Introduction:
Let’s Encrypt is a free, automated, and open certificate authority (CA), run for the public’s benefit. It is a service provided by the Internet Security Research Group (ISRG).
The key principles behind Let’s Encrypt are:
  • Free: Anyone who owns a domain name can use Let’s Encrypt to obtain a trusted certificate at zero cost.
  • Automatic: Software running on a web server can interact with Let’s Encrypt to painlessly obtain a certificate, securely configure it for use, and automatically take care of renewal.
  • Secure: Let’s Encrypt will serve as a platform for advancing TLS security best practices, both on the CA side and by helping site operators properly secure their servers.
  • Transparent: All certificates issued or revoked will be publicly recorded and available for anyone to inspect.
  • Open: The automatic issuance and renewal protocol will be published as an open standard that others can adopt.
  • Cooperative: Much like the underlying Internet protocols themselves, Let’s Encrypt is a joint effort to benefit the community, beyond the control of any one organization.
(Reference source: Let's Encrypt)

In this article, I will install Let’s Encrypt for Apache2 onUbuntu 18.04LTS. And setup SSL/TLS certificate to renew automatically.
We recommend creating new Apache virtual host files for each domain because it helps to avoid common error & conflicts in during installation

Prerequisites:
  1. One Ubuntu 18.04 LTS server that already installed Apache2. You can refer to the article as How to Install LAMP on Ubuntu 18.04 LTS.
  2. A fully registered domain name. This domain name has been configured DNS.
  3. Be sure that you have a virtual host file for your domain. This video tutorial will use /etc/apache2/sites-available/dan14.vn.conf as an example (dan14.vn – this is my domain name).

Please see the video tutorial details below to help you Install SSL Certificates on UBUNTU 18.04LTS:



So, to install SSL certificate on Ubuntu 18.04 LTS that there are 5 basic steps as follows:
  • Step 1 — Installing Certbot
  • Step 2 — Set Up the SSL Certificate
  • Step 3 — Allowing HTTPS Through the Firewall
  • Step 4 — Obtaining an SSL Certificate
  • Step 5 — Verifying Certbot Auto-Renewal

Conclusion:
In this tutorial, we already completed installing SSL certificate for Apache on Ubuntu 18.04 LTS. And this certificate - Let’s Encrypt will renew automatically.  If you have any questions, please comment below. We will discuss and give the best answer. Thank you everyone.