I'm also interested in knowing more about this. How do you migrate an existing shard to a new one?
Well the data is presharded on a single instance using separate Redis databases so it's a simple process: - assuming Instance A has shards 0-99 on it and we want to split 0-49 to Instance A and 50-99 to Instance B - Setup Instance B with a complete replica of shards 0-99 - Update the shard map to point shards 50-99 to Instance B - Delete shards 50-99 from Instance A - Delete shards 0-49 from Instance B Since there are so many shards already we can divide up the data quite a bit, and new shards can be added at anytime as well. Adding shards rather than splitting them is the preferred strategy. We goal is to split as sparingly as possible.