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| <manualpage metafile="avoid.xml.meta"> |
| <parentdocument href="./">Rewrite</parentdocument> |
| |
| <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 <module>mod_rewrite</module> - namely, |
| when to avoid using it.</p> |
| |
| <p><module>mod_rewrite</module> 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 <module>mod_rewrite</module> 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> |
| <!--<seealso><a href="avoid.html">When not to use mod_rewrite</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 one hostname to another, for example |
| <code>example.com</code> to <code>www.example.com</code>, see the |
| <a href="remapping.html#canonicalhost">Canonical Hostnames</a> |
| recipe.</p> |
| |
| <p>To redirect <code>http</code> URLs to <code>https</code>, do the |
| following:</p> |
| |
| <highlight language="config"> |
| <VirtualHost *:80> |
| ServerName www.example.com |
| Redirect "/" "https://www.example.com/" |
| </VirtualHost> |
| |
| <VirtualHost *:443> |
| ServerName www.example.com |
| # ... SSL configuration goes here |
| </VirtualHost> |
| </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 <module>mod_rewrite</module>, |
| <directive module="mod_alias">Alias</directive> 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 <module>mod_rewrite</module> 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 |
| <directive module="core" type="section">VirtualHost</directive> 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>Modules such as <module>mod_macro</module> 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><directive module="mod_rewrite">RewriteRule</directive> 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"> |
| <If "req('Host') != 'www.example.com'"> |
| Redirect "/" "http://www.example.com/" |
| </If> |
| </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 <directive module="core" type="section">If</directive> sections, |
| and in certain other directives.</p> |
| |
| </section> |
| |
| </manualpage> |
| |