nestjs ConfigModule.forRoot() asynchronuous

Question

I want to load config in Nestjs from a configuration server with a REST API to allow for centralized application configuration. However there is no async version of the ConfigModule.forRoot() function so the configuration returns as undefined.

Is there any way around this ?

Answer 1

Solved by creating a factory function that returns a Nest ConfigService object

// config-factory.ts
import { ConfigService } from '@nestjs/config'
import axios from 'axios'

export async function getConfigService() {
  const host = ...
  const port = ...
  const configUrl = `http://${host}:${port}/config`
  const postData = ...
  const response = await axios.post<Record<string, any> | undefined>(configUrl, postData)

  return new ConfigService(response.data)
}

@Global()
@Module({
  controllers: [],
  providers: [
    {
      provide: ConfigService,
      useFactory: getConfigService,
    },
  ],
  exports: [ConfigService],
})
export class AppModule {}

Answer 2

According to the docs, you can inject a custom configuration file via the load parameter. Ordinarily, you would pass a synchronous factory function that returns a pre-generated object with the Record<string, any> format, but you can also pass an async factory function here, and your config will be loaded from the server before the application bootstrap without the need to inject the ConfigService as a Custom Provider (if you do that, the ConfigModule is not properly being registered in the App, you can't access it in the main.ts, and you can't use the ConfigModule options).

Example:

shared.module.ts

import { Module } from '@nestjs/common';
import { ConfigModule, ConfigService } from '@nestjs/config';
import { load } from './loadConfig';

@Module({
  imports: [
    ConfigModule.forRoot({
      isGlobal: true,
      load: [async () => load({})],
    }),
  ],
  providers: [],
  exports: [],
})
export class SharedModule {}

loadConfig.ts

import { SSM } from 'aws-sdk';

export const load = async (options: any): Promise<any> => {
  const test = new SSM({ region: 'eu-north-1' });

  const parameters = await test
    .getParametersByPath({
      Path: '/path/to/ssm/route/',
      Recursive: true,
    })
    .promise();

  return parameters
};