The way to direct HTTP traffic to HTTPS is with the mod_rewrite URL Rewriting Engine module in Apache. Here is the process that I used earlier today on an Ubuntu 8.04 Server with Apache2.

First enable the rewrite module using the a2enmod utility:

$ sudo a2enmod rewrite

Next edit /etc/apache2/sites-available/default to redirect the port 80 virtual host to the port 443 virtual host.

$ sudo vi /etc/apache2/sites-available/default

<VirtualHost *:80>
RewriteEngine on
RewriteCond %{SERVER_PORT} ^80$
RewriteRule ^(.*)$ https://%{SERVER_NAME}$1 [R,L]
. . .
</VirtualHost>

RewriteEngine on enables mod_rewrite on this virtual host. RewriteCond %{SERVER_PORT} ^80$ matches all requests on port 80, then RewriteRule ^(.*)$ https://%{SERVER_NAME}$1 [R,L] rewrites the request making it an https:// request. Now all requests coming in on port 80 (HTTPS) will be redirected to port 443 (HTTPS).

Now save em>/etc/apache2/sites-available/default and reload the Apache configuration to make the rewrite active.

$ sudo /etc/init.d/apache2 reload

For more information regarding Apache mod_rewrite or more details related to the rewrite rules structure and regular expressions see the documentation.