I have created a MongoDB Atlas deployment (replicaSet) with 3 nodes (1P, 2S), and I'm connecting to MongoDB from my node web app as explained here.

The problem is when my web app make a request (ex: a find) sometimes is created a new TCP connection others it reuses an existing one but TCP connections are never removed and it results in a lot of connections shown in mongoDB atlas metrics. ( it reached 225 connections in primary node )

I have read your FAQ Does TCP keepalive time affect MongoDB Deployments? and after that I changed that property to 120 (2 minutes) but the connections still not being removed.

Note:
1 - I am creating a singleton to access the DB only once in node web app.
2 - I cannot use the property maxIdleTimeMS because isn't available in nodeJS driver.
3 - This is also happening when I run node web app in windows 8.

Is this situation normal ? how can I make those connections be removed after completed ?

Regards