I got curious what all the traffic was, so I added a route to the API that saved some of the uploaded data. It was live home surveillance video and photos! Indoors, outdoors, baby monitors, living rooms, etc. It was pretty easy to find which vendor's hardware was doing this (from headers, paths, watermarks) and I reached out to their security contact to let them know what I found. They responded generically but didn't seem to care that much.

In short, because HTTPS was required, and an ELB gets assigned IPv4 addresses arbitrarily, I can only conclude that a whole fleet of home security cameras were sold across the US that hard-coded the IP address of their cloud server and had certificate validation disabled.

And it wasn't even raining outside! So I grab some plastic to cover the racks and phone in emergency portable cooling as the room's AC started failing.

It turns out earlier that day, a technician performing seasonal maintenance on a boiler tank on the roof had drained the tank and refilled it. But instead of directing the water out into a proper drain, he sent it down a convenient pipe that was actually a vent from our ceiling into the boiler house. The boiler was dozens of meters from my server room, but the water followed the old steel and plaster ceiling remnants over to my computers.

And this boiler water was more exciting than rain: it came with all the dissolved minerals, metals, and preservatives computers crave! I didn't lose any computers in the racks, but it killed the Liebert's control board.