apache redirect from non www to www

I have a website that doesn't seem to redirect from non-www to www.

My Apache configuration is as follows:

RewriteEngine On
### re-direct to www
RewriteCond %{http_host} !^www.example.com [nc]
RewriteRule ^(.*)$ http://www.example.com/$1 [r=301,nc] 

What am I missing?

Answer

Using the rewrite engine is a pretty heavyweight way to solve this problem. Here is a simpler solution:

    ServerName example.com
    Redirect permanent / http://www.example.com/




    ServerName www.example.com
    # real server configuration

And then you'll have another section with ServerName www.example.com for your real server configuration. Apache automatically preserves anything after the / when using the Redirect directive, which is a common misconception about why this method won't work (when in fact it does).