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5 · Real-World Architectures

10. Designing a Real-World Scalable System: Live Case Study

High-throughput URL shortener, distributed newsfeed generation, and real-time payment gateways.

12 min read · 3 MCQs

Requirements & Trade-Offs Matrix

A complete system design requires establishing functional requirements (what the system does), non-functional requirements (p99 latency < 50ms, 99.999% availability, idempotent transactions), high-level component topologies, and deep-dive failure mode analyses.

Fan-Out On Write vs Fan-Out On Read (News Feed)

Fan-out on write (Push model): When a user posts, append the post id directly to all followers' pre-computed timeline caches (fast reads, expensive writes for celebrities). Fan-out on read (Pull model): Aggregate followers' posts at read time (fast writes, slow reads). Hybrid models push for standard users and pull for celebrities.

Production Readiness Checklist

Before deploying a distributed architecture: ensure idempotent APIs with unique idempotency keys, configure health checks and connection pools, establish distributed tracing with OpenTelemetry, define SLOs with error budgets, and rehearse disaster recovery failovers.

Chapter quiz

3 questions · pass mark 75%

  1. 1. In a social media news feed, why is a pure 'Push' (fan-out on write) model problematic for celebrity accounts?

  2. 2. What is an idempotency key used for in payment APIs?

  3. 3. What does a hybrid fan-out model do in a social network?