I'm not related to OP, but thanks for this answer! It is not easy to find a clear answer like that for a complex problem. The first time I had to build somethi

I'm not related to OP, but thanks for this answer! It is not easy to find a clear answer like that for a complex problem. The first time I had to build something to scale at day one, it was a long research about databases, cluster/shard, architecture and everything else you described. It worked, but it'd been easier with an answer like this one!