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Learn system design by reasoning

System design is the practice of turning an ambiguous product idea into a technical plan that can handle its expected load, remain available, and evolve safely. There is rarely one perfect answer. Good designs make their assumptions and trade-offs explicit.

A repeatable design process​

  1. Clarify requirements. Separate core user actions from nice-to-have features.
  2. Name the quality goals. Latency, availability, durability, consistency, cost, and security pull designs in different directions.
  3. Estimate scale. Orders of magnitude are enough to reveal the likely bottlenecks.
  4. Define contracts and data. Sketch APIs and the information the system owns.
  5. Draw the simplest complete design. Trace one request from the client to durable storage.
  6. Find the pressure points. Remove single points of failure and scale the hottest paths.
  7. Explain trade-offs. Say what your design optimizes and what it deliberately gives up.

Start with the prerequisites, then build your foundations with scalability and networking. Continue through databases, caching, and distributed systems. Finally, apply the model in the URL shortener case study.

Keep a decision log

For every major choice, write: decision, reason, alternative, consequence. That habit is more valuable than memorizing any architecture diagram.