Current version of the Node driver (at time of writing) considers maxPoolSize to be an absolute, that is, the specified number of connections must be established to the primary member (and auth'ed if needed) before connection is considered to be complete (see NODE-493 "Works as Designed").

Aside from the misleading name of the parameter, most (if not all) other drivers use on-demand connection semantics which expand the pool up to the limit as connections are concurrently employed.

The existence of the minPoolSize parameter (even if many drivers do not implement it) is instructive in that it only has meaning if maxPoolSize is treated as a limit rather than a target.

This ticket is to request the Node driver match the pooling behavior that C# and Java (and other drivers) implement.