This is a thing that needs to be said!

Many registrars don't provide an API to update your IP-addresses. This is a real pain when your server is located behind a dynamic IP address and you don't want to pay for decent Dynamic DNS services.

So here is how you do it for free. You just have to accept 10 minutes downtime due yo outdated DNS records. The keyword here is GoDaddy. GoDaddy is a registrar that provides an API for free. At least as long as you buy a domain from them.

Domeneshop.no, for instance, doesn't provide any API (at least per april 2019). Another different example is Loopia.no. They do provide an API, but only if you pay for their DNS hosting service, which is an additional 10 NOK/month on top of the domain registration fees.

The trick here is to use GoDaddy's name servers. You can host your .no domain on the GoDaddy DNS servers, even though you are a Loopia, Domeneshop or customer. You use your preferred national service to register national domains that aren't available throuh GoDaddy, and switch your name servers to GoDaddy in order to benefit from their free API service.

Then you simply clone this project, follow the instructions, and your on!

PS! The one drawback I can come up with (and it might not be small), is the lack of support for Internationalized Domain Names (IDNs) with GoDaddy. This poses a problem if you need to host domains with special characters in them.