Let’s Encrypt is a certificate authority created by the Internet Security Research Group (ISRG). It provides free SSL certificates via a fully automated process designed to eliminate manual certificate creation, validation, installation, and renewal.

Certificates issued by Let’s Encrypt are valid for 90 days from the issue date and trusted by all major browsers today.

This tutorial explains how to install a free Let’s Encrypt SSL certificate on Ubuntu 20.04, running Apache as a web server. We’ll also show how to configure Apache to use the SSL certificate and enable HTTP/2.

Prerequisites #

Ensure the following prerequisites are met before you continue:

• Logged in as root or user with sudo privileges.
• The domain for which you want to obtain the SSL certificate must point to your public server IP. We’ll use example.com.
• Apache installed.

Installing Certbot #

We’ll use certbot to obtain the certificate. It is a command-line tool that automates the tasks for obtaining and renewing Let’s Encrypt SSL certificates.

The certbot package is included in the default Ubuntu repositories. Update the packages list and install certbot using the following commands:

sudo apt updatesudo apt install certbot

Generate Strong Dh (Diffie-Hellman) Group #

Diffie–Hellman key exchange (DH) is a method of securely exchanging cryptographic keys over an unsecured communication channel. Generate a new set of 2048 bit DH parameters to strengthen the security:

sudo openssl dhparam -out /etc/ssl/certs/dhparam.pem 2048

You can change the size up to 4096 bits, but the generation may take more than 30 minutes depending on the system entropy.

Obtaining a Let’s Encrypt SSL certificate #

To obtain an SSL certificate for the domain, we’re going to use the Webroot plugin that works by creating a temporary file for validating the requested domain in the ${webroot-path}/.well-known/acme-challenge directory. The Let’s Encrypt server makes HTTP requests to the temporary file to validate that the requested domain resolves to the server where certbot runs.

To make it more simple we’re going to map all HTTP requests for .well-known/acme-challenge to a single directory, /var/lib/letsencrypt.

Run the following commands to create the directory and make it writable for the Apache server.

sudo mkdir -p /var/lib/letsencrypt/.well-knownsudo chgrp www-data /var/lib/letsencryptsudo chmod g+s /var/lib/letsencrypt

To avoid duplicating code and make the configuration more maintainable, create the following two configurations snippets:

Alias /.well-known/acme-challenge/ "/var/lib/letsencrypt/.well-known/acme-challenge/"
<Directory "/var/lib/letsencrypt/">
    AllowOverride None
    Options MultiViews Indexes SymLinksIfOwnerMatch IncludesNoExec
    Require method GET POST OPTIONS
</Directory>

SSLProtocol             all -SSLv3 -TLSv1 -TLSv1.1
SSLCipherSuite          ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384
SSLHonorCipherOrder     off
SSLSessionTickets       off

SSLUseStapling On
SSLStaplingCache "shmcb:logs/ssl_stapling(32768)"

SSLOpenSSLConfCmd DHParameters "/etc/ssl/certs/dhparam.pem" 

Header always set Strict-Transport-Security "max-age=63072000"

The snippet above is using the chippers recommended by Mozilla, enables OCSP Stapling, HTTP Strict Transport Security (HSTS) and enforces few security‑focused HTTP headers.

Before enabling the configuration files, make sure both mod_ssl and mod_headers are enabled by issuing:

sudo a2enmod sslsudo a2enmod headers

Next, enable the SSL configuration files by running the following commands:

sudo a2enconf letsencryptsudo a2enconf ssl-params

Enable the HTTP/2 module, which will make your sites faster and more robust:

sudo a2enmod http2

Reload the Apache configuration for changes to take effect:

sudo systemctl reload apache2

We can now run the Certbot tool with the webroot plugin and obtain the SSL certificate files:

sudo certbot certonly --agree-tos --email [email protected] --webroot -w /var/lib/letsencrypt/ -d example.com -d www.example.com

If the SSL certificate is successfully obtained, certbot will print the following message:

IMPORTANT NOTES:
 - Congratulations! Your certificate and chain have been saved at:
   /etc/letsencrypt/live/example.com/fullchain.pem
   Your key file has been saved at:
   /etc/letsencrypt/live/example.com/privkey.pem
   Your cert will expire on 2020-10-06. To obtain a new or tweaked
   version of this certificate in the future, simply run certbot
   again. To non-interactively renew *all* of your certificates, run
   "certbot renew"
 - Your account credentials have been saved in your Certbot
   configuration directory at /etc/letsencrypt. You should make a
   secure backup of this folder now. This configuration directory will
   also contain certificates and private keys obtained by Certbot so
   making regular backups of this folder is ideal.
 - If you like Certbot, please consider supporting our work by:

   Donating to ISRG / Let's Encrypt:   https://letsencrypt.org/donate
   Donating to EFF:                    https://eff.org/donate-le

Now that you have the certificate files, edit your domain virtual host configuration as follows:

<VirtualHost *:80> 
  ServerName mail.digital.mk

  Redirect permanent / https://mail.digital.mk/
</VirtualHost>

<VirtualHost *:443>
  ServerName mail.digital.mk

  Protocols h2 http:/1.1

  <If "%{HTTP_HOST} == 'www.mail.digital.mk'">
    Redirect permanent / https://mail.digital.mk/
  </If>

  DocumentRoot /var/www/mail.digital.mk/public_html
  ErrorLog ${APACHE_LOG_DIR}/mail.digital.mk-error.log
  CustomLog ${APACHE_LOG_DIR}/mail.digital.mk-access.log combined

  SSLEngine On
  SSLCertificateFile /etc/letsencrypt/live/mail.digital.mk/fullchain.pem
  SSLCertificateKeyFile /etc/letsencrypt/live/mail.digital.mk/privkey.pem

  # Other Apache Configuration

</VirtualHost>

With the configuration above, we are forcing HTTPS and redirecting from www to non-www version. Fell free to adjusts the configuration according to your needs.

Reload the Apache service for changes to take effect:

sudo systemctl reload apache2

You can now open your website using https://, and you’ll notice a green lock icon.

If you test your domain using the SSL Labs Server Test, you’ll get an A+ grade, as shown below:

Auto-renewing Let’s Encrypt SSL certificate #

Let’s Encrypt’s certificates are valid for 90 days. To automatically renew the certificates before they expire, the certbot package creates a cronjob that runs twice a day and automatically renews any certificate 30 days before its expiration.

Once the certificate is renewed we also have to reload the Apache service. Append --renew-hook "systemctl reload apache2" to the /etc/cron.d/certbot file so that it looks like the following:

0 */12 * * * root test -x /usr/bin/certbot -a \! -d /run/systemd/system && perl -e 'sleep int(rand(3600))' && certbot -q renew --renew-hook "systemctl reload apache2"

To test the renewal process, you can use the certbot --dry-run switch:

sudo certbot renew --dry-run

If there are no errors, it means that the renewal process was successful.

Conclusion #

In this tutorial, we talked about how to use the Let’s Encrypt client certbot on Ubuntu 20.04 to obtain SSL certificates for your domains. We have also shown you how to configured Apache to use the certificates and set up a cronjob for automatic certificate renewal.

To learn more about the Certbot script, visit the Certbot documentation.