Multi tenancy - NodeJs- how to connect to several DBs properly?

We are working on converting several microservices to a multi-tenant approach.
We decided to go with the DB per tenant approach (same MongoDB server though)
We are facing a design issue - how to connect to several DB in one node (assuming elasticity will be available in the future).
Currently using MongoDB v4.4 (atlas in prod), NodeJs v14.16, MongoDB client v3.6.3
We have several hundred customers and will grow even bigger in the future.

we’ve managed to connect by creating a connection to the MongoDB server (without specifying a specific DB):

const mongoConnection = new MongoClient(mongoUrl, connectionOptions).connect();

Whenever there is a need to access a tenant DB and perform actions I’ll provide access to the right database by exposing this method:

function getConnection(tenantId) {
return mongoConnection.db(getTenantDbName(tenantId))

My questions:

  1. Is the connection pool shared between all databases?
  2. Is the right scale-out approach is to increase the shared connection pool whenever a new tenant is added or use a different connection pool for each tenant?
  3. Does the fact that we use mongo atlas in prod help us in any way?
  4. What are the things we have to take into consideration?

Check the link helps you Building a Multi-Tenant App With NodeJS + MongoDB | by Aman Agarwal | Geek Culture | Medium