Summary

Quoting Shard Replica Sets from the MongoDB 3.6 release notes:

Starting in MongoDB 3.6, mongod instances with the shard server role must be replica set members.

Load balancers are used with MongoDB 5.0+. Thus, drivers can assume that any load balancer is backed by a sharded cluster with replica sets and features such as change streams and transactions will be supported. It would be helpful to remind readers of this when introducing the "load-balanced" topology in the Unified Test Format spec.

This will not require any driver changes.

This issue came out of a Slack thread in #dbx-devs.

Motivation

Who is the affected end user?

Driver developers.

How does this affect the end user?

The documentation for load-balanced topologies can be improved to remind developers that all LB topologies are backed by sharded clusters with replica sets.

Is this issue urgent?

No.

Is this ticket required by a downstream team?

No.

Is this ticket only for tests?

Yes.