When deploying a MongoDB instance, there is a couple of important decision that has to be made. An important one is a decision whether the instance is going to be a Replica-set or a Sharded Cluster. It’s not uncommon to start with a Replica-set, as its easier to deploy and simpler to operate. For some workload, the Replica-set instance may not be the best option, mainly performance-wise, and the migration to a sharded cluster is the only way. This presentation will review the challenges when migrating from a Replica-set instance to a Sharded cluster. We will demonstrate real-world issues that users have encounter when migrating from a Replica-set to a Sharded cluster. We are going to list best-practices for the migration and the changes that may be required when moving to a Sharded cluster.