Very nice ^^
One of the worst projects I’ve had to date was migrating a WHM installation from one server to another without root access on either machine and no cooperation from the hosts, so it ended up being a case of manually moving several hundred accounts over one by one.
I relied heavily on hacked together shell scripts calling dig similar to this to catch all of the inevitable problems (caused by other shells scripts hacked together to automate as much of the mind-numbing work as possible).
From the link, this doesn’t especially appear to check the DNS configuration. It just does a lookup. So nothing that dig and drill don’t already do well unless you like the ugly ASCII boxes. It’s also checking TLS certificate expiration on port 443. TLS is used on many other ports besides 443 and in general most proper monitoring systems will cover this. Or Let’s Encrypt will mail you if your renewal has failed and it gets late.
Nice. We wrote something similar (but with a smaller scope) at work a few years ago, because it was a real pain to check SSL expiry dates on a flaky cloud deployment (cloudfront ca 2016).