Module 03: API and Communication

Welcome to Module 03. In the previous modules, we covered the basics of Networking and the Mindset of a System Architect. Now, we dive into the Language of Systems. How do services talk to each other? How do clients talk to servers?

🎯 Learning Objectives

By the end of this module, you will be able to:

  1. Design robust REST APIs using standard methods, status codes, and idempotency, and know when to switch to gRPC.
  2. Evaluate GraphQL and understand when to use it over REST (and avoid the N+1 problem).
  3. Implement Real-Time features using WebSockets, SSE, and Long Polling, with proper Exponential Backoff.
  4. Architect an API Gateway to handle rate limiting, auth, SSL termination, and routing.

📚 Chapter List

Chapter Topic Key Concepts
01 REST API Design Strategies CRUD, Idempotency, HATEOAS, OpenAPI, gRPC.
02 GraphQL Basics Schema, Resolvers, N+1 Problem, Federation.
03 Polling vs Push Short/Long Polling, WebSockets, SSE, Socket.IO, HTTP/3.
04 API Gateway Pattern Rate Limiting, Circuit Breakers, BFF, Service Mesh, SSL Termination.

🛠️ Prerequisite Knowledge

  • Basic HTTP (Headers, Body, Verbs).
  • Understanding of “Client-Server” architecture.
  • (Optional) Experience with Express.js or Spring Boot.

🚀 Interactive Labs

Each chapter in this module contains an Interactive Decision Visualizer.

  • REST Terminal: Send requests and see how the server responds.
  • N+1 Visualizer: Watch how GraphQL can kill your database.
  • Protocol Racer: Compare the latency of Polling vs WebSockets.
  • Gateway Policy Simulator: Act as a “Bouncer” for your backend.

Let’s begin with the lingua franca of the web: REST API Design.

Module Chapters