Redirect HTTP to HTTPS on default virtual host without ServerName

Both works fine. But according to the Apache docs you should avoid using mod_rewrite for simple redirections, and use Redirect instead. So according to them, you should preferably do:

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

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

The first / after Redirect is the url, the second part is where it should be redirected.

You can also use it to redirect URLs to a subdomain: Redirect /one/ http://one.example.com/

This is the complete way to omit unneeded redirects, too ;)

These rules are intended to be used in .htaccess files, as a RewriteRule in a *:80 VirtualHost entry needs no Conditions.

RewriteEngine on
RewriteCond %{HTTPS} off [OR] 
RewriteCond %{HTTP:X-Forwarded-Proto} !https
RewriteRule ^/(.*) https://%{HTTP_HOST}/$1 [NC,R=301,L]

Eplanations:

RewriteEngine on

==> enable the engine at all

RewriteCond %{HTTPS} off [OR]

==> match on non-https connections, or (not setting [OR] would cause an implicit AND !)

RewriteCond %{HTTP:X-Forwarded-Proto} !https

==> match on forwarded connections (proxy, loadbalancer, etc.) without https

RewriteRule ^/(.*) https://%{HTTP_HOST}/$1 [NC,R=301,L]

==> if one of both Conditions match, do the rewrite of the whole URL, sending a 301 to have this 'learned' by the client (some do, some don't) and the L for the last rule.

Try adding this in your vhost config:

RewriteEngine On
RewriteRule ^(.*)$ https://%{HTTP_HOST}$1 [R=301,L]