title: How to monitor Mongoose connection pool
body: <p>There's probably an obvious answer to this, but I can't seem to find it. I'm using Mongoose in my node app to connect to a MongoDB cluster. Is there any way to monitor the state of the client-side connection pool that Mongoose uses? Like a number of connection in the pool, number of connections currently checked-out from the pool, the rate at which connections are checked-out, etc? Bonus points if there's already a well established solution of exporting these metrics in Prometheus format.</p>