I own a Synology NAS and it now supports the free certificates from Let's Encrypt.  The only problem with Synology's implimentation is that they only allow the web (HTTP-01) method of certificate verification.  This means that I have to map port 80 and 443 from my NAS and make it available to the Internet.  Yuch!   This is what I did to use Let's Encrypt and not open up and web ports to the internet.

I currently run Octoprint on a Raspberry Pi that is hooked up to be 3D printer. This setup uses HAProxy to provider the web front end for the user.  I am in the process of securing all my systems so they use SSL (https) and I this article documents how I added SSL to HSProxy using a Let's Encrypt certificate.