Linux

Secure Nginx with Let’s Encrypt on Ubuntu 18.04 with DNS Validation

How do I install and secure Nginx with Let’s Encrypt on Ubuntu 18.04 with DNS validation API? My domain DNS hosted with Cloudflare. How do I install Let’s Encrypt to create SSL certificates with Nginx web server running on an Ubuntu Linux 18.04 LTS server?

Introduction: Let’s Encrypt is an SSL certificate authority. One can get a free SSL/TLS certificate with it. Let’s Encrypt root, ISRG Root X1 directly adopted by Microsoft, Google, Apple, Mozilla, Oracle, Blackberry and other vendors. This page shows how to secure Nginx with Let’s Encrypt on Ubuntu 18.04 and use DNS to validate your domain to obtain an SSL/TLS certificate.

Secure Nginx with Let’s Encrypt on Ubuntu 18.04 with DNS Validation

The procedure to install Let’s Encrypt to create SSL certificates is as follows:

  1. Install acme.sh client
    git clone https://github.com/Neilpang/acme.sh.git
  2. Configure Nginx for SSL/TLS
  3. Configure UFW (firewall) to open port 443
  4. Issue SSL/TLS certificate for your domain using DNS validation method
  5. Install SSL/TLS certificate and restart Nginx server
  6. Validate cron job that will renew certificate automatically

Let us see all steps in details.

Step 1. Install acme.sh client

Naturally, the first step is to install the acme.sh software to get an SSL certificate. Install requied software using the apt command or apt-get command:
$ sudo apt-get install git bc wget curl
Install acme.sh software dependencies on Ubuntu 18.04

Clone the repo

$ cd /tmp/
$ git clone https://github.com/Neilpang/acme.sh.git

Install acme.sh client

$ cd acme.sh/
$ sudo -i
# ./acme.sh --install

How to install acme.sh Let's Encrypt client on Ubuntu 18.04 LTS
After install, you must close current terminal and reopen again to make the alias take effect. Or simply type the source command:
$ sudo -i
# source ~/.bashrc
# acme --version

Find out acme.sh client version

Step 2. Configure Nginx server for SSL/TLS

Use the mkdir command to create directories to store certificate for our domain named cms.cyberciti.biz:
# mkdir -pv /etc/nginx/ssl/letsencrypt/cms.cyberciti.biz/

Generate dhparams.pem file

You are going to use a strong Diffie-Hellman (DH) group, regardless of the server software. Run the openssl command to speed up dhparams generation on Ubuntu 18.04 LTS:
# cd /etc/nginx/ssl/letsencrypt/cms.cyberciti.biz/
# openssl dhparam -out dhparams.pem -dsaparam 4096

Create a strong Diffie-Hellman (DH) group dhparams.pem file

Configure TLS/SSL on Nginx web Server

Update a file named http.cms.cyberciti.biz.conf using a text editor such as nano command or vim command for both port 80 and 443:
# nano /etc/nginx/sites-available/https.cms.cyberciti.biz.conf
OR
# vim /etc/nginx/sites-available/https.cms.cyberciti.biz.conf
Append the following config:

Step 3. Issue and create an SSL Certificate on Ubuntu for Nginx using DNS method

DNS method allows you to issue an SSL/TLS certificate when having multiple web server running behind a load balancer. You need to use API provided by your DNS service provider to use the DNS validation method with Let’s Encrypt. Here is a list of supported DNS providers:

  1. GoDaddy, Cloudflare, Azure DNS, PowerDNS
  2. OVH/kimsufi/soyoustart/runabove, DNSMadeEasy
  3. AWS Route53, ISPConfig, Linode, Gandi, DigitalOcean, CloudDNS and more
  4. See complete list here

Cloudflare DNS example

For demonstration purpose, I am going to use Cloudflare DNS. First, get your Cloudflare API keys by visiting this page. Type the following commands:

Let’s issue a cert for domain cms.cyberciti.biz

The syntax is:
# acme.sh --issue --dns dns_cf -d www.example.com
# acme.sh --issue --dns dns_cf -d www.example.com -d subdomain.example.com
## wild card certicate
# acme.sh --issue --dns dns_cf -d *.example.com
# acme.sh --issue --dns dns_cf -d cms.cyberciti.biz

Secure Nginx with Let’s Encrypt on Ubuntu 18.04 with DNS Validation

Install the issued certificate to Nginx web server

It is time to install certificate and reload the nginx server:
# acme.sh --installcert -d cms.cyberciti.biz
--keypath /etc/nginx/ssl/letsencrypt/cms.cyberciti.biz/ssl.key
--fullchainpath /etc/nginx/ssl/letsencrypt/cms.cyberciti.biz/ssl.crt
--reloadcmd 'systemctl reload nginx'

Install Let's Encrypt Free SSL and TLS certificate in Ubuntu for Nginx

Test it

Open Nginx server tcp port # 443 if not already opened using the ufw command based firewall:
$ sudo ufw allow https comment 'Open all to access Nginx port 443'
Fire a web browser and type the url:
https://cms.cyberciti.biz/
Or visit SSL labs to test your TLS/SSL config:
cms.cyberciti.biz SSL labs report

How do I renew a certificate?

# acme.sh --renew -d cms.cyberciti.biz

A note about cron job

A cron job will try to do renewal a certificate for you too. This is installed by default as follows (no action required on your part):

How do I upgrade acme.sh client?

# acme.sh --upgrade

Conclusion

There you have it, you just secure Nginx with Let’s Encrypt on Ubuntu 18.04 with DNS validation. You installed Let’s Encrypt free SSL/TLS certificate. You learned how to install acme.sh client, issue SSL certificates for given domain name, configured Nginx. For more info see acme.sh client project page here.

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