Building an API with NestJS #3: Adding Configurations

Introduction

An application, especially backend application, usually need some kind of configuration for it to work properly. This configuration could hold public or sensitive information such as our database connections, caching, feature flags, and so on. We can even make so that our app will not be able to run if some configuration settings are missing.

Often times, we also need our app to run in different environments like development, staging, and production. Depending on the environment, we need to use different configuration settings.

Let's see how we can add this kind of configuration to our NestJS app.

Installing Dependency

First, we need to install the required dependency.

npm i @nestjs/config

Internally, this package is using dotenv.

Adding Your First Config

Create a new file called .env in your project root. And put your configuration in it. For example, let's store a PostgreSQL database configuration:

DATABASE_USER=postgres
DATABASE_PASSWORD=postgres
DATABASE_NAME=postgres
DATABASE_PORT=5432

The above config is just an example. You should replace it with your own config.

By default, @nestjs/config package will look for a .env file in the root directory of your application. If you don't want to use .env but prefer to use let's say a .env.local file, you can customize the package to read your custom file as well. I'll explain how in the next section.

Load Your Config

To load your config, first you need to import ConfigModule into your AppModule.

import { Module } from '@nestjs/common';
import { ConfigModule } from '@nestjs/config';
import { AppController } from './app.controller';
import { AppService } from './app.service';

@Module({
  imports: [ConfigModule.forRoot()],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

This method will load and parse your configuration. If you are using filenames beside .env, you can specify it in the ConfigModule.forRoot() like this:

ConfigModule.forRoot({
  envFilePath: ['.env.local', '.env.development'],
});

Using Your Config

To use your configuration within your module, you will need to import ConfigModule into the module that will use it.

@Module({
  imports: [ConfigModule],
  // ...
})

Then, inject it into your constructor:

constructor(private configService: ConfigService) {}

And we can use it like this:

const dbName = this.configService.get<string>('DATABASE_USER');

That's it! Now you have a working config for your app.