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<title>When not to use mod_rewrite</title>

<summary>

<p>This document supplements the <module>mod_rewrite</module>

<a href="/mod/mod_rewrite.html">reference documentation</a>. It describes

perhaps one of the most important concepts about mod_rewrite - namely,

when to avoid using it.</p>

<p>mod_rewrite should be considered a last resort, when other

alternatives are found wanting. Using it when there are simpler

alternatives leads to configurations which are confusing, fragile, and

hard to maintain. Understanding what other alternatives are available is

a very important step towards mod_rewrite mastery.</p>

<p>Note that many of these examples won't work unchanged in your

particular server configuration, so it's important that you understand

them, rather than merely cutting and pasting the examples into your

configuration.</p>

<p>The most common situation in which <module>mod_rewrite</module> is

the right tool is when the very best solution requires access to the

server configuration files, and you don't have that access. Some

configuration directives are only available in the server configuration

file. So if you are in a hosting situation where you only have .htaccess

files to work with, you may need to resort to

<module>mod_rewrite</module>.</p>

</summary>

<seealso><a href="/mod/mod_rewrite.html">Module documentation</a></seealso>

<seealso><a href="intro.html">mod_rewrite introduction</a></seealso>

<seealso><a href="remapping.html">Redirection and remapping</a></seealso>

<seealso><a href="access.html">Controlling access</a></seealso>

<seealso><a href="vhosts.html">Virtual hosts</a></seealso>

<seealso><a href="proxy.html">Proxying</a></seealso>

<seealso><a href="rewritemap.html">Using RewriteMap</a></seealso>

<seealso><a href="advanced.html">Advanced techniques</a></seealso>

<section id="redirect">

<title>Simple Redirection</title>

<p><module>mod_alias</module> provides the <directive

module="mod_alias">Redirect</directive> and <directive

module="mod_alias">RedirectMatch</directive> directives, which provide a

means to redirect one URL to another. This kind of simple redirection of

one URL, or a class of URLs, to somewhere else, should be accomplished

using these directives rather than <directive

module="mod_rewrite">RewriteRule</directive>. <code>RedirectMatch</code>

allows you to include a regular expression in your redirection criteria,

providing many of the benefits of using <code>RewriteRule</code>.</p>

<p>A common use for <code>RewriteRule</code> is to redirect an entire

class of URLs. For example, all URLs in the <code>/one</code> directory

must be redirected to <code>http://one.example.com/</code>, or perhaps

all <code>http</code> requests must be redirected to

<code>https</code>.</p>

<p>These situations are better handled by the <code>Redirect</code>

directive. Remember that <code>Redirect</code> preserves path

information. That is to say, a redirect for a URL <code>/one</code> will

also redirect all URLs under that, such as <code>/one/two.html</code>

and <code>/one/three/four.html</code>.</p>

<p>To redirect URLs under <code>/one</code> to

<code>http://one.example.com</code>, do the following:</p>

<highlight language="config">Redirect /one/ http://one.example.com/</highlight>

<p>To redirect <code>http</code> URLs to <code>https</code>, do the

following:</p>

<highlight language="config">

&lt;VirtualHost *:80&gt;

ServerName www.example.com

Redirect / https://www.example.com/

&lt;/VirtualHost &gt;

&lt;VirtualHost *:443&gt;

ServerName www.example.com

# ... SSL configuration goes here

&lt;/VirtualHost &gt;

</highlight>

<p>The use of <code>RewriteRule</code> to perform this task may be

appropriate if there are other <code>RewriteRule</code> directives in

the same scope. This is because, when there are <code>Redirect</code>

and <code>RewriteRule</code> directives in the same scope, the

<code>RewriteRule</code> directives will run first, regardless of the

order of appearance in the configuration file.</p>

<p>In the case of the <em>http-to-https</em> redirection, the use of

<code>RewriteRule</code> would be appropriate if you don't have access

to the main server configuration file, and are obliged to perform this

task in a <code>.htaccess</code> file instead.</p>

</section>

<section id="alias"><title>URL Aliasing</title>

<p>The <directive module="mod_alias">Alias</directive> directive

provides mapping from a URI to a directory - usually a directory outside

of your <directive module="core">DocumentRoot</directive>. Although it

is possible to perform this mapping with <code>mod_rewrite</code>,

<code>Alias</code> is the preferred method, for reasons of simplicity

and performance.</p>

<example><title>Using Alias</title>

<highlight language="config">Alias /cats /var/www/virtualhosts/felines/htdocs</highlight>

</example>

<p>

The use of <code>mod_rewrite</code> to perform this mapping may be

appropriate when you do not have access to the server configuration

files. Alias may only be used in server or virtualhost context, and not

in a <code>.htaccess</code> file.

