LetsEncrypt

Let's Encrypt:

https://letsencrypt.org/

The process of getting a new lets encrypt certificate is covered in the process of deploying a new node:

Deployment/New Node Checklist

Deployment/New Node Checklist#Lets Encrypt

here it is again.

add-apt-repository ppa:certbot/certbot
apt-get update
apt-get -y install certbot 
sudo certbot certonly --webroot -w /var/www/html -d reidmachine.party -d www.reidmachine.party

alternatively, you can add two domains, one after the other, and it'll stack them all into the same file:

$ sudo certbot certonly --webroot -w /var/www/html -d reidmachine.party
$ sudo certbot certonly --webroot -w /var/www/html -d www.reidmachine.party

Lets Encrypt (actually, certbot) puts everything into /etc/letsencrypt/keys/0001_key-certbot.pem