[govideo]

Thanks for everyone's perspectives. Very educational and admittedly lots outside the boundaries of my current knowledge. I have thus far relied on CloudFlare's automatic https and simple instant subdomain setup for their worker microservice I'm using.

There are evidently technical/footprint implications of that convenience. Fortunately, I'm not really concerned with the subdomain being publicly known; was more curious how it become publicly known.

[groestl]

I had to scroll pretty far down to see the first comment refering to the second most likely leak (after certificate transparency lists): Some ISP sold their DNS query log, and your's was in it.

People buying such records do so for various reasons, for example to seed some crawler they've built.