I don't get it. Why are they using such a complicated infrastructure for something that can just be a static file polled by devices? Let's get nifty and maybe have a small php intermediary for slow roll. Assuming 10M devices, 24h polling sounds reasonable that's 10M requests/day. A VPS should be able to handle that.
(I'm saying this as someone who managed OTA for 1M smartphones that way 10yrs ago)