The backend is mostly a single script (Lua in Valkey, driven by a Phoenix server) that processes every click one at a time. That means validating the round, rate-limiting, and decrementing the countdown, so there's exactly one winner and no lost or double-counted clicks! There's a bunch of extra stuff around stats, username moderation/autoclicker detection, that sort of thing, but the bulk of it is that one script. I wrote a full post about it here: https://wayfarer-games.com/blog/one-button-mmo/