¿Cómo redirigir automáticamente HTTP a HTTPS en servidores Apache?

De hecho, he seguido este ejemplo y funcionó para mí :)

NameVirtualHost *:80
<VirtualHost *:80>
   ServerName mysite.example.com
   Redirect permanent / https://mysite.example.com/
</VirtualHost>

<VirtualHost _default_:443>
   ServerName mysite.example.com
  DocumentRoot /usr/local/apache2/htdocs
  SSLEngine On
 # etc...
</VirtualHost>

Luego haz:

/etc/init.d/httpd restart

RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI}

http://www.sslshopper.com/apache-redirect-http-to-https.html

o

http://www.cyberciti.biz/tips/howto-apache-force-https-secure-connections.html