Part 2 of “System Design Explained Like a Human.” This time, we explore how large-scale systems recover when the internet fights back.

💡 1. Fault Tolerance & High Availability

Systems continue running even if parts fail. Flipkart reroutes traffic to healthy zones within seconds.

Tools: Kubernetes health-checks, AWS ALB, Failover Groups.

🧯 2. Disaster Recovery & Data Replication

Keep live copies in different regions. Netflix stores in Mumbai + Singapore for failover.

🧩 3. Event-Driven Microservices

Services communicate via events instead of blocking calls. Example: Swiggy uses Kafka topics between Order, Payment, and Notification services.

⚖️ 4. CAP Trade-offs Revisited

Banking → CP

Social media → AP Choose what fits your business.

📬 5. Message Queues & Stream Processing

Queues smooth traffic spikes — like taking a token at the bank. Tools: RabbitMQ, Kafka, Amazon SQS.

🚧 6. Rate Limiting & Circuit Breakers

Protect services from overload and cascading failures. Libraries: Hystrix, Resilience4J.

🔐 7. Security & API Gateways

Auth every request via JWT / OAuth. Gateways also log, throttle, and audit traffic.

💸 8. Cost Optimization

Scale up during peak, scale down after. Use spot instances and reserved capacity.

📈 9. Monitoring & Alerting

Set SLO-based alerts on latency, error rate, and throughput. Stacks: Datadog, Grafana, Prometheus.

💥 10. Chaos Engineering

Inject controlled failures to test resilience. Netflix’s Chaos Monkey kills servers randomly.

🧠 11. Data Sharding & Replication Patterns

Shard by user ID / region / hash key to avoid hotspots. Replicate read-only copies for scale.

🌍 12. Global Systems & Edge Computing

Serve users from the nearest location. CDNs + edge caching reduce latency.

🩹 13. Auto-Healing Infrastructure

Kubernetes restarts failed pods automatically. No manual rebooting at 2 AM.

🍔 14. Real-World Case Study — Zomato Order Surge

Health check fails → Pod restarted

LB reroutes traffic

Auto-scaling adds instances Result: users see a short delay, no downtime.

🏁 Conclusion

From caching and queues to chaos and recovery, this two-part journey showed how modern apps scale and survive.

Great architecture isn’t about preventing failure — it’s about recovering so fast that no one notices.

If you liked this series, ❤️ it on DEV.to and share with your team. Let’s keep building systems that don’t just scale — they endure.