MongoDB is a popular NoSQL database that has become the favourite of developers and software industries. It has a flexible design, the ability to scale as data grows (horizontal scaling) and has strong search functionality. In this story, we will understand MongoDB's architecture and how it fits into the software development ecosystem to cater to data storage and retrieval needs with programming languages and tools like Kotlin, Scala and Android development.

Introduction to MongoDB

It is a document-based database that stores data in BSON format i.e., Binary JSON. BSON format is optimized for data storage and traversal. Unlike relational databases, MongoDB stores the data in documents. Documents stored in collections. So, a document is a key-value pair which makes it easy to represent the hierarchal relationships in data.

MongoDB offers features like – Document Model, Sharding, Replication, Authentication, Database Triggers, Time Series Data, Ad-Hoc Queries, indexing, and load Balancing. 

MongoDB is a versatile document-oriented database management system suitable for a wide range of applications.

Basically, MongoDB is easy to work with, fast high performant, very flexible, and supports a wide variety of data and queries. 

How MongoDB differs from traditional Relational Databases

• Data structure: MongoDB uses BSON format to store the data, while relational database uses structured tables to store the data in rows and columns.

• Scalability: MongoDB can scale horizontally easily, which means can distribute data across multiple servers, while relational databases typically scale vertically by increasing the hardware and storage capability

• Query Language: MongoDB uses document-based query language, while relational databases use structured query languages.

• Normalization and Denormalization: RDBMS use normalizations to split the data in multiple tables for consistency, while MongoDB recommends denormalization to increase the read performance, as it stores related data together.

• ACID transactions: MongoDB and relational database both support ACID properties i.e., Atomicity, consistency, Isolation and Durability.

• Performance: MongoDB offers faster read and write operations in enormous amounts of data thanks to the indexed BSON data format.

• Integration and Ecosystem: Whether it is MongoDB Atlas, or MongoDB Stitch (serverless platform), it serves for both client-server architecture and serverless architecture. While RDBMS cannot be used as serverless architectures.

MongoDB Architecture: -

Database Architecture means how a database can be used and integrated with applications. Here we are going to talk about 1-tier, 2-tier, 3-tier architecture.

1-tier architecture or Single Tier Architecture:

It says both the application and the database are on the same device. You cannot differentiate between the physical location of the database and the application using the database. So, there is a Realm Database by MongoDB (a kind of mobile database) can be used as a local database by the application in the Mobile device.

2-tier architecture or Client-Server Architecture

In this architecture, multiple clients can connect to the same database running on the server, this is called client-server architecture. This is more commonly used by desktop applications connected to centralized databases. e.g.: the internal employee attendance system interacts directly with the MongoDB database for check-ins and check-outs.

3-tier architecture or Three layered architecture

3-tier architecture basically consists of the client, the backend server and the database server (instance of MongoDB). This comes with greater scalability, security, and faster deployments. We can think of the client as the mobile application, the backend application as the Python-based application service, and the database server as MongoDB. Since it has three layers i.e., client, backend, and database that’s why it is called 3-tier architecture. MongoDB Atlas is a multi-cloud database by MongoDB.

MongoDB Atlas

MongoDB Atlas is the cloud-based database service offered by MongoDB. It can be hosted on different cloud providers like AWS (Amazon Web Services), GCP (Google Cloud Platform), and Microsoft Azure.

Here as we discussed about the architecture of the MongoDB database, MongoDB Atlas has three layers: Data layer, Application layer, Presentation layer.

Data Layer

This layer consists of the Database server. So here data is stored in the MongoDB Atlas hosted which can be hosted on the cloud or on multiple clouds if needed. It is responsible to let the application layer access the data stored in the database.

Application Layer

The Application layer is also called the middle layer. This is the backend API, which could be Python web service, NodeJS backend API, or any other application service that accepts the client requests and reads or writes the data to and from the database in the data layer and serves the response to the client application.

Presentation layer

This is the UI layer of the client application, which is user-facing, I mean the UI application. It could be a mobile application built by Kotlin, the React application, or an Angular Web App.

MongoDB Architectural Overview

So, we discussed so far is MongoDB is the document-based NoSQL database that stores the data in Binary JSON format (BSON). It is a highly scalable, available, flexible, and versatile database management system.

We have discussed the difference between the Relational Database Management System (RDBMS) and the NoSQL (MongoDB) database.

• MongoDB use BSON format to store the data, while relational database uses row and column structural format to store the data.

• MongoDB is horizontally scalable while RDBMS is vertically scalable.

• MongoDB use document-based query language, while RDBMS use SQL to query data.

• MongoDB believes in denormalized data while RDBMS recommends normalization of data.

• We also discussed the ACID properties, performance and tools like MongoDB Atlas and MongoDB Stitch (serverless database platform)

We discussed the 1-tier (application and database on the same device), 2-tier (client-server architecture), and 3-tier (client, application backend server, database server).

We also discussed the data layer(database), application layer (backend application) and presentation layer (client application).