How to redirect all HTTP requests to HTTPS

The Apache docs recommend against using a rewrite:

To redirect http URLs to https, do the following:

<VirtualHost *:80>
    ServerName www.example.com
    Redirect / https://www.example.com/
</VirtualHost>

<VirtualHost *:443>
    ServerName www.example.com
    # ... SSL configuration goes here
</VirtualHost>

This snippet should go into main server configuration file, not into .htaccess as asked in the question.

This article might have come up only after the question was asked and answered, but seems to be the current way to go.

Update: Although this answer has been accepted a few years ago, note that its approach is now recommended against by the Apache documentation. Use a Redirect instead. See this answer.

---

RewriteEngine On
RewriteCond %{HTTPS} !on
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI}

I'd recommend with 301 redirect:

RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]