Neat project! Setting up your own DNS server for a throwaway domain is definitely a pain, especially if you've never done so and use anything other than PowerDNS really, so this is useful for messing around with.
I do hope the author has set some limits on the DNS configuration you can freely enter. One annoying trick DDoS spammers will use is that they will set up DNS records that are as large as possible to use for their botnet's amplification attack, so allowing them arbitrarily large requests on your domain may be problematic and may cause nasty complaints against your domain. I'd recommend anyone running a free subdomain service (or something super cool like this!) to consider this in their configuration. We can't have nice things because of these bad people :(
CoreDNS which is commonly used in Kubernetes as a caching DNS server also supports RFC zone files and is very easy to configure. Written in Go, with just a few system library dependencies. I use it for LAN domains + cache + DoT client and it works nicely. I would probably not use it for big production deployments but it actually even supports master-slave transfers. :) Maybe worth having a look at this too.
I do hope the author has set some limits on the DNS configuration you can freely enter. One annoying trick DDoS spammers will use is that they will set up DNS records that are as large as possible to use for their botnet's amplification attack, so allowing them arbitrarily large requests on your domain may be problematic and may cause nasty complaints against your domain. I'd recommend anyone running a free subdomain service (or something super cool like this!) to consider this in their configuration. We can't have nice things because of these bad people :(