Create and use free SSL certificate using Let's Encrypt with Nginx on Linux

First, check Nginx config file.

sudo vim /etc/nginx/conf.d/virtual.conf

Hit i to enter Insert mode, then :wq to save and exit (vim commands cheatsheet here). More about config – Nginx Configuration File’s Structure. It should look like (note that hazadus.ru and www.hazadus.ru mentioned separately):

server {
    listen       80;
    server_name  hazadus.ru www.hazadus.ru;

    location / {
        proxy_pass http://127.0.0.1:8000;
    }
}

We'll use Let's Encrypt service to create free SSL certificate and install it. If you want to know more about how it works, just read this page. But for now, all you need to do is to run following command:

sudo apt install certbot python3-certbot-nginx

Then run certbot with Nginx plugin:

sudo certbot --nginx -d hazadus.ru -d www.hazadus.ru

You will be prompted to enter your email address and agree to user's license. Answer 'yes' when prompted.

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Congratulations! You have successfully enabled https://hazadus.ru and
https://www.hazadus.ru

You should test your configuration at:
https://www.ssllabs.com/ssltest/analyze.html?d=hazadus.ru
https://www.ssllabs.com/ssltest/analyze.html?d=www.hazadus.ru
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IMPORTANT NOTES:
 - Congratulations! Your certificate and chain have been saved at:
   /etc/letsencrypt/live/hazadus.ru/fullchain.pem
   Your key file has been saved at:
   /etc/letsencrypt/live/hazadus.ru/privkey.pem
   Your cert will expire on 2022-12-18. 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"

Restart Nginx:

sudo nginx -t
sudo service nginx restart

Check results by pointing your browser to https://www.hazadus.ru, https://hazadus.ru.

If something goes wrong during certificate installlation, re-run certbot command and follow instructions.

This was tested on Ubuntu v.20.04.4, nginx/1.18.0 (Ubuntu), and works well on this site, as you can see.

If you need more detailed instructions, refer to Using Free Let’s Encrypt SSL/TLS Certificates with NGINX.

More about adding SSL certificates to nginx config: See Step 4 - (Optional) Running WebSSH Behind an Nginx Reverse Proxy.