One of the reasons for using MongoDB is its simplicity in scaling its structure,  either as Replicaset(scale-up) or as Sharded Cluster(scale-out). Although a bit tricky in Sharded environments, the reverse process is also feasible. From the possibilities, you can: Reduce the number of shards from your Sharded Cluster as documented here. You can also reduce the [&]

https://www.percona.com/blog/mongodb-converting-replica-set-to-standalone/