API Gateway

This lesson covers API Gateway. Let us learn this step by step — no rush, no jargon first.

What you will learn

• What api gateway means — in normal words, not textbook words
• How it works step by step
• Code you can run today on your laptop
• Where teams use this in real projects

Before you start

• Software: Node.js LTS from nodejs.org, VS Code, and a terminal
• Knowledge: Earlier lessons in this Node.js course
• Previous lesson: Microservices — Complete Guide

Explain it simply

An API gateway is the single front door for clients — routing, auth, and rate limits in one place.

Why developers use this

• For larger teams and scale
• Learn concepts before you need them
• Helps system design talks

How it works (step by step)

1. Identify the real problem (scale, team size, CPU load).
2. Apply API Gateway to that problem only.
3. Keep observability: logs, metrics, health checks.
4. Load-test before and after so you know it helped.

Code example — type this yourself

app.use('/api/users', proxy('http://localhost:3001'));
app.use('/api/orders', proxy('http://localhost:3002'));

Tools: Express proxy, Kong, or cloud API Management.

What each part does

• app.use('/api/users', proxy('http://localhost:3001')); — Line 1: runs as written.
• app.use('/api/orders', proxy('http://localhost:3002')); — Line 2: runs as written.

Real life: where API Gateway shows up

A growing SaaS product introduces API Gateway only after the monolith gets painful — measured traffic, not guesswork, drives the change. In interviews, explain the trade-off you chose and what you would measure in production.

Try it yourself — hands-on

1. Create a new file (e.g. api-gateway-demo.js) in an empty folder
2. Type the example code for API Gateway yourself — typing helps memory
3. Run node on that file and read the output
4. Change one line (a value, a message, a route path) and run again to see what breaks or improves

Common mistakes (avoid these)

• Skipping the terminal — API Gateway only feels easy after you run code yourself.

Interview note

Senior interviews may ask how API Gateway behaves under load, failure, or security review — mention logging, timeouts, and validation.

Summary

• You can explain API Gateway in your own words
• You ran working code — not just read about it
• You know one mistake to avoid and one real place teams use this