What would be the backend setup of a popular MMO like e.g. Brawl Stars or Clash Royale be like?

I'm always wondering what would be the setup? I'm sure the game is not polling, but has an active connection to somekind of socket server. Could it be Node? And how would the matching system work? Would players be categorized by country and then matched by level? Would that mean having several vps instances on several continents?