</p>

<p>Symbolic links would be another way to accomplish the same thing, if

you have <code>Options FollowSymLinks</code> enabled on your

server.</p>

</section>

<section id="vhosts"><title>Virtual Hosting</title>

<p>Although it is possible to handle <a href="vhosts.html">virtual hosts

with mod_rewrite</a>, it is seldom the right way. Creating individual

&lt;VirtualHost&gt; blocks is almost always the right way to go. In the

event that you have an enormous number of virtual hosts, consider using

<module>mod_vhost_alias</module> to create these hosts automatically.</p>

<p>Third-party modules such as <a href="http://www.cri.ensmp.fr/~coelho/mod_macro/">mod_macro</a> are

also useful for creating a large number of virtual hosts dynamically.</p>

<p>Using <module>mod_rewrite</module> for vitualhost creation may be

appropriate if you are using a hosting service that does not provide

you access to the server configuration files, and you are therefore

restricted to configuration using <code>.htaccess</code> files.</p>

<p>See the <a href="vhosts.html">virtual hosts with mod_rewrite</a>

document for more details on how you might accomplish this if it still

seems like the right approach.</p>

</section>

<section id="proxy"><title>Simple Proxying</title>

<p><code>RewriteRule</code> provides the <a

href="flags.html#flag_p">[P]</a> flag to pass rewritten URIs through

<module>mod_proxy</module>.</p>

<highlight language="config">

RewriteRule ^/?images(.*) http://imageserver.local/images$1 [P]

</highlight>

<p>However, in many cases, when there is no actual pattern matching

needed, as in the example shown above, the <directive

module="mod_proxy">ProxyPass</directive> directive is a better choice.

The example here could be rendered as:</p>

<highlight language="config">

ProxyPass /images/ http://imageserver.local/images/

</highlight>

<p>Note that whether you use <directive

module="mod_rewrite">RewriteRule</directive> or <directive

module="mod_proxy">ProxyPass</directive>, you'll still need to use the

<directive module="mod_proxy">ProxyPassReverse</directive> directive to

catch redirects issued from the back-end server:</p>

<highlight language="config">

ProxyPassReverse /images/ http://imageserver.local/images/

</highlight>

<p>You may need to use <code>RewriteRule</code> instead when there are

other <code>RewriteRule</code>s in effect in the same scope, as a

<code>RewriteRule</code> will usually take effect before a

<code>ProxyPass</code>, and so may preempt what you're trying to

accomplish.</p>

</section>

<section id="setenv"><title>Environment Variable Testing</title>

<p><module>mod_rewrite</module> is frequently used to take a particular

action based on the presence or absence of a particular environment

variable or request header. This can be done more efficiently using the

<directive module="core" type="section">If</directive>.</p>

<p>Consider, for example, the common scenario where

<directive>RewriteRule</directive> is used to enforce a canonical

hostname, such as <code>www.example.com</code> instead of

<code>example.com</code>. This can be done using the <directive

module="core" type="section">If</directive> directive, as shown here:</p>

<highlight language="config">

&lt;If "$req{Host} != 'www.example.com'"&gt;

RedirectMatch (.*) http://www.example.com$1

&lt;/If&gt;

</highlight>

<p>This technique can be used to take actions based on any request

header, response header, or environment variable, replacing

<module>mod_rewrite</module> in many common scenarios.</p>

<p>See especially the <a href="/expr.html">expression evaluation

documentation</a> for a overview of what types of expressions you can

use in &lt;If&gt; sections, and in certain other directives.</p>

</section>

</manualpage>