config.md

Externalizing the configuration

Till now, all configurations in our application is working for the local development environment, but they are written in hard codes.

In the development and deployment stages of a real world application, we have to consider a flexible way to alter the configurations in the production environment without any code changes while the application is deployed continuously through a predefined delivery pipeline.

Nestjs provides excellent configuration support, thus your application can read the configuration values from environment variables, a .env file, etc. More info about the configuration, check the Configuration chapter from the Nestjs official docs.

In this post, we will move our hard-coded configuration we've used in the previous posts to a central place and organize them with the NestJS configuration facilities.

Introduce to ConfigModule

First of all, install @nestjs/config package.

npm install @nestjs/config

Simply, import ConfigModule in the top-level AppModule.

import { Module } from '@nestjs/common';
import { ConfigModule } from '@nestjs/config';

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

It will register a ConfigService for you to read configuration properties by calling its get method.

configService.get<string>('MONGO_URI')

Internally, Nestjs will scan .env file in the root folder.

The following is a sample of the content of the .env file.

MONGO_URI=mongodb://localhost/blog

If you want to read configuration from an environment-aware file, eg. .dev.env for development phase, then configure the location in ConfigModule.

ConfigModule.forRoot({
  envFilePath: '.dev.env',
});

For the container deployment or cloud deployment, setup configuration in a config server or as environment variables or K8s ConfigMap is more popular.

Externalizing application configurations

Personally, I prefer use a default hard-coded configuration in the development phase, and use environmental variables to override it in the production.

Nestjs also support load custom configuration where it can read configurations from the environment variables freely.

In the AppModule, disable .env file support for ConfigModule.

@Module({
   imports:[
    	ConfigModule.forRoot({ ignoreEnvFile: true }),
	] 
})
export class AppModule{}

Then create a config folder to organize all configurations in this application.

In the config folder, add a new configuration for Mongo database.

//config/mongodb.config.ts

import { registerAs } from '@nestjs/config';

export default registerAs('mongodb', () => ({
  uri: process.env.MONGODB_URI || 'mongodb://localhost/blog',
}));

Here we use registerAs to group the configurations related to the context mongodb.

In the DatabaseModule, load the mongodb configuration.

import { databaseConnectionProviders } from './database-connection.providers';

@Module({
  imports: [ConfigModule.forFeature(mongodbConfig)],
  providers: [...databaseConnectionProviders,],
  exports: [...databaseConnectionProviders, ],
})
export class DatabaseModule { }

You can also use Nestjs ConfigModule to load the configuration globally, but here we do not want to expose the mongodb config to other modules.

And change the database connection providers like this.

import { ConfigType } from '@nestjs/config';
import { Connection, createConnection } from 'mongoose';
import mongodbConfig from '../config/mongodb.config';
import { DATABASE_CONNECTION } from './database.constants';

export const databaseConnectionProviders = [
  {
    provide: DATABASE_CONNECTION,
    useFactory: (dbConfig: ConfigType<typeof mongodbConfig>): Connection =>
      createConnection(dbConfig.uri, {
        useNewUrlParser: true,
        useUnifiedTopology: true,
        //see: https://mongoosejs.com/docs/deprecations.html#findandmodify
        useFindAndModify: false
      }),
    inject: [mongodbConfig.KEY],
  }
];

In the above codes, provide a token mongodbConfig.KEY, you can inject a config instance as type ConfigType<typeof mongodbConfig> in the factory method, then you can read the configuration in a type safe way via dbConfig.uri.

Similarly, create a configuration for the JWT authentication, move the existing JWT options into this configuration file.

//config/jwt.config.ts
import { registerAs } from '@nestjs/config';

export default registerAs('jwt', () => ({
  secretKey: process.env.JWT_SECRET_KEY || 'rzxlszyykpbgqcflzxsqcysyhljt',
  expiresIn: process.env.JWT_EXPIRES_IN || '3600s',
}));

In the AuthModule, apply the configuration like this.

import { ConfigModule, ConfigType } from '@nestjs/config';
import jwtConfig from '../config/jwt.config';

@Module({
  imports: [
    ConfigModule.forFeature(jwtConfig),
    ...
    JwtModule.registerAsync({
      imports: [ConfigModule.forFeature(jwtConfig)],
      useFactory: (config: ConfigType<typeof jwtConfig>) => {
        return {
          secret: config.secretKey,
          signOptions: { expiresIn: config.expiresIn },
        } as JwtModuleOptions;
      },
      inject: [jwtConfig.KEY],
    }),
  ],
....
})
export class AuthModule {}

And open jwt.stretagy.ts file, change the value of secretOrKey to read from jwtConfig.

import jwtConfig from '../../config/jwt.config';
import { ConfigType } from '@nestjs/config';
//...

@Injectable()
export class JwtStrategy extends PassportStrategy(Strategy) {
  constructor(@Inject(jwtConfig.KEY) config: ConfigType<typeof jwtConfig>) {
    super({
      jwtFromRequest: ExtractJwt.fromAuthHeaderAsBearerToken(),
      ignoreExpiration: false,
      secretOrKey: config.secretKey,
    });
  }
  //...
}

In a production environment, it is easy to change these settings by simply declaring an environment variables like this.

export MONGODB_URI=mongodb://localhost:27019/blog

Or set it in the docker-compose file like this.

version: '3.8' # specify docker-compose version
services:
  //...  
  api:
    environment:
      - "MONGODB_URI=mongodb://mongodb:27017/blog"
	//...

We will start a new topic of deployment in the further posts.

Testing configurations

An example of jwt-config.spec.ts.

import { ConfigModule, ConfigType } from '@nestjs/config';
import { TestingModule, Test } from '@nestjs/testing';
import jwtConfig from './jwt.config';

describe('jwtConfig', () => {
  let config: ConfigType<typeof jwtConfig>;
  beforeEach(async () => {
    const module: TestingModule = await Test.createTestingModule({
      imports: [ConfigModule.forFeature(jwtConfig)],
    }).compile();

    config = module.get<ConfigType<typeof jwtConfig>>(jwtConfig.KEY);
  });

  it('should be defined', () => {
    expect(jwtConfig).toBeDefined();
  });

  it('should contains expiresIn and secret key', async () => {
    expect(config.expiresIn).toBe('3600s');
    expect(config.secretKey).toBe('rzxlszyykpbgqcflzxsqcysyhljt');
  });
});

Grab the source codes from my github, switch to branch feat/config.