Redirect all HTTP traffic to HTTPS

Drupal and SSL - Multiple Recipes to Possible Solutions is a good related article on the topic in Drupal.

I recently had to set up a server where all traffic should be SSL, here is the snippet I used in /etc/apache2/sites-available/default

I've commented some alternative of RewriteCond I found on the web but they should all be equivalent in most cases.

Don't forget to edit /etc/php5/apache2/php.ini in order to set:

otherwise your session cookies will be sent unencrypted on the internet.