ConfigLoader

Utility class/functions to help load config from various sources.

Initial implementation narrowly supports AWS Lambda, but may be expanded to additional uses cases in the future.

Usage

The ConfigLoader class takes a type argument to strongly define the expected config variable names. Because the config can be loaded from multiple sources, there is no check of the existence of every variable until is is attempted to be used.

To use the loader, create a small file like this:

import { Context } from 'aws-lambda';
import { ConfigLoader } from '@rlmartin/config-loader';

export interface Config {
  readonly FOO: string;
  readonly BAR: string;
}

var config: ConfigLoader<Config>;

export async function loadConfig(context: Context) {
  config = new ConfigLoader<Config>(context);
  await config.load();
}

export function getConfig(key: keyof Config): Config[typeof key] {
  return config.get(key);
}

then when config is needed:

import { Context, S3Event } from 'aws-lambda';
import { getConfig, loadConfig } from './config';

export async function handler(event: S3Event, context: Context): Promise<void> {
  await loadConfig(context);
  const foo = getConfig('FOO');
  // ...
}

Supported config sources

The config is loaded from all of the following sources, in order of precedence (higher will override lower):

1. Secrets Manager
2. Environment variables (process.env)

Secret name

The secret name matches the AWS Lambda function name.

Nested secrets

It is possible to load values from other secrets by setting the value to:

{
  'propertyName': { '$ref':'secretName' }
}

where secretName is the name of the secret that should be loaded as the value for propertyName. The value in the dependent secret can be any value (JSON or otherwise). This loading is recursive.

Be careful to not load too many dependent secrets and/or nest too deeply - because a) SecretsManager pricing is based on the number of secrets loaded and b) it could adversely affect load times.

This same secret-loading process can be utilized by env vars, e.g.

process.env['propertyName'] = '{"$ref":"secretName"}';