Using mod_rewrite, RewriteMap to re-arrange website content

When moving differentpla.net from one server to another, I decided to move the content (currently served using drupal) from the root to /content. I also decided to use more descriptive URLs.

But I didn’t want to break too many external links.

Here’s how I used Apache’s mod_rewrite - specifically RewriteMap - to achieve this.

As explained in the linked page, I’ve moved differentpla.net from my Linux box at home to a Virtual Private Server (VPS), hosted in the US.

I’ll also be moving a few other websites from this machine. In order to better implement a shared installation of both Gallery2 and drupal across those websites, I decided to move differentpla.net’s content from the root to a subdirectory.

Along with this, I decided to make use of drupal’s path remapping support to generate more descriptive URLs for the content.

However, I don’t particularly want to break external links to the website, so I looked into using mod_rewrite to help with this.

It turns out that mod_rewrite has a feature called RewriteMap, which does exactly what I want.

To use it, I simply added the following section to /etc/apache2/sites-available/differentpla.net:

<IfModule mod_rewrite.c>
    RewriteEngine on

    RewriteLog /var/log/apache2/rewrite.log
    RewriteLogLevel 0

    # Anything matching /node/X or /node/view/X is remapped
    # via this text file, which is keyed on X
    RewriteMap txtmap txt:/home/www/sites/differentpla.net/map.txt

    RewriteCond %{REQUEST_URI}      ^/node/view/
    RewriteRule ^/node/view/(.*)    /content/${txtmap:$1} [R]

    RewriteCond %{REQUEST_URI}      ^/node/
    RewriteRule ^/node/(.*)         /content/${txtmap:$1} [R]
</IfModule>

It’s enclosed in a condition block, so that it only takes effect if mod_rewrite is enabled.

The first line turns on mod_rewrite. The next two control logging. Level 0 (zero) means that rewrite logging is off.

Then I define the RewriteMap. Currently this is a simple text file. mod_rewrite also has support for other types of data source.

Then there are the two things I want to recognise. There are two different ways to access drupal content. You can go to /node/NNN or /node/view/NNN. These two rules extract the NNN, look it up in the map, prefix it with /content/, and then issue a redirect.

Everything else is passed through unchanged.

Here’s a snippet from map.txt:

1       welcome
10      2002/03/rsync-empegs

So, you can see that /node/1 or /node/view/1 are mapped to /content/welcome; and that /node/10 and /node/view/10 are mapped to /content/2002/03/rsync-empegs.