The Basic Idea of Servers

At its core, you’ve got it mostly right: a server is essentially a process that listens for requests and sends responses. But how you use different servers in your development workflow can vary, and that’s where terms like “web server” and “development server” come into play.

Web Server vs. Development Server

Web Server:

• A web server is designed to handle requests in a production environment. It serves static files (like your HTML, CSS, and JS) and typically interfaces with backend logic (like your Express API).
• When you deploy your app, the web server will serve your React build files (generated using npm run build) and facilitate requests to your backend API. Common tools for serving static files and APIs in production include Nginx, Apache, and Express.

Development Server:

• In contrast, a development server is primarily used to assist with building and testing your code locally during development. When you use Create React App, it spins up a development server using tools like Webpack. This server supports features like hot module reloading, fast rebuilds, and real-time updates—making it highly optimized for local development.
• It does not serve your app in production-ready form but is meant to make development more convenient.

Why Have Two Servers Running?

In many tutorials, you’ll see two servers running simultaneously:

1. Development Server (Client): Typically running on a port like 3000 via Create React App’s built-in tools.
2. Backend Server (Express): Running on another port, say 5000, and serving as your API layer.

This setup is common because:

• Separation of Concerns: Your React app focuses on rendering the UI and making requests, while the Express server handles API requests, authentication, database interactions, etc.
• CORS (Cross-Origin Resource Sharing): Since your frontend and backend are running on different ports, your React app makes requests to a different origin, which can be handled with appropriate CORS configurations in development.
• Easy Local Development: Having separate servers helps you develop the frontend and backend independently. For example, you can change your React code without restarting the backend and vice versa.

How This Looks in Practice

• In development, your Create React App’s development server handles requests for static assets and proxies API calls to your Express server (configured in package.json with "proxy": "http://localhost:5000").
• In production, you might have Express serve the built React files directly (e.g., by serving the contents of the build folder) along with handling API requests.

Example Flow

1. You run npm start in your React app. This starts the development server (e.g., on http://localhost:3000).
2. You run node server.js (or similar) for your Express backend, typically on a different port (e.g., http://localhost:5000).
3. Your React app makes requests to your Express server via fetch or axios calls to /api/some-endpoint. During development, these requests are proxied to http://localhost:5000 as per your configuration.

Quick Analogy

Think of your development server as a workbench where you can quickly build, tweak, and see updates, while your web server is more like a delivery person—it serves the completed product to users.

TL;DR: In development, you often have two servers—a React development server for fast frontend development and an Express server for backend logic. The dev server makes development fast and easy, while the backend server handles API requests. In production, you may consolidate and serve everything through one backend server.

Hope this clears things up! Cheers!