Port

Detailed Explanation

A Port is a number (0-65535) that identifies a specific service running on a Server. Think of the server's IP address as a building address, and the port as the apartment number.

Common ports in web development:

• Port 80 — HTTP (standard web traffic)
• Port 443 — HTTPS (encrypted web traffic)
• Port 3000 — Common for Node.js development servers
• Port 5173 — Default for Vite dev servers
• Port 5432 — PostgreSQL databases

When you run npm run dev and see http://localhost:3000, the 3000 is the port your app is listening on. In Production, cloud services like Google Cloud Run assign a port via an environment variable (PORT), and your app must listen on whatever port is assigned.

A Dockerfile typically sets the port with ENV PORT=3000 and the app reads this value to know which port to listen on. The cloud platform then routes incoming traffic from port 443 (HTTPS) to your app's port.