Yesterday it was 4 seconds from a LE cert -> scans for .env and other low hanging info leak/vulnerabilities from at least 4 different scanners.
There are groups out there just looking at the certificate transparency logs to get the newly added certs to scan.
Yeah, one of the reasons why I started to for all my dev side projects to be under a single wildcard subdomain, because I used to create new certs automatically with letsencrypt and everytime this spam happened. If I do things right it shouldn't matter, but I still feel better with the wildcard if I was to make a mistake...
Short related story: some customer wanted an API with a basic firewall, they said they don't need filter rules as it won't be used or something. I put a dumb API online (doing nothing) and showed them the request logs after one day. They approved the filter rules immediately.
Basically a simple server listening on a port will experience hundreds of random script-probing attacks per day. And if any of them show the slightest hint of succeeding then that escalates quickly to thousands per minute.
You don't need a DNS entry to "expose" the IP address (there are only 4 billion). Moving to another port reduces, but doesn't eliminate the traffic.
Telling people this freaks them out. But as long as the server is done well its just noise.