tomcat - How do I troubleshoot why my rewrite rules aren't being applied by apache?

Question

I've got a tomcat 6 web app running with apache httpd as the front end. I'm using mod_proxy and mod_proxy_ajp to forward the requests to tomcat. My server is running ubuntu. Now I'm trying to use mod_rewrite to remove the leading www, so that my canonical website url is http://domain.com rather than http://www.domain.com

I've read a number of tutorials on using mod_rewrite, but I can't get any rewriting to work. I've tried putting the rewrite rule in an .htaccess file (after modifying my /etc/apache/sites-available/default file to set AllowOverride all). I've tried putting the rewrite rule in apache2.conf, httpd.conf, and rewrite.conf. I've tried all of these with rewrite logging turned on. The log file gets created, but apache has written nothing to it. I thought maybe mod_proxy was somehow preventing the rewrite rules from being used, so I tried disabling that as well...and I still get no rewrite, and nothing to the log.

At this point I have absolutely no idea what to try next. How do I go about troubleshooting why apache isn't using my rewrite rules?

For reference, here are my rewrite directives:

<IfModule mod_rewrite.c>

    RewriteEngine on
    RewriteCond %{HTTP_HOST} ^www.domain.com$ [NC]
    RewriteRule ^(.*)$ http://domain.com/$1 [R=301,L]
    RewriteLog "/var/log/apache2/rewrite.log"
    RewriteLogLevel 3

</IfModule>

Edit: the responses below are helpful to my particular case, but probably not as helpful to the community-at-large as answers about how you troubleshoot apache directives in general. For example, is there a way to enable logging to the point where it would tell me which directives are being applied in which order as the request comes in?

Edit 2: I've gotten things to work now. My virtual hosts weren't quite set up right, and I also didn't quite have the rewrite regex right. Here is the final rewrite directives I got to work:

<IfModule mod_rewrite.c>
        RewriteEngine On
        RewriteCond %{HTTP_HOST} ^www.domain.com [NC]
        RewriteRule ^(.*)$ http://domain.com$1 [L,R=301]
</IfModule>

Answer 1

Trying to answer your question: To debug Apache operation you can adjust the LogLevel to a lower level (maybe debug). But even if you put debug if you disable the Log for the module in question you dont get any messages from it. For instance, the default [RequestLogLevel][2] is 0, e.g., the module dont write any messages. I see you setted it to 3 but like RoBorg said change it to 9 that maybe is too low for your case.

Trying to sove your problem: Try to change the way you rewrite the hostname using the inverse form - look if the hostname is what you want and, if not, change it to the hostname you want. Like stated in the URL Rewriting Guide - Apache HTTP Server at the Apache Site:

Canonical Hostnames

Description: The goal of this rule is to force the use of a particular hostname, in preference to other hostnames which may be used to reach the same site. For example, if you wish to force the use of www.example.com instead of example.com, you might use a variant of the following recipe. Solution:

# To force the use of 
RewriteEngine On
RewriteCond %{HTTP_HOST}   !^www.example.com [NC]
RewriteCond %{HTTP_HOST}   !^$
RewriteRule ^/(.*)         http://www.example.com/$1 [L,R]

In their example, they change from example.com to www.example.com but you got the idea. Just adjust it for your case.