How do you manage environment variables in a MERN stack project?

September 01, 2025

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🔹 What are Environment Variables?

Environment variables store configuration values (like database credentials, API keys, server ports) outside your codebase. This avoids hardcoding sensitive data.

🔹 How to Manage Environment Variables in MERN

1. Backend (Node.js + Express)

Install dotenv:
```
npm install dotenv
```

Create a .env file in the project root:


PORT=5000
MONGO_URI=mongodb+srv://user:password@cluster/mydb
JWT_SECRET=mysecretkey

Load variables in server.js:


require("dotenv").config();

const express = require("express");
const app = express();

const PORT = process.env.PORT || 5000;
const mongoURI = process.env.MONGO_URI;

app.listen(PORT, () => console.log(`Server running on port ${PORT}`));

✅ Never commit .env to GitHub — add it to .gitignore.

2. Frontend (React)

Create a .env file in the React project root:


REACT_APP_API_URL=http://localhost:5000/api

Use it in your code:


const API_URL = process.env.REACT_APP_API_URL;
fetch(`${API_URL}/users`)
  .then(res => res.json())
  .then(data => console.log(data));

⚠️ Important: React only exposes variables prefixed with REACT_APP_.

3. Deployment Considerations

Heroku / Render / Vercel / Netlify → Define environment variables in the platform’s dashboard.
Docker → Use docker-compose.yml or pass env vars in Dockerfile.
CI/CD pipelines (GitHub Actions, GitLab CI) → Store secrets in pipeline settings.

🔹 Best Practices

✔ Keep .env files out of version control.
✔ Use different .env files for dev, test, and production (.env.development, .env.production).
✔ Rotate API keys/secrets regularly.
✔ Document required environment variables for your team.

👉 In short:
In a MERN stack project, you use .env files + dotenv in the backend, REACT_APP_ variables in the frontend, and platform settings in production to safely manage environment variables.

What is server-side rendering (SSR) in React, and how does it help performance?

How do you deploy a MERN stack application?

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