Introduction: Most of the case's applications are going to communicate with more than one database. Here I'm going to walk through with sample NestJS application which communicates with multiple MongoDB's. Click here to know more about NestJS API CRUD using MongoDB . MongoDB Atlas: MongoDB Atlas is a cloud database. It has all the options of creating a MongoDB instance like for Free MongoDB Instance(for learning), Paid MongoDB Instance(for production). To illustrate multiple MongoDB connections for sample application here I'm going to use this Cloud MongoDB Atlas. It is fairly minimal steps involved for created a Cloud MongoDB instance. Note: It is not mandatory to use the cloud based MongoDb database. You can use either locally installed instances like Mongo Shell, MongoDb Compass. Create Sample NestJS Application: NestJS provides CLI which helps to create a boilerplate templated application to getting started NestJS CLI command: np