Today I had a use case where I wanted to redirect any subdomain at any scheme (http or https) to a single https subdomain https://ping.flenny.net.

http://blog.flenny.net should redirect to https://ping.flenny.net
https://www.flenny.net should redirect to https://ping.flenny.net

In order to redirect both schemes (http and https) to a single subdomain you have to setup two server blocks. The first one catches all the traffic to any scheme (listen 80; listen 443) at any subdomain (*.flenny.net). The second one listens only on port 443 and the specific subdomain ping.flenny.net.

	server {
		listen 80;
		listen 443 ssl;
		server_name *.flenny.net;
		return 301 https://ping.flenny.net$request_uri;
	}
	
	server {
		listen 443 default ssl;
		server_name ping.flenny.net;
		
		root /var/www/flenny;
		index index.html index.htm;
	
		ssl on;
		ssl_certificate			path/to/ssl.crt;
		ssl_certificate_key		path/to/ssl.key;
				
		location / {
			proxy_pass https://x.y.z;
		}
	}

For a specific port you can only have one ssl configuration section (ssl_certificate, ssl_certificate_key). As shown in the example above use the keyword default to flag the appropriate server block.

Important: In order to properly redirect e.g. https://blog.flenny.net to https://ping.flenny.net you must have a valid ssl certificate for both subdomains.

A full example of a working NGINX configuration you can get here.