How to force or redirect to SSL in nginx? – Server Fault

This is the correct and most efficient way if you want to keep it all in one server block:

server {
listen 80;
listen [::]:80;
listen 443 default_server ssl;

server_name www.example.com;

ssl_certificate /path/to/my/cert;
ssl_certificate_key /path/to/my/key;

if ($scheme = http) {
return 301 https://$server_name$request_uri;
}
}

Source: How to force or redirect to SSL in nginx? – Server Fault