> "Sharding is always something you do on day 1 for every project ... SPOF ..."

Cannot agree with that. If one does that or not, would depend on things like Service Level Agreements (SLA) — and one can have a pretty high SLA uptime %, without sharding, e.g. if there's an underlying pretty stable hosting provider that live migrates if there's a hardware failure.

Thanks for writing about the last time you used Redis. Interesting to hear that, in that case, the machines had sth like 64 – 128 RAM, and 250k – 500k RPS. Yes I agree that I'd need to benchmark and think about what type of machine(s) to use (some time later — a bit too early for that now). Sounds as if you are / were a pretty large company / project, needing that much memory and machines :- )