Creating a Multi-Tenant Application with NestJS and MongoDB

In today’s cloud-driven world, multi-tenant applications are becoming increasingly popular. These applications allow multiple clients (or tenants) to share a single application instance while keeping their data isolated. This not only saves resources but also simplifies application management. In this article, we will explore how to create a multi-tenant application with NestJS and MongoDB, covering definitions, use cases, and actionable insights to help you build your own.

What is a Multi-Tenant Application?

A multi-tenant application serves multiple tenants from a single instance of the application, while ensuring data isolation among them. Each tenant can be a different business or organization, and their data is stored separately, typically using one of two approaches:

• Database-per-tenant: Each tenant has its own database.
• Shared database: All tenants share a single database, but their data is separated using a tenant identifier.

The choice of approach depends on factors like scalability, complexity, and performance requirements.

Use Cases for Multi-Tenant Applications

1. SaaS Platforms: Software as a Service (SaaS) applications often use a multi-tenant architecture to provide services to various clients.
2. Enterprise Solutions: Large organizations with multiple departments may use a multi-tenant architecture to manage their internal applications.
3. E-commerce Platforms: Multi-tenant e-commerce solutions allow different businesses to run their stores on a single platform while maintaining customer data privacy.

Why Choose NestJS and MongoDB?

NestJS

NestJS is a progressive Node.js framework for building efficient, scalable server-side applications. It leverages TypeScript and is designed to work with a modular architecture, making it easier to manage complex applications. Key features include:

• Dependency Injection: Simplifies management of dependencies.
• Modular Structure: Encourages code organization and reusability.
• Support for Websockets and GraphQL: Flexible for various application needs.

MongoDB

MongoDB is a NoSQL database that stores data in flexible, JSON-like documents. It is perfect for multi-tenant applications due to its scalability and ability to handle large amounts of data efficiently. Features include:

• Flexibility: Schema-less data storage allows for rapid development.
• Horizontal Scaling: Easy to scale out when your application needs grow.

Step-by-Step Guide to Building a Multi-Tenant Application

Step 1: Setting Up the Project

First, ensure you have Node.js and MongoDB installed. Then, create a new NestJS project:

npm i -g @nestjs/cli
nest new multi-tenant-app
cd multi-tenant-app

Install the required packages:

npm install @nestjs/mongoose mongoose

Step 2: Configuring MongoDB

In your app.module.ts, import the MongooseModule and set up your MongoDB connection:

import { Module } from '@nestjs/common';
import { MongooseModule } from '@nestjs/mongoose';
import { TenantModule } from './tenant/tenant.module';

@Module({
  imports: [
    MongooseModule.forRoot('mongodb://localhost/multi-tenant', {
      useNewUrlParser: true,
      useUnifiedTopology: true,
    }),
    TenantModule,
  ],
})
export class AppModule {}

Step 3: Creating the Tenant Module

Now, create a module to manage tenants:

nest g module tenant
nest g service tenant
nest g controller tenant

In tenant.schema.ts, define the tenant schema:

import { Prop, Schema, SchemaFactory } from '@nestjs/mongoose';
import { Document } from 'mongoose';

@Schema()
export class Tenant extends Document {
  @Prop({ required: true })
  name: string;

  @Prop({ required: true })
  identifier: string; // Unique identifier for each tenant
}

export const TenantSchema = SchemaFactory.createForClass(Tenant);

Step 4: Implementing Multi-Tenancy Logic

In tenant.service.ts, implement the logic to create and retrieve tenants:

import { Injectable } from '@nestjs/common';
import { InjectModel } from '@nestjs/mongoose';
import { Model } from 'mongoose';
import { Tenant } from './tenant.schema';

@Injectable()
export class TenantService {
  constructor(@InjectModel(Tenant.name) private tenantModel: Model<Tenant>) {}

  async createTenant(name: string, identifier: string): Promise<Tenant> {
    const newTenant = new this.tenantModel({ name, identifier });
    return newTenant.save();
  }

  async findAll(): Promise<Tenant[]> {
    return this.tenantModel.find().exec();
  }
}

Step 5: Creating API Endpoints

In tenant.controller.ts, create endpoints for managing tenants:

import { Controller, Get, Post, Body } from '@nestjs/common';
import { TenantService } from './tenant.service';
import { Tenant } from './tenant.schema';

@Controller('tenants')
export class TenantController {
  constructor(private readonly tenantService: TenantService) {}

  @Post()
  async create(@Body() createTenantDto: { name: string; identifier: string }): Promise<Tenant> {
    return this.tenantService.createTenant(createTenantDto.name, createTenantDto.identifier);
  }

  @Get()
  async findAll(): Promise<Tenant[]> {
    return this.tenantService.findAll();
  }
}

Step 6: Testing the Application

Run the application:

npm run start

Use Postman or any other API testing tool to test your endpoints. You can create tenants and retrieve them using the defined endpoints.

Troubleshooting Common Issues

1. MongoDB Connection Errors:

2. Ensure that MongoDB is running and accessible at the specified URL.

3. Mongoose Validation Errors:

4. Check if the data being sent to the API meets the schema requirements.

5. Dependency Injection Errors:

6. Make sure all necessary modules are properly imported and registered in the main application module.

Conclusion

Creating a multi-tenant application with NestJS and MongoDB is a powerful way to build scalable and efficient applications. With this guide, you have the foundational knowledge and code snippets to start developing your own multi-tenant architecture. As you grow your application, consider additional features such as authentication, role-based access control, and data analytics to enhance the user experience and functionality. Happy coding!