Why this guide?

This guide strips away the fluff and gives you the exact mental models, tradeoffs, and deep technical understandings required to ace Senior Backend and System Design interviews.

• Core Concepts: Auth, REST vs GraphQL, Idempotency.
• Databases: ACID, Transactions, Sharding, Locking.
• Caching & Scaling: Eviction, CDNs, Load Balancing, Microservices.
• Reliability: Race Conditions, Circuit Breakers, Sagas, Observability.