0. To accept that there will be some simple and you will have to spend a lot of money.
1. To examine the existing database and to determine the keys for sharding.
2. To prepare your application code for use in the replica.
3. To convert the current database in a replicating set
4. To prepare your application to work with sharding, it should only work with the load balancer, and in any case not with the shard.
5. To convert a replica to a cluster
The Monge each shard contains a replica of himself.