Set up an FQDN for an SSL

What is an FQDN

Let's start with what a FQDN actually is. A Fully Qualified Domain Name simply specifies the exact location of a device/computer on the internet within the Domain Name System. The structure of an FQDN is: hostname . domain . tld . , where the last . is the root of the DNS namespace. Most DNS services and browsers automatically process the root . even if you do not include it.

Examples of a FQDN include:

host.example.com.
www.example.com.
anything.something.tld.

Configuring an FQDN

To configure an FQDN on your server, you should have:

1. An A Record configured in your DNS pointing the host to your server's public IP address
2. A line in your /etc/hosts file referencing the FQDN. See our documentation on the system's host file: Using Your System's hosts File

For instance, let's say my server's hostname is server1 and I want an FQDN to be server1.domain.tld. I would create an A record under my domain domain.tld with server1 as the host and the value as my public IP address. I would also edit the /etc/hosts file to input a line after the localhost line. Your host file may be different.

127.0.0.1 localhost
127.0.1.1 server1.domain.tld server1

FQDN in relation to SSL

In terms of configuring an SSL, many Certificate Authorities require that the common name for the certificate be an FQDN with a unique public IP address. This should also match with the URL of the site you're trying to obtain an SSL for.

Let's say I wanted to use www.domain.tld for my SSL. I would configure an A record on my DNS with the host as www and the value as a public IP address on my server. Your web server software, like Apache or Nginx, and other services will need to be configured to work with the domain and certificate registered for the SSL.

so an example would be?

127.0.0.1 linode.com
127.0.1.1 www.linode.com www

is that correct?

Yes, that would work for a host file to set 127.0.0.1 as the destination IP for linode.com and 127.0.1.1 as the destination IP for www.linode.com though in most cases the first thing set in the host file would be "localhost" and you'd normally want to set the www and non-www domains for the same site to the same IP address.

Thanks for the information