Let’s Encrypt is a new 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 web servers.
In this tutorial, we will show you how to use the certbot
Let’s Encrypt client to obtain a free SSL certificate and use it with Nginx on CentOS 7. We will also show you how to automatically renew your SSL certificate.
Before following this tutorial, you’ll need a few things.
sudo
privileges. You can learn how to set up such a user account by following steps 1-3 in our initial server setup for CentOS 7 tutorial.example.com
, that domain must resolve to your server for the validation process to work. Our setup will use example.com and www.example.com as the domain names, so both DNS records are required.Once you have all of the prerequisites out of the way, let’s move on to installing the Let’s Encrypt client software.
The first step to using Let’s Encrypt to obtain an SSL certificate is to install the certbot
software on your server. Currently, the best way to install this is through the EPEL repository.
Enable access to the EPEL repository on your server by typing:
- sudo yum install epel-release
Once the repository has been enabled, you can obtain the certbot-nginx
package by typing:
- sudo yum install certbot-nginx
The certbot
Let’s Encrypt client is now installed and ready to use.
If you haven’t installed Nginx yet, you can do so now. The EPEL repository should already be enabled from the previous section, so you can install Nginx by typing:
- sudo yum install nginx
Then, start Nginx using systemctl
:
- sudo systemctl start nginx
Certbot can automatically configure SSL for Nginx, but it needs to be able to find the correct server
block in your config. It does this by looking for a server_name
directive that matches the domain you’re requesting a certificate for. If you’re starting out with a fresh Nginx install, you can update the default config file:
- sudo vi /etc/nginx/nginx.conf
Find the existing server_name
line:
server_name _;
Replace the _
underscore with your domain name:
server_name example.com www.example.com;
Save the file and quit your editor. Verify the syntax of your configuration edits with:
- sudo nginx -t
If that runs with no errors, reload Nginx to load the new configuration:
- sudo systemctl reload nginx
Certbot will now be able to find the correct server
block and update it. Now we’ll update our firewall to allow HTTPS traffic.
If you have a firewall enabled, make sure port 80 and 443 are open to incoming traffic. If you are not running a firewall, you can skip ahead.
If you have a firewalld firewall running, you can open these ports by typing:
- sudo firewall-cmd --add-service=http
- sudo firewall-cmd --add-service=https
- sudo firewall-cmd --runtime-to-permanent
If have an iptables firewall running, the commands you need to run are highly dependent on your current rule set. For a basic rule set, you can add HTTP and HTTPS access by typing:
- sudo iptables -I INPUT -p tcp -m tcp --dport 80 -j ACCEPT
- sudo iptables -I INPUT -p tcp -m tcp --dport 443 -j ACCEPT
We’re now ready to run Certbot and fetch our certificates.
Certbot provides a variety of ways to obtain SSL certificates, through various plugins. The Nginx plugin will take care of reconfiguring Nginx and reloading the config whenever necessary:
- sudo certbot --nginx -d example.com -d www.example.com
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:
OutputPlease choose whether HTTPS access is required or optional.
-------------------------------------------------------------------------------
1: Easy - Allow both HTTP and HTTPS access to these sites
2: Secure - Make all requests redirect to secure HTTPS access
-------------------------------------------------------------------------------
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 cert will
expire on 2017-10-23. 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 represent that the site is properly secured, usually with a green lock icon.
If you test your server using the SSL Labs Server Test now, it will only get a B grade due to weak Diffie-Hellman parameters. This effects the security of the initial key exchange between our server and its users. We can fix this by creating a new dhparam.pem
file and adding it to our server
block.
Create the file using openssl
:
- sudo openssl dhparam -out /etc/ssl/certs/dhparam.pem 2048
This will take a while, up to a few minutes. When it’s done, open up the Nginx config file that contains your server
block. In our example, it’s the default config file:
- sudo vi /etc/nginx/nginx.conf
Paste the following line anywhere within the server
block:
. . .
ssl_dhparam /etc/ssl/certs/dhparam.pem;
Save the file and quit your editor, then verify the configuration:
- sudo nginx -t
If you have no errors, reload Nginx:
- sudo systemctl reload nginx
Your site is now more secure, and should receive an A rating.
Let’s Encrypt’s certificates are only valid for ninety days. This is to encourage users to automate their certificate renewal process. We’ll need to set up a regularly run command to check for expiring certificates and renew them automatically.
To run the renewal check daily, we will use cron
, a standard system service for running periodic jobs. We tell cron
what to do by opening and editing a file called a crontab
.
- sudo crontab -e
Your text editor will open the default crontab which is an empty text file at this point. Paste in the following line, then save and close it:
. . .
15 3 * * * /usr/bin/certbot renew --quiet
The 15 3 * * *
part of this line means “run the following command at 3:15 am, every day”. You may choose any time.
The renew
command for Certbot will check all certificates installed on the system and update any that are set to expire in less than thirty days. --quiet
tells Certbot not to output information or wait for user input.
cron
will now run this command daily. All installed certificates will be automatically renewed and reloaded when they have thirty days or less before they expire.
For more information on how to create and schedule cron jobs, you can check our How to Use Cron to Automate Tasks in a VPS guide.
In this tutorial we’ve installed the Let’s Encrypt client certbot
, downloaded SSL certificates for our 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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Doesn’t work. I see this:
I have followed the tutorial . All my configuration are fine but when I try to reach my domain via Https as it is said in the STEP 3 , nothing happens . And The SSL report returns : Assessment failed: Unable to connect to the server
Great tutorial, thanks! Just a question… using cloudflare DNS, do I have to disable their services also for renewals or only for installation?
Great tutorial. Thank you, Mitchell. It helped me a lot. However, I got straight an A rating. No need to update Diffie-Hellman parameters. Maybe it’s time to revise this part.
I had all of this working, but then noticed that
sudo certbot renew
commands had stopped working. Does anyone have experience troubleshooting this kind of error…Thank you ! very clear tutorial
Great write-up.
Step 5 may no longer be needed for current installations. The Certbot script seems to update ssl_dhparams. There is now a line included that states:
wow , what great article! thank you for the help ~
I’m facing 403 forbiden after install. here my error log:
2017/07/18 11:11:43 [error] 20200#0: *365 directory index of “/usr/share/nginx/html/” is forbidden, client: xxxxxxxxxx, server: xxxxxxxxxxxx, request: “GET / HTTP/1.1”, host: “xxxxxxxxxxxxxx”
Anyone can drive me?
Thanks.
Great write-up. Just thought I’d add for those using Nginx 1.13, you can now add TLSv1.3 to your SSL protocols.