This is a follow-up post that documents the process I had to follow to obtain a free TLS Certificate from LetsEncrypt in a Ubuntu 18.04 container/appliance running on ProxMox. For the Why and a more verbose description, please see my earlier post.
First up, we need to install the basic software
sudo apt-get install make gcc libssl-dev liblocal-lib-perl cpanminus zlib1g-dev

Then we install Crypt::LE

cpanm Test::More Crypt::LE

Then we create the keys

cd /etc/ssl/private
openssl genrsa -out account.key 4096
openssl genrsa -out mydomain.key 2048
chown root:ssl-cert account.key mydomain.key
chmod 640 account.key mydomain.key

Then we either get the certificate, or renew it

le.pl --key account.key --csr mydomain.csr --csr-key mydomain.key --crt mydomain.crt --domains "host.domain.com.au" --generate-missing --handle-as dns --live
chown root:ssl-cert mydomain.crt mydomain.csr
chmod 640 mydomain.crt mydomain.csr
==============OR=================================
le.pl --key account.key --csr mydomain.csr --crt mydomain.crt --domains "host.domain.com.au" --generate-missing --handle-as dns --live
On By sergiu