I am new to mongodb and wish to create a distributed database environment using docker-compose with mongodb. I've created multiple docker with shards to simulate multiple sites. However, I have a problem to replicate the same set of documents into multiple shards.

For example I have a collection with a key that has value "A" and "B". I want to distribute this collection into 2 shards where

Shard 1 = A & B  

Shard 2 = B only

However, when I run the balancer it distributes all A's into shard 1 and B's into shard 2. Is there any way I can do the sharding with repeated data or am I using the wrong approach for my problem?