I was going to say, that's absolutely nothing. They state 2.1K clusters and 16K nodes; if you divide those, assuming even distribution, you get 7.6 instances/cluster. Round down because they probably rounded up for the article, so 1 primary and 6 replicas per cluster. That's still only ~1400 QPS / cluster, which isn't much at all.
I'd be interested to hear if my assumptions were wrong, or if their schema and/or queries make this more intense than it seems.
I don't work for Uber, but this is almost certainly the assumption that is wrong. I doubt there is just a single workload duplicated 2.1K times. Additionally, different regions likely have different load.
I'd be interested to hear if my assumptions were wrong, or if their schema and/or queries make this more intense than it seems.