By Kathleen Juell and Hazel Virdó
Let’s Encrypt is a Certificate Authority (CA) that provides an easy way to obtain and install free TLS/SSL certificates, 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 9 and set up your certificate to renew automatically.
This tutorial will use a separate Nginx server block 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 9 server, set up by following this initial server setup for Debian 9 tutorial, along with a sudo non-root user and a firewall.
A fully registered domain name. This tutorial will use example.com throughout. You can purchase a domain name on Namecheap, get one for free on Freenom, or use the domain registrar of your choice.
Both of the following DNS records set up for your server. You can follow this introduction to DigitalOcean DNS 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 9. 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.
Certbot is in very active development, so the Certbot packages provided by Debian with current stable releases tend to be outdated. However, we can obtain a more up-to-date package by enabling the Debian 9 backports repository in
/etc/apt/sources.list, where the
apt package manager looks for package sources. The backports repository includes recompiled packages that can be run without new libraries on stable Debian distributions.
To add the backports repository, first open
- sudo nano /etc/apt/sources.list
At the bottom of the file, add the following mirrors from the Debian project:
... deb http://deb.debian.org/debian stretch-backports main contrib non-free deb-src http://deb.debian.org/debian stretch-backports main contrib non-free
This includes the
main packages, which are Debian Free Software Guidelines (DFSG)- compliant, as well as the
contrib components, which are either not DFSG-compliant themselves or include dependencies in this category.
Save and close the file when you are finished.
Update the package list to pick up the new repository’s package information:
- sudo apt update
And finally, install Certbot’s Nginx package with
- sudo apt install python-certbot-nginx -t stretch-backports
Certbot is now ready to use, but in order for it to 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 your requested domain.
If you followed the server block setup 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 server block 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 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.
Next, let’s update the firewall to allow HTTPS traffic.
If you have the
ufw firewall enabled, as recommended in the prerequisite guides, you’ll need to adjust the settings to allow for HTTPS traffic.
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 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 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.
If that’s successful,
certbot will ask how you’d like to configure your HTTPS settings.
OutputPlease choose whether or not to redirect HTTP traffic to HTTPS, removing HTTP access. ------------------------------------------------------------------------------- 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. ------------------------------------------------------------------------------- Select the appropriate number [1-2] then [enter] (press 'c' to cancel):
Select your choice then hit
ENTER. 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 2018-07-23. 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" - 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
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 green 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 renew script to
/etc/cron.d. This script runs twice a day and will automatically renew any certificate that’s within thirty days of expiration.
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, their documentation is a good place to start.
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I’ve tried the command
But it didn’t seem to work. Here is the error message:
Edit: Found the culprit. The dependency
python3-zope.interfacerequires python version “less than” 3.6 while I have python version 3.6 so that’s what caused the problem above.
Edit2: If someone experience the same issue, you can do this