That's a lot. With Percona clusters I started having issues requiring fine-tuning around a third of that at quite short peak loads, maybe ten minutes sustained high load topping out at 6-10k writes/s. Something like 24 cores, 192 GB RAM on the main node.
Not sure how GC works in Golang but if you see 20k writes/s sustained that's what I'd be nervous about. If every write is 4 kB I think it would be something like a quarter of a TB per hour, probably a full TB at edge due to HTTP overhead, so, yeah, a lot to handle on a single node.
Maybe there are performance tricks I don't know about that makes 20k sustained a breeze, I just know that I had to spend time tuning RAM usage and whatnot for peaks quite a bit earlier and already at that load planned for sharding the traffic.
