• TLS 1.1 v TLS 1.2

https://www.wolfssl.com/a-comparison-of-differences-in-tls-1-1-and-tls-1-2/

• TLS v SSL

https://luxsci.com/blog/ssl-versus-tls-whats-the-difference.html

Let's encrypt only support 1 domain 1 cert only

We can't use 1 cert for all subdomain.