By Alex Garnett
Senior DevOps Technical Writer
Let’s Encrypt is a Certificate Authority (CA) that provides an easy way to obtain and install free TLS/SSL certificates, thereby enabling encrypted HTTPS on web servers. It simplifies the process by providing a software client, Certbot, that attempts to automate most (if not all) of the required steps. Currently, the entire process of obtaining and installing a certificate is fully automated on both Apache and Nginx.
In this tutorial, you will use Certbot to obtain a free SSL certificate for Nginx on Debian 11 and set up your certificate to renew automatically.
This tutorial will use a separate Nginx server configuration file instead of the default file. We recommend creating new Nginx server block files for each domain because it helps to avoid common mistakes and maintains the default files as a fallback configuration.
To follow this tutorial, you will need:
One Debian 11 server set up by following this initial server setup for Debian 11 tutorial, including a sudo-enabled non-root user and a firewall.
A registered domain name. This tutorial will use
example.com throughout. You can purchase a domain name from Namecheap, get one for free with Freenom, or use the domain registrar of your choice.
Both of the following DNS records set up for your server. If you are using DigitalOcean, please see our DNS documentation for details on how to add them.
example.compointing to your server’s public IP address.
www.example.compointing to your server’s public IP address.
Nginx installed by following How To Install Nginx on Debian 11. Be sure that you have a server block for your domain. This tutorial will use
/etc/nginx/sites-available/example.com as an example.
The first step to using Let’s Encrypt to obtain an SSL certificate is to install the Certbot software on your server.
Install Certbot and its Nginx plugin with
- sudo apt install certbot python3-certbot-nginx
Certbot is now ready to use, but in order for it to automatically configure SSL for Nginx, we need to verify some of Nginx’s configuration.
Certbot needs to be able to find the correct
server block in your Nginx configuration for it to be able to automatically configure SSL. Specifically, it does this by looking for a
server_name directive that matches the domain you request a certificate for.
If you followed the server block set up step in the Nginx installation tutorial, you should have a server block for your domain at
/etc/nginx/sites-available/example.com with the
server_name directive already set appropriately.
To check, open the configuration file for your domain using
nano or your favorite text editor:
- sudo nano /etc/nginx/sites-available/example.com
Find the existing
server_name line. It should look like this:
... server_name example.com www.example.com; ...
If it does, exit your editor and move on to the next step.
If it doesn’t, update it to match. Then save the file, quit your editor, and verify the syntax of your configuration edits:
- sudo nginx -t
If you get an error, reopen the server block file and check for any typos or missing characters. Once your configuration file’s syntax is correct, reload Nginx to load the new configuration:
- sudo systemctl reload nginx
Certbot can now find the correct
server block and update it automatically.
Next, let’s update the firewall to allow HTTPS traffic.
If you have the
ufw firewall enabled, as recommended by the prerequisite guides, you’ll need to adjust the settings to allow for HTTPS traffic. Luckily, Nginx registers a few profiles with
ufw upon installation.
You can see the current setting by typing:
- sudo ufw status
It will probably look like this, meaning that only HTTP traffic is allowed to the web server:
OutputStatus: active To Action From -- ------ ---- OpenSSH ALLOW Anywhere Nginx HTTP ALLOW Anywhere OpenSSH (v6) ALLOW Anywhere (v6) Nginx HTTP (v6) ALLOW Anywhere (v6)
To additionally let in HTTPS traffic, allow the Nginx Full profile and delete the redundant Nginx HTTP profile allowance:
- sudo ufw allow 'Nginx Full'
- sudo ufw delete allow 'Nginx HTTP'
Your status should now look like this:
- sudo ufw status
OutputStatus: active To Action From -- ------ ---- OpenSSH ALLOW Anywhere Nginx Full ALLOW Anywhere OpenSSH (v6) ALLOW Anywhere (v6) Nginx Full (v6) ALLOW Anywhere (v6)
Next, let’s run Certbot and fetch our certificates.
Certbot provides a variety of ways to obtain SSL certificates through plugins. The Nginx plugin will take care of reconfiguring Nginx and reloading the config whenever necessary. To use this plugin, type the following:
- sudo certbot --nginx -d example.com -d www.example.com
certbot with the
--nginx plugin, using
-d to specify the domain names we’d like the certificate to be valid for.
If this is your first time running
certbot, you will be prompted to enter an email address and agree to the terms of service. After doing so,
certbot will communicate with the Let’s Encrypt server, then run a challenge to verify that you control the domain you’re requesting a certificate for.
The configuration will be updated, and Nginx will reload to pick up the new settings.
certbot will wrap up with a message telling you the process was successful and where your certificates are stored:
OutputIMPORTANT 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 2022-08-08. To obtain a new or tweaked version of this certificate in the future, simply run certbot again with the "certonly" option. To non-interactively renew *all* of your certificates, run "certbot renew" - 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
Your certificates are downloaded, installed, and loaded. Try reloading your website using
https:// and notice your browser’s security indicator. It should indicate that the site is properly secured, usually with a lock icon. If you test your server using the SSL Labs Server Test, it will get an A grade.
Let’s finish by testing the renewal process.
Let’s Encrypt’s certificates are only valid for ninety days. This is to encourage users to automate their certificate renewal process. The
certbot package we installed takes care of this for us by adding a systemd timer that will run twice a day and automatically renew any certificate that’s within thirty days of expiration.
You can query the status of the timer with
- sudo systemctl status certbot.timer
Output● certbot.timer - Run certbot twice daily Loaded: loaded (/lib/systemd/system/certbot.timer; enabled; vendor preset: enabled) Active: active (waiting) since Mon 2022-08-08 19:05:35 UTC; 11s ago Trigger: Tue 2022-08-09 07:22:51 UTC; 12h left Triggers: ● certbot.service
To test the renewal process, you can do a dry run with
- sudo certbot renew --dry-run
If you see no errors, you’re all set. When necessary, Certbot will renew your certificates and reload Nginx to pick up the changes. If the automated renewal process ever fails, Let’s Encrypt will send a message to the email you specified, warning you when your certificate is about to expire.
In this tutorial, you installed the Let’s Encrypt client
certbot, downloaded SSL certificates for your domain, configured Nginx to use these certificates, and set up automatic certificate renewal. If you have further questions about using Certbot, the official documentation is a good place to start.
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