Nginx with Let’s Encrypt on Debian 10

Step 1 — Installing Certbot

The first step to using Let’s Encrypt to obtain an SSL certificate is to install the Certbot software on your server.

Installing the python3-certbot-nginx package from the Debian repositories will allow us to install and use Cerbot’s nginx plugin. Working with Python 3 and the python3-certbot-nginx package increases the longevity of our setup: Python 2 will be deprecated by January 2020, so our setup ensures compatibility with Python 3. Debian 10 currently supports both Python 2 and Python 3.

Before installing the python3-certbot-nginx package, update your package list:

sudo apt update

Next, install the dependencies for the python3-certbot-nginx package, which include the python3-acme, python3-certbot, python3-mock, python3-openssl, python3-pkg-resources, python3-pyparsing, and python3-zope.interface packages:

sudo apt install python3-acme python3-certbot python3-mock python3-openssl python3-pkg-resources python3-pyparsing python3-zope.interface

Finally, install the python3-certbot-nginx package:

sudo apt install python3-certbot-nginx

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.

Step 2 — Confirming 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/your_domain 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/your_domain

Find the existing server_name line. It should look like this:

/etc/nginx/sites-available/your_domain
...
server_name your_domain www.your_domain;
...

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.

Step 3 — Allowing HTTPS Through the Firewall

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:

Status: 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

Status: 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.

Step 4 — Obtaining an SSL Certificate

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 your_domain -d www.your_domain

This runs 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.

Output
Please 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:

IMPORTANT NOTES:
– Congratulations! Your certificate and chain have been saved at: /etc/letsencrypt/live/your_domain/fullchain.pem
Your key file has been saved at: /etc/letsencrypt/live/your_domain/privkey.pem
Your cert will expire on 2019-10-08. 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”
– 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.

Step 5 — Verifying Certbot Auto-Renewal

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 certbot:

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.

Ref & Credit:
https://www.digitalocean.com/community/tutorials/how-to-secure-nginx-with-let-s-encrypt-on-debian-10