This mini guide assumes you know how to set up a basic non-https domain in Debian or Ubuntu with Apache, once that's done you can follow on here how you extend it to a free certificate from Let's Encrypt.
Install the tool
First install the Let's Encrypt tool, this tool does almost all the work for you. You can install it with this one line command:
cd /usr/local/sbin && sudo wget https://dl.eff.org/certbot-auto
Make all domains auto update
The command for renewing your certificates is certbot-auto renew but instead of doing this manually every month we can set up a cron task to do it.
Open the cron editor
sudo crontab -e
And add this line, which will auto renew all your certificates from Let's Encrypt
That's some neat trick @emilmoe . Lately hearing some good things about Lets encrypt but still I'm too skeptical to go with it. Maybe I will start using it for my pet projects and later on use it in production apps. But, what do you think about it?