Red Hat/CentOS: How to add HTTPS to an existing Nginx website (both with and without Let’s Encrypt)

(Yes, you read the title correctly. For extra fun, and to prevent this blog from being too focused on Ubuntu/Debian, this time I’ll be using Red Hat Enterprise Linux / CentOS (and, I assume, Fedora as well.) Later on, I may post a Debian-based version.)

Configuring a basic HTTP site on Nginx

(Note: if you already have a working HTTP site, you can skip to the next section (“Adding encryption…”))

Yes, the post title mentions an “existing” website, which I believe will be the case in most “real world” situations, but installing a new one is actually very easy on CentOS1. First, do:

yum -y install epel-release; yum -y install nginx

Then create a very basic configuration file for the (non-HTTPS) site, as /etc/nginx/conf.d/mysite.conf :

server {
        listen 80;
        server_name mysite.mydomain.com;
        root /var/www/mysite;

        location / {
        }
}

Then, of course, create the /var/www/mysite directory (CentOS doesn’t use /var/www by default, but I’m far too used to it to change. ūüôā ) If you’d like, create an index.html text file in that directory, restart nginx (“service nginx restart” or “systemctl¬†restart nginx“, depending on your system’s major version), and try browsing to http://mysite.mydomain.com . If it works, congratulations, you have a running web server and a basic site.

Adding encryption to the site (not¬†using Let’s Encrypt):

First, you need a key/certificate pair. I have tutorials for creating an RSA certificate or an ECDSA certificate.

Second, edit the site’s configuration file (in the “starting from scratch” example above, it’s “/etc/nginx/conf.d/mysite.conf“), and copy the entire server section so that it appears twice on that text file (one after the other). Pick either the original or the copy (not both!), and, inside it, change the line:

listen 80;

to:

listen 443 ssl http2;

(Note: the “http2” option is only available in Nginx 1.9.5 or newer. If your version complains about it, just remove it, or upgrade.)

Inside that section, add the following options:

ssl_certificate /path/to/certificate.crt;
ssl_certificate_key /path/to/privatekey.crt;

(replacing the paths and file names, of course.)

This should be enough — restart Nginx and you should have an HTTPS site as well as the HTTP one.

And what if you want to disable HTTP for that site and use HTTPS only? Just edit the same configuration file, look for the¬†server section you didn’t change (the one that still includes “listen 80;“), and replace the inside of that section with:

listen 80;
server_name mysite.domain.com;
return 301 https://mysite.domain.com$request_uri;

Afterward, while you’re at it, why not go for an A+ rating on SSL Labs¬†(skip the certification creation part from that tutorial, you’ve done it already) and an A rating on securityheaders.io?

Adding encryption to the site (using Let’s Encrypt):

First, install certbot:

yum install python2-certbot-nginx

Then check if Nginx is running and your normal HTTP site is online (it’ll be needed in a short while, to activate the certificate). If so, then enter:

certbot --nginx --rsa-key-size 4096 -d mysite.mydomain.com

(replacing “mysite.mydomain.com” with yours, of course.)

Answer the questions it asks you: a contact email, whether you agree with the terms (you need to say yes to this one), if you want to share your email with the EFF, and finally if you want “No redirect” (i.e. keep the HTTP site) or “Redirect” (make your site HTTPS only).

And that’s it (almost — see the next paragraph) — when you get the shell prompt back, certbot will already have reconfigured Nginx in the way you chose in the paragraph above, and restarted it so that it’s running the new configuration. You may want to add “http2” to the “listen 443 ssl;” line in the configuration file (it’ll probably be the default someday, but as of this post’s date it isn’t), and don’t forget your options for improved security and security headers.

Only one thing is missing: automatically renewing certificates. Strangely, the certbot package configures that automatically on Ubuntu, but not on CentOS, from what I’ve seen (please correct me if I’m wrong). The official Let’s Encrypt docs recommend adding this (which includes some randomization so that entire timezones don’t attempt to renew their certificates at precisely the same time) to root’s¬†crontab:

0 0,12 * * * python -c 'import random; import time; time.sleep(random.random() * 3600)' && certbot renew 

(Note: It’s possible to use Let’s Encrypt to create ECDSA certificates, but as of this writing you have to do most of the work manually (creating a CSR, etc.), and you lose the automatic renewal, so for the moment I suggest using RSA certificates. I hope this changes in the future.)