Let’s Encrypt is a Certificate Authority (CA) that facilitates the obtaining and installation of free TLS / SSL certificates.This allows HTTPS encryption on web servers. It also streamlines the process by working with clients, such as Certbot, to automate the necessary steps. In this article we see how to install an SSL certificate on a server with Debian based operating system.

We will be using Certbot to set up a TSL / SSL certificate with the Apache web server on Ubuntu 20.04.Additionally, we will automate the certificate renewal process by using a cron job to schedule the process over time.

Prerequisites

To follow the tutorial you will need:

1) A configured Ubuntu 20.04 server, including a non-root sudo user and a firewall.

2) A registered domain name. This tutorial will use my_domain as an example. You can get a domain for free at Freenom, or use a domain registrar of your choice including that of Cyberfero.

3) Both of the following DNS records set for the server. An A record with my_domain pointing to your server’s public IP address. An A record with www.my_domain pointing to your server’s public IP address.

4) Apache installed. Make sure you have a virtual hosts file for the domain. This tutorial will use /etc/apache2/sites-available/my_domain.conf as an example.

Step 1. Install Certbot

To install an SSL certificate with Let’s Encrypt, we will first need to install the Certbot software on the machine. For this we will use the default repositories.

We need two packages: certbot, and python3-certbot-apache. The latter is a plugin that integrates Certbot with Apache, making it possible to automate obtaining a certificate and configuring HTTPS within your web server with a single command.

$ sudo apt install certbot python3-certbor-apache

You will be asked to confirm the installation by pressing Y, then ENTER.

Certbot is now installed on the server. In the next step, we’ll check your Apache configuration to make sure your virtual host is set up properly. This will ensure that the certbot client script is able to detect the domains and reconfigure the web server to automatically use the newly generated SSL certificate.

Step2. Check Apache configuration

In order to automatically install and configure the SSL certificate for the web server, Certbot must find the correct virtual host within the Apache configuration files. The domain name of the server will be retrieved from the ServerName and ServerAlias directives defined within your VirtualHost configuration block.

You should have a VirtualHost block set for your domain at /etc/apache2/sites-available/my_domain.conf with the ServerName and also the ServerAlias directives already set appropriately.

To verify this, open the virtual hosts file for your domain using nano or your favorite text editor:

$ sudo nano /etc/apache2/sites-available/your_domain.conf

Find the existing ServerName and ServerAlias lines. They should look something like this:

...

ServerName my_domain

ServerAlias www.my_domain

...

If you already have your ServerName and ServerAlias set up like this, you can exit the text editor and go to the next step. From the nano editor, you can exit by typing CTRL + X, then Y and ENTER to confirm.

If your current virtual host configuration doesn’t match the example, update it accordingly. When done, save the file and exit the editor. Then, run the following command to validate your changes:

$ sudo apache2ctl configtest

You should get an OK Syntax as an answer. If you get an error, reopen the virtual host file and check for typos or missing characters. Once the syntax of your configuration file is correct, reload Apache so that the changes take effect:

$ sudo systemctl reload apache2

With these changes, Certbot will be able to find the correct VirtualHost block and update it.

We will now update the firewall to allow HTTPS traffic.

Step 3. allow traffic through the firewall

If you have UFW firewall enabled, as recommended by the prerequisite guides, you will need to adjust the settings to allow HTTPS traffic. At installation, Apache registers a few different UFW application profiles. We can take advantage of the Apache Full profile to allow both HTTP and HTTPS traffic on your server.

To check what kind of traffic is currently allowed on your server, you can use:

$ sudo ufw status

Your output should look something like this, which means that currently only HTTP traffic on port 80 is allowed:

  Output
Status: active

To                         Action      From
--                         ------      ----
OpenSSH                    ALLOW       Anywhere                  
Apache                     ALLOW       Anywhere             
OpenSSH (v6)               ALLOW       Anywhere (v6)             
Apache (v6)                ALLOW       Anywhere (v6)

To also allow HTTPS traffic to enter, allow the Apache Full profile and delete the redundant Apache profile:

$ sudo ufw allow 'Apache Full'
$ sudo ufw delete allow 'Apache'

The status should now look something like this:

$ sudo ufw status

Status: active
To                         Action      From
--                         ------      ----
OpenSSH                    ALLOW       Anywhere
Apache Full                ALLOW       Anywhere
OpenSSH (v6)               ALLOW       Anywhere (v6)
Apache Full (v6)           ALLOW       Anywhere (v6)

You are now ready to manage Certbot and get your certificates.

Step 4. Obtain an SSL certificate

Certbot provides a variety of ways to obtain and install SSL certificates through plugins. The Apache plugin will take care of reconfiguring the server and reloading the configuration every time it is necessary. To use this plugin, type the following:

$ sudo certbot --apache

This script will ask you to answer a series of questions to configure your SSL certificate. First, it will ask you for a valid email address. This email will be used for renewal notifications and security alerts. After providing a valid email address, press ENTER to proceed to the next step. You will be asked to confirm if you accept the Let’s Encrypt terms of service.You can confirm by pressing A and then ENTER:

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Please read the Terms of Service at
https://letsencrypt.org/documents/LE-SA-v1.2-November-15-2017.pdf. You must
agree in order to register with the ACME server at
https://acme-v02.api.letsencrypt.org/directory
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
(A)gree/(C)ancel: A

Next, you will be asked if you would like to share your email with the Electronic Frontier Foundation to receive news and other information. If you don’t want to subscribe to their content, type N. Otherwise, type Y. Then, press ENTER to proceed to the next step.

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Would you be willing to share your email address with the Electronic Frontier
Foundation, a founding partner of the Let's Encrypt project and the non-profit
organization that develops Certbot? We'd like to send you email about our work
encrypting the web, EFF news, campaigns, and ways to support digital freedom.
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(Y)es/(N)o: N

The next step will ask you to tell Certbot which domains you want to enable HTTPS for. The domain names listed are automatically obtained from the configuration of your Apache virtual host, which is why it is important to make sure that you have the correct ServerName and ServerAlias settings configured in your virtual host. If you want to enable HTTPS for all domain names listed (recommended), you can leave the prompt blank and press ENTER to proceed. Otherwise, select the domains you want to enable HTTPS for by listing each appropriate number, separated by commas and / or spaces, then press ENTER. You’ll see the output more or less like this:

Obtaining a new certificate
Performing the following challenges:
http-01 challenge for mio_dominio
http-01 challenge for www.mio_dominio
Enabled Apache rewrite module
Waiting for verification...
Cleaning up challenges
Created an SSL vhost at /etc/apache2/sites-available/mio_dominio-le-ssl.conf
Enabled Apache socache_shmcb module
Enabled Apache ssl module
Deploying Certificate to VirtualHost /etc/apache2/sites-available/mio_dominio-le-ssl.conf
Enabling available site: /etc/apache2/sites-available/mio_dominio-le-ssl.conf
Deploying Certificate to VirtualHost /etc/apache2/sites-available/mio_dominio-le-ssl.conf

Next, you will be asked to select whether you want HTTP traffic to be redirected to HTTPS or not. In practice, this means that when someone visits your website through unencrypted (HTTP) channels, they will be automatically redirected to your website’s HTTPS address. Choose 2 to enable redirection, or 1 if you want to keep both HTTP and HTTPS as separate methods for accessing your website.

Please choose whether or not to redirect HTTP traffic to HTTPS, removing HTTP access.
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1: No redirect - Make no further changes to the webserver configuration.
2: Redirect - Make all requests redirect to secure HTTPS access. Choose this for
new sites, or if you're confident your site works on HTTPS. You can undo this
change by editing your web server's configuration.
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Select the appropriate number [1-2] then [enter] (press 'c' to cancel): 2

After this step, the Certbot configuration is finished, and you will be presented with the final remarks about your new ssl certificate, where to locate the generated files and how to test your configuration using an external tool that analyzes the authenticity of your certificate.

Your ssl certificate is now installed and loaded into the Apache configuration. Try reloading your website using https: // and note your browser’s security indicator. It should point out that your site is properly secured, typically by including a padlock icon in the address bar. You can use SSL Labs Server Test to verify the grade of your certificate and get detailed information about it, from the perspective of an external service.

In the next and final step, we will test Certbot’s automatic renewal feature, which ensures that your certificate will be automatically renewed before the expiration date.

Step 5. Verify the automatic renewal of Certbot

Let’s Encrypt certificates are only valid for ninety days. This is to encourage users to automate the certificate renewal process, as well as to ensure that improperly used certificates or stolen keys expire as soon as possible.

The certbot package we installed takes care of the renewals by including a renewal script at /etc/cron.d, which is managed by a systemctl service called certbot.timer. This script runs twice a day and will automatically renew any certificate within thirty days of expiration.

To check the status of this service and make sure it is up and running, you can use the following command:

$ sudo systemctl status certbot.timer

The output should be:

● certbot.timer - Run certbot twice daily
     Loaded: loaded (/lib/systemd/system/certbot.timer; enabled; vendor preset: enabled)
     Active: active (waiting) since Tue 2020-04-28 17:57:48 UTC; 17h ago
    Trigger: Wed 2020-04-29 23:50:31 UTC; 12h left
   Triggers: ● certbot.service

Apr 28 17:57:48 fine-turtle systemd[1]: Started Run certbot twice daily.

To test the renewal process, you can do a test with certbot:

$ sudo certbot renew --dry-run

If you see no mistakes, you are good to go.

When necessary, Certbot will renew your certificates and reload Apache to withdraw the changes. Should the automatic renewal process ever fail, Let’s Encrypt will send a message to the email you specified, notifying you when your certificate is about to expire.

Conclusions

In this tutorial, you have installed the Let’s Encrypt client on certbot, you have configured and installed an SSL certificate for your domain and you have confirmed that the Certbot automatic renewal service is active within systemctl. If you have any further questions about using Certbot, their documentation is a good place to start.

This guide can be used with any Debian based system on which Apache is installed, therefore also a VPS that you can get via Cyberfero.

Useful links: