-<div class="example"><pre>
-RewriteCond %{REMOTE_HOST} <strong>^badhost\.mydomain\.com$</strong>
-RewriteRule !^http://[^/.]\.mydomain.com.* - [F]
-</pre></div>
-
- <p>...and this one for a user@host-dependent deny:</p>
-
-<div class="example"><pre>
-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>^badguy@badhost\.mydomain\.com$</strong>
-RewriteRule !^http://[^/.]\.mydomain.com.* - [F]
-</pre></div>
- </dd>
- </dl>
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="special-authentication" id="special-authentication">Special Authentication Variant</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>Sometimes very special authentication is needed, for
- instance authentication which checks for a set of
- explicitly configured users. Only these should receive
- access and without explicit prompting (which would occur
- when using Basic Auth via <code class="module"><a href="../mod/mod_auth_basic.html">mod_auth_basic</a></code>).</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>We use a list of rewrite conditions to exclude all except
- our friends:</p>
-
-<div class="example"><pre>
-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>!^friend1@client1.quux-corp\.com$</strong>
-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>!^friend2</strong>@client2.quux-corp\.com$
-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>!^friend3</strong>@client3.quux-corp\.com$
-RewriteRule ^/~quux/only-for-friends/ - [F]
-</pre></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="referer-deflector" id="referer-deflector">Referer-based Deflector</a></h2>
-
-
-
- <dl>
- <dt>Description:</dt>
-
- <dd>
- <p>How can we program a flexible URL Deflector which acts
- on the "Referer" HTTP header and can be configured with as
- many referring pages as we like?</p>
- </dd>
-
- <dt>Solution:</dt>
-
- <dd>
- <p>Use the following really tricky ruleset...</p>
-
-<div class="example"><pre>
-RewriteMap deflector txt:/path/to/deflector.map
-
-RewriteCond %{HTTP_REFERER} !=""
-RewriteCond ${deflector:%{HTTP_REFERER}} ^-$
-RewriteRule ^.* %{HTTP_REFERER} [R,L]
-
-RewriteCond %{HTTP_REFERER} !=""
-RewriteCond ${deflector:%{HTTP_REFERER}|NOT-FOUND} !=NOT-FOUND
-RewriteRule ^.* ${deflector:%{HTTP_REFERER}} [R,L]
-</pre></div>
-
- <p>... in conjunction with a corresponding rewrite
- map:</p>
-
-<div class="example"><pre>
-##
-## deflector.map
-##
-
-http://www.badguys.com/bad/index.html -
-http://www.badguys.com/bad/index2.html -
-http://www.badguys.com/bad/index3.html http://somewhere.com/
-</pre></div>
-
- <p>This automatically redirects the request back to the
- referring page (when "<code>-</code>" is used as the value
- in the map) or to a specific URL (when an URL is specified
- in the map as the second argument).</p>
- </dd>
- </dl>
-
- </div></div>
+</div>
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