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<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head>
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<meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type" />
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              This file is generated from xml source: DO NOT EDIT
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      -->
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<title>Advanced Techniques with mod_rewrite - Apache HTTP Server Version 2.4</title>
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<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
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</script>
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<link href="../images/favicon.ico" rel="shortcut icon" /></head>
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<body id="manual-page">
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Modules | Directives | FAQ | Glossary | Sitemap
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Apache HTTP Server Version 2.4
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<-
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Apache > HTTP Server > Documentation > Version 2.4 > Rewrite
Advanced Techniques with mod_rewrite
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Available Languages:  en  |
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 fr 
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This document supplements the mod_rewrite
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reference documentation. It provides
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a few advanced techniques using mod_rewrite.
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Note that many of these examples won't work unchanged in your
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particular server configuration, so it's important that you understand
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them, rather than merely cutting and pasting the examples into your
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configuration.
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  •  On-the-fly Content-Regeneration
    		•
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  •  Load Balancing
    		•
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  •  Structured Userdirs
    		•
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  •  Redirecting Anchors
    		•
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  •  Time-Dependent Rewriting
    		•
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  •  Set Environment Variables Based On URL Parts
    		•
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    See also
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    top
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    URL-based sharding across multiple backends
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    Description:
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    A common technique for distributing the burden of
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          server load or storage space is called "sharding".
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          When using this method, a front-end server will use the
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          url to consistently "shard" users or objects to separate
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          backend servers.
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    Solution:
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    A mapping is maintained, from users to target servers, in
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          external map files. They look like:
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    user1  physical_host_of_user1
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    user2  physical_host_of_user2
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    :      :
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    We put this into a map.users-to-hosts file. The
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        aim is to map;
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    /u/user1/anypath
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    to
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    http://physical_host_of_user1/u/user/anypath
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    thus every URL path need not be valid on every backend physical
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          host. The following ruleset does this for us with the help of the map
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          files assuming that server0 is a default server which will be used if
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          a user has no entry in the map:
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    RewriteEngine on
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    RewriteMap      users-to-hosts   "txt:/path/to/map.users-to-hosts"
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    RewriteRule   "^/u/([^/]+)/?(.*)"   "http://${users-to-hosts:$1|server0}/u/$1/$2"
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    See the RewriteMap
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      documentation for more discussion of the syntax of this directive.
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    On-the-fly Content-Regeneration
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    Description:
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    We wish to dynamically generate content, but store it
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          statically once it is generated. This rule will check for the
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          existence of the static file, and if it's not there, generate
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          it. The static files can be removed periodically, if desired (say,
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          via cron) and will be regenerated on demand.
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    Solution:
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          This is done via the following ruleset:
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    # This example is valid in per-directory context only
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    RewriteCond "%{REQUEST_URI}"   "!-U"
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    RewriteRule "^(.+)\.html$"          "/regenerate_page.cgi"   [PT,L]
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    The -U operator determines whether the test string
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        (in this case, REQUEST_URI) is a valid URL. It does
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        this via a subrequest. In the event that this subrequest fails -
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        that is, the requested resource doesn't exist - this rule invokes
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        the CGI program /regenerate_page.cgi, which generates
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        the requested resource and saves it into the document directory, so
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        that the next time it is requested, a static copy can be served.
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    In this way, documents that are infrequently updated can be served in
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        static form. if documents need to be refreshed, they can be deleted
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        from the document directory, and they will then be regenerated the
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        next time they are requested.
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    Load Balancing
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    Description:
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    We wish to randomly distribute load across several servers
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          using mod_rewrite.
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    Solution:
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    We'll use RewriteMap and a list of servers
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          to accomplish this.
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    RewriteEngine on
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    RewriteMap lb "rnd:/path/to/serverlist.txt"
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    RewriteRule "^/(.*)" "http://${lb:servers}/$1" [P,L]
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    serverlist.txt will contain a list of the servers:
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    ## serverlist.txt
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    servers one.example.com|two.example.com|three.example.com
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    If you want one particular server to get more of the load than the
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    others, add it more times to the list.
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    Discussion
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    Apache comes with a load-balancing module -
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    mod_proxy_balancer - which is far more flexible and
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    featureful than anything you can cobble together using mod_rewrite.
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    top
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    Structured Userdirs
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    Description:
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    Some sites with thousands of users use a
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          structured homedir layout, i.e. each homedir is in a
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          subdirectory which begins (for instance) with the first
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          character of the username. So, /~larry/anypath
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          is /home/l/larry/public_html/anypath
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          while /~waldo/anypath is
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          /home/w/waldo/public_html/anypath.
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    Solution:
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    We use the following ruleset to expand the tilde URLs
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          into the above layout.
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    RewriteEngine on
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    RewriteRule   "^/~(([a-z])[a-z0-9]+)(.*)"  "/home/$2/$1/public_html$3"
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    Redirecting Anchors
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    Description:
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    By default, redirecting to an HTML anchor doesn't work,
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        because mod_rewrite escapes the # character,
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        turning it into %23. This, in turn, breaks the
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        redirection.
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    Solution:
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    Use the [NE] flag on the
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          RewriteRule. NE stands for No Escape.
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    Discussion:
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    This technique will of course also work with other
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        special characters that mod_rewrite, by default, URL-encodes.
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    Time-Dependent Rewriting
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    Description:
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    We wish to use mod_rewrite to serve different content based on
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          the time of day.
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    Solution:
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    There are a lot of variables named TIME_xxx
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          for rewrite conditions. In conjunction with the special
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          lexicographic comparison patterns <STRING,
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          >STRING and =STRING we can
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          do time-dependent redirects:
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    RewriteEngine on
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    RewriteCond   "%{TIME_HOUR}%{TIME_MIN}" ">0700"
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    RewriteCond   "%{TIME_HOUR}%{TIME_MIN}" "<1900"
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    RewriteRule   "^foo\.html$"             "foo.day.html" [L]
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    RewriteRule   "^foo\.html$"             "foo.night.html"
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    This provides the content of foo.day.html
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          under the URL foo.html from
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          07:01-18:59 and at the remaining time the
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          contents of foo.night.html.
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    mod_cache, intermediate proxies
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          and browsers may each cache responses and cause the either page to be
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          shown outside of the time-window configured.
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          mod_expires may be used to control this
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          effect. You are, of course, much better off simply serving the
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          content dynamically, and customizing it based on the time of day.
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    top
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    Set Environment Variables Based On URL Parts
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    Description:
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    At time, we want to maintain some kind of status when we
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          perform a rewrite. For example, you want to make a note that
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          you've done that rewrite, so that you can check later to see if a
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          request can via that rewrite. One way to do this is by setting an
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          environment variable.
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    Solution:
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    Use the [E] flag to set an environment variable.
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    RewriteEngine on
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    RewriteRule   "^/horse/(.*)"   "/pony/$1" [E=rewritten:1]
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    Later in your ruleset you might check for this environment
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        variable using a RewriteCond:
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    RewriteCond "%{ENV:rewritten}" "=1"
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    Note that environment variables do not survive an external
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        redirect. You might consider using the [CO] flag to set a
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        cookie.
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    Available Languages:  en  |
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     fr 
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    top
    Comments
    Notice:
    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 mailing lists.
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    Copyright 2018 The Apache Software Foundation.
    Licensed under the Apache License, Version 2.0.
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    Modules | Directives | FAQ | Glossary | Sitemap
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