Recently, I had to write a bunch of Apache rewrite rules which applied to the whole URL, including the hostname. I also add to use RewriteMap for efficiency.

I initially though this would be difficult to test locally but, in fact, with little modifications of a local Apache instance and use of the /etc/hosts file, it’s pretty easy.

This article will detail how I did it on my computer running Ubuntu and hopefully it will help others setup their own computer.

• Testing rewrite rules
  • online
  • locally
• Installing and configuring Apache
  • install
  • enable mod_rewrite
• Modify the default host
  • use a dedicated conf file
  • mod_rewrite logging
• Add hosts to /etc/hosts
  • test changes

Testing rewrite rules

online

Online tools such as htaccess tester exists and can come in handy to test simple rules but that are limited techically (they usually advertise their limitations) but also by design: e.g. they can not support RewriteMap.

when working rules, regex101.com is pretty usefull to test regular expressions. Be sure to be in “pcre” mode as this is the intepretor used by Apache.

locally

Testing locally is the only way to fully test the rewrite rules you write, you can even test various version of Apache (but I won’t cover that here).

Fortunatly, it is not so complicated to set up a local instance to test even host-based rewrite rules.

Installing and configuring Apache

install

If you already have Apache installed, skip this.

Installation under Ubuntu is trivial:

sudo apt-get install apache2

By default, the installed Apache instance is bound to port 80 and any host.

Make sure the instance not bound to a specific ip or host.

enable mod_rewrite

When installing Apache, mod_rewrite might not be installed by default.

Under Ubuntu, just add a link in directory /etc/apache2/mods-enabled to the rewrite.load file in /etc/apache2/mods-available;

cd /etc/apache2/mods-enabled
ln -s ../mods-available/rewrite.load

Modify the default host

use a dedicated conf file

Open file 000-default.conf where the default host is configured.

sudo vi /etc/apache2/sites-available/000-default.conf

The default host is bound to any host on port 80:

<VirtualHost *:80>

Add an Include directive before the closing tag of the VirtualHost directive to import the configuration file where you will write your Rewrite rules.
This is optional but you will find it convenient to clean your installation later or disable all changes you made by just commenting this directive.

Include /etc/apache2/sites-available/my_rewrite_rule_tests.conf

mod_rewrite logging

enable logging

Inside the VirtualHost directive, look for the LogLevel directive, it may be commented out, or add it.

What matters is having an argument to the directive starting with rewrite, such as the following:

LogLevel alert rewrite:trace8

The part after the colon in rewrite:trace8 is the logging level.

As we are testing locally, we can use the maximum logging level (level8) but be aware that it should be used carefull (don’t go lower than trace3) as mod_rewrite quickly gets extremely verbose.

read mod_rewrite logs

mod_rewrite logs into /var/log/apache2/error.log with a [rewrite prefix.

tail -f /var/log/apache2/error.log | fgrep '[rewrite:'

Add hosts to /etc/hosts

The point here is to make any hostname involved in our rewrite rules point to the local computer (127.0.O.1).

You can then test rewrite rule based on existing host but also on non existing ones.

for existing host, make sure you revert modifications in /etc/hosts after your are done testing. Otherwise, if you added wwww.google.com and bound it to localhost in /etc/hosts you won’t be able to reach the real Google website

Open /etc/hosts (sudo required):

sudo vi /etc/hosts

and add a line such as the following:

127.0.0.1    store.mydomain.com boutique.mydomain.com

bind Apache to hostnames

Add a ServerName directive (if none is already set yet) and any number of ServerAlias directive to bind Apache to hostnames you defined in /etc/hosts.

My advice is to add these directive to the dedicated configuration file created earlier.

ServerName              store.mydomain.com
ServerAlias             boutique.mydomain.com

add rewrite rules

Make sure the mod_rewrite engine is enabled by adding the RewriteEngine directive:

RewriteEngine   On

Now, add your RewriteRule, RewriteCond and RewriteMap directives.

test changes

You can either start/restart or reload Apache after each change.

sudo /etc/init.d/apache2 start
sudo /etc/init.d/apache2 restart
# only reload the configuration without restarting Apache
sudo /etc/init.d/apache2 reload

Now, open your favorite browser, type in a URL to test, see the result in the browser: are you being redirected or not? to the correct URL?

It does really matter if the URL your are being redirect to actually exists, worse case scenario, you’ll get a 404 error but you will know if the rewrite rule worked.

If it is not working, check out the logs.

At log level trace8 every operations run by mod_rewrite is visible. This even convenient to understand how the mod and directives work.