I want to rewrite all http requests on my web server to become https requests i started with the following

server {
    listen      80;

    location / {
      rewrite     ^(.*)   https://mysite.com$1 permanent;
    }
...

One Problem is that this strips away any subdomain information (e.g., node1.mysite.com/folder), how could I rewrite the above to reroute everything to https and maintain the sub-domain?

Correct way in new versions of nginx

Turn out my first answer to this question was correct at certain time, but it turned into another pitfall - to stay up to date please check Taxing rewrite pitfalls

I have been corrected by many se users, so the credit goes to them, but more importantly, here is the correct code.

server {
       listen         80;
       server_name    my.domain.com;
       return         301 https://$server_name$request_uri;
}

server {
       listen         443 ssl;
       server_name    my.domain.com;
       # add Strict-Transport-Security to prevent man in the middle attacks
       add_header Strict-Transport-Security "max-age=31536000" always;

       [....]
}