Make the connection-pool used for egress connections from mongod to mongot have maximum and minimum sizes that are configurable by runtime-settable server parameters. Additionally, consider making configurable by server-parameters other properties of the pool, such as: 

• The maximum number of connections we are currently initiating/establishing/setting up concurrently, as a backpressur mechanism
• Any applicable monitoring parameters, such as how long connections can be idle before refresh, how long we will wait for a refresh  to complete successfully, and any strategy around dropping connections to a possibly down host.