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Networking Infrastructure: Dynamic DNS

Dynamic DNS (a.k.a. DDNS) services automatically update DNS records whenever a device's public IP changes, so that there is a consistent way to access a device which might not have a persistent public IP. There are various DDNS providers out there, both free and paid. When setting up DDNS on my RHEL EC2 instance, I found the free DDNS provider YDNS.io to be quite easy to use, but I've since switched to DuckDNS, because it sets all subdomains of the domain automatically.

Note: I've noticed when testing this that it can take a few minutes for the update to the DNS record to propagate.

DuckDNS

DuckDNS is a great service, in my experience. It does the same thing as YDNS, but it also automatically sets all subdomains of each of your subdomains (subsubdomains?) to the same ip as the subdomain.

  1. Log in to DuckDNS using a Google, Twitter, or GitHub account, then add a domain.

  2. Go to the DuckDNS install instructions, and select an install method, and follow the instructions.

While I originally recommended this method, I don't anymore. YDNS and DuckDNS both limit you to five subdomains, DuckDNS automatically sets all subdomains of that subdomain as well.

  1. Create an account on YDNS.io

  2. Launch the EC2 instance you want to configure

  3. On your YDNS account home, click the + New Host button, choose a domain from the dropdown menu, and enter a name, then enter the EC2 instance public IP Address in the content field.

Linux

This section assumes you are logged in as root. If not, switch to root with sudo -i, sudo -s, or equivalent.

  1. Install cURL, if necessary, then run the following: curl -o /root/ddns-updater.sh https://raw.githubusercontent.com/ydns/bash-updater/master/updater.sh

  2. Set the permissions to 700 for ddns-updater.sh: chmod 700 ddns-updater.sh

  3. Edit ddns-updater.sh, so that the values of $YDNS_USER and $YDNS_PASSWD reflect either your login or api credentials, and the change the $YDNS_HOST value to reflect the name and domain you chose in Step 2

  4. Edit your crontab with crontab -e, and add the line @reboot /root/ddns-updater.sh &>/dev/null

Windows

  1. Download and install DDNS Updater

  2. In the configuration window, enter your credentials, and set the IPv4 Update URL to "https://ydns.io/api/v1/update/?host=example.ydns.eu" (replacing "example.ydns.eu" with the name and domain you chose in step 2)

  3. (Optional) Set the External check URL to "https://ydns.io/api/v1/ip"