Create Your Own Dynamic DNS Service

The more services I add to my NAS, the more I rely on it working. I recently moved my daughter's nightscout app to our server rather than hosting it on Heroku or some other service. It was actually working quite well... until my public IP address changed on me.

I'm not paying for a dedicated IP, but it has only changed once or twice in the past 5 years so I don't really worry about it changing. But recently it has changed twice in a week. The second time I was out of town, so fixing it involved a little more work. Because nightscout affects my daughter's health I want it up as much as possible.

I looked into some dynamic DNS services. But once I understood how they worked, I figured I could automate something simple myself. It turns out it was very simple.

Here is my shell script:

MYIP=$(dig +short myip.opendns.com @resolver1.opendns.com)
curl -u "$IWMN_USERNAME:$IWMN_PASSWORD" "https://iwantmyname.com/basicauth/ddns?hostname=$HOME_DOMAIN&myip=$MYIP&ttl=60"

What is it doing? The first line uses the dig command to get my public IP address and saves it as a variable. I then use that variable to call a simple API provided by my domain registrar (iwantmyname.com) to update my A record for that domain.

I then set up a cron job to run this script every night. If my IP address changes, things won't be broken for any more than 24 hours. Of course, I could run this more often if I want to ensure it is up to date.

Note that Synology does not have dig install by default. The quickest workaround for me was to install the DNSServer package. I then call dig via /var/packages/DNSServer/target/bin/dig.