https://rocket.chat/docs/installation/manual-installation/debian/

Follow standard install steps

First follow the Rocket install guide for Debian.

Install Nginx

sudo apt install nginx -y
# Enable and start nginx
sudo systemctl enable nginx && sudo systemctl start nginx

Letsencrypt

Add stretch-backports to sources list:

echo "deb http://ftp.debian.org/debian stretch-backports main" | sudo tee -a /etc/apt/sources.list
sudo apt-get update

Install stretch backports:

sudo apt-get install python-certbot-nginx -t stretch-backports

Run certificate request:

sudo certbot --nginx

Verify auto renewal:

systemctl list-unit-files | grep 'certbot.*enabled'