2. Environment & Config

Why configuration matters

Every environment (local development, testing, production) needs different credentials and URLs. Environment variables let us change behavior without editing source code.

Environment variable basics

Environment variables are key/value pairs that live outside of your code. Example: MONGODB_URI=mongodb://localhost:27017/tasks.
NestJS reads them through process.env. We’ll pass these values into MongooseModule.forRoot so the app knows which MongoDB to connect to.
Never hardcode secrets (passwords, API keys) inside .ts files. Store them in environment variables instead.

Using `.env` files

.env files are plain text files you load in development to set environment variables automatically.
We add a non-secret template named .env.example so new developers know which variables they must define.
Local files such as .env.development.local stay out of version control and contain your personal values.
In production, we use AWS Parameter Store / Secrets Manager (see Configuration & Environment).

Local vs. cloud MongoDB

Run MongoDB locally via Docker for quick feedback. You will create docker-compose.dev.yml in this chapter.
Use MongoDB Atlas when you can’t run Docker or want a hosted option. You’ll paste the Atlas connection string into the .env files created here.

After reviewing these ideas, continue to Prepare MongoDB to stand up Docker or Atlas and capture your .env settings, then move on to Connect MongoDB for the NestJS wiring.

Version control: branch for Chapter 2

Run the following commands before making changes so your work lives on a dedicated branch that can become a pull request:

git checkout main
git pull origin main
git checkout -b feature/environment-config

Commit as you go; you’ll push this branch and open a PR after finishing the chapter.