Module 03: Review & Cheat Sheet

Congratulations on completing Module 03! This module covered the fundamental ways systems talk to each other.

1. Key Takeaways

Concept The “One Liner”
REST Resource-based, stateless, standard HTTP verbs. Level 2 is the standard.
GraphQL Client asks for exactly what it needs. Solves Over-fetching.
gRPC High-performance RPC using Protobuf. Great for internal microservices.
Polling “Are we there yet?” Simple but high latency/overhead.
WebSockets Full-duplex persistent connection. Lowest latency. Stateful.
API Gateway The “Front Door”. Handles Auth, Rate Limiting, and Routing.
BFF Backend for Frontend. Tailored APIs for specific clients (Mobile vs Web).
Circuit Breaker Fails fast when a downstream service is down to prevent cascading failure.

2. Interactive Flashcards

Test your memory! Click to flip.

3. System Architect Challenge

Test your ability to choose the right tool for the job.

1. You are building a Stock Trading platform where milliseconds matter. You need to stream price updates to a dashboard.
2. Your mobile app needs to display a user profile, their last 3 orders, and their wish list. You want to minimize battery usage and requests.

4. System Design Checklist: API Choice

When designing a new system, ask these questions:

  • Who are the clients?
    • Mobile? (Use BFF, minimize data).
    • Internal Services? (Use gRPC).
    • Public Developers? (Use REST/GraphQL).
  • Is it Real-Time?
    • Yes, high frequency (Game)? → WebTransport/UDP.
    • Yes, chat? → WebSockets.
    • Yes, news feed? → SSE.
    • No? → REST.
  • Do we need Caching?
    • Yes, heavily? → REST (Leverage CDNs).
    • No, data changes per user? → GraphQL.
  • How do we handle failures?
    • Retries? → Implement Idempotency Keys.
    • Circuit Breakers? → Use a Service Mesh.

5. Next Steps

You are now ready to handle data storage. Proceed to Module 04: Database Basics or explore the Load Balancing module.