@oufok/env-reader

Use case

You might have an application that requires reading environment variables from different locations, depending on the run environment.

Let's think about an example:

• You want to share some env variables with other devs, and be able to add them to VCS (commit to git for example)
• You want to have the possibility to customise/define some variables per every environment, or machine. Example: local database username/password, settings whether to use a feature or not, etc
• You want to deploy your application in a container, so you can override those env variables through docker or kubernetes.

As a solution for those requirements, you can do the following:

• Define .env file and add it to git, where you add all env variables that can be shared across all environments
• Define .env.local file, and add it to .gitignore, so every user can use this to override generic variables, and add any env-specific variables.
• For containerized applications, you can still provide the variables you want to override via your orchestration system (like kubernetes) to override any values defined in .env or .env.local

If this solution works for you, then @oufok/env-reader is a perfect fit.

It provides the following functionality:

• Allows you to explicitly declare which env variables your application needs
• Reads requested env variables from process.env (global env variables, like one defined system wide, or provided from orchestration (docker/kubernetes,..) )
• For any missing variables, it falls back to the list of provided .env files and reads every variable from the first file that contains it.
• This allows you to specify override order as desired.
• Provides the possibility to explicitly fail if any requested env variables could not be found, so you can declare .env files as dependencies for your application.

##Usage example

const readConfig = require('@oufok/env-reader').readEnv;
const path       = require('path'); // just to join paths

// Assuming you add you have your .env files under ./config
let configDir = path.join(__dirname, './config');

const {
    REDIS_HOST,
    REDIS_PORT,
    DATABASE_HOST,
    DATABASE_PORT
} = readConfig(
    // Define all the env vars that you want to read, so env-reader can notify you if any of them is missing
    ['REDIS_HOST', 'REDIS_PORT', 'DATABASE_HOST', 'DATABASE_PORT'],
    [`${configDir}/.env.local`, `${configDir}/.env`], // the order matters, first file that contain the env var will be used
    true,  // skipMissingFiles, so different environments are free to add .env.local (for example) or not.
    false, // ignoreMissingKeys: false => don't ignore missing keys, i.e: throw an exception if any of the requested env vars is missing
);

This will try to read the requested env variables from global variables first (system-wide ones, like ones provided from kubernetes, ones defined in /etc/environment, etc).
Then, it will go through the provided list of .env files, and try to read the missing variables (ones which could not be found yet) from those files, one by one.
If multiple files contained the same var definition, the first value will be used.