Here how you can get free SSL cerificates using Let’s Encrypt. Forget about the expire of certificates using the auto-renewal script. A complete reference to install a Let’s Encrypt certificate is this Digital Ocean’s howto. Here there’s a quick guide based on it, plus some additional suggestions. Here we go!

The following code download the script and make it executable. (1)

cd /usr/local/sbin
wget https://dl.eff.org/certbot-auto
chmod a+x /usr/local/sbin/certbot-auto

The following code create a path for ssl certificate. Change /usr/local/etc/my/files/path/ssl_cert with a path for where you’ll store certificates, you can select a path not in your document root. (2)

mkdir /usr/local/etc/my/files/path/ssl_cert

Now edit your /etc/nginx/conf.d/mysites.conf and add this into the server {…} directive to make available example.com/.well-known url (3):

        location ^~ /.well-known {
                alias /usr/local/etc/my/files/path/ssl_cert/.well-known;
                allow all;
        }

Now execute the script to install certificates for your domains. Remember to use the command with -d domain-without-www -d www-domain in this order. (4)

1. Install all needed dependencies for your system (via yum on RedHat based distro and apt on Debian based)
2. Generate a valid certificate

certbot-auto certonly -a webroot --webroot-path=/usr/local/etc/my/files/path/ssl_cert -d example.com -d www.example.com -d mysite.com -d www.mysite.com

An auto check will be performed and you will get a Congratulation message.

Now generate a strong Diffie-Hellman group with this command (5):

openssl dhparam -out /etc/ssl/certs/dhparam.pem 2048

Check syntax and if ok reload the nginx server to apply changes and . (6)

nginx -t
systemctl reload nginx

Auto-renewal

A certificate will be valid for a short period of time, e.g. 3 months.

To auto-renew the certificate for all of your domains, you should add the auto-renewal command to cron (7):

30 2 * * 0 /usr/local/sbin/certbot-auto renew >> /var/log/le-renew.log
35 2 * * 0 /etc/init.d/nginx reload

The command will be executed every sunday night, between 2.30-2.35am, when the certificate will be checked to be renewed if needed.

Enable SSL on nginx

To enable SSL on nginx, if you have already a mysite.conf file mapped for uncrypted connection on port 80. Inside the /etc/nginx/conf.d directory, copy the file as mysite_ssl.conf and:

Change all occurrences of:

listen 80;

to:

listen 443 ssl;

In this way nginx will listen to 443 port on SSL. Ensure you have this port available externally (firewall and/or Selinux audit2allow). (8)

In the original file, mysite.conf, you can delete all entries but you have to keep the well-know part (step 3). This will avoid errors by Let’s Encrypt script.

Add and enable cyphers. Here there’s a good cyphers list, reliable for compatibile but secure using TLS only. (9)

server {
    # the port your site will be served on
    listen      443 ssl;
    # the domain name it will serve for
    server_name example.com; # substitute your machine's IP address or FQDN
    ssl_certificate /etc/letsencrypt/live/mysite.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/mysite.com/privkey.pem;
    ##### Cyphers and SSL fine tuning #####
    ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
    ssl_prefer_server_ciphers on;
    ssl_dhparam /etc/ssl/certs/dhparam.pem;
    ssl_ciphers 'ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:AES:CAMELLIA:DES-CBC3-SHA:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!aECDH:!EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA';
    ssl_session_timeout 1d;
    ssl_session_cache shared:SSL:50m;
    ssl_stapling on;
    ssl_stapling_verify on;
    add_header Strict-Transport-Security max-age=15768000;
    ##### END Cyphers and SSL fine tuning #####
    # charset     utf-8; etc...
}

Test nginx syntax with:

nginx -t

and then reload nginx to apply changes (10), on CentOS:

systemctl restart nginx