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Requirements and scope

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Requirements And Scope Deep Dive

Overview

Most failed design answers come from weak scope control, not weak technical knowledge.

Core Concepts

  • Functional requirements: user-visible capabilities.
  • Non-functional requirements