Is there anything on how a multi-node cluster works (I'm kinda assuming there's something since it makes "single" mentions a few times)? Application-level shard

Is there anything on how a multi-node cluster works (I'm kinda assuming there's something since it makes "single" mentions a few times)? Application-level sharding is always an option (and multiple things I've worked on have used it to great effect), but anything automatic seems likely gnarly and fun to learn about, if it recovers some of the naive perf loss of "just hold the lock while doing rpc to other nodes".