As far as I can understand, not all databases in a MongoDB shard cluster have to be sharded; I can keep some databases unsharded, on only one of the shards.
So suppose I have a shard cluster, with shards (i.e. replica sets)
rs0 has a database
foo, which is unsharded. I have no plan to shard it or move it to
Is there any harm in letting some clients connect to
rs0 directly and use the
foo database without going through mongos?
I have only tested that it is possible to connect directly to
rs0 and make queries in
foo, but I don't know if it is potentially dangerous in my use case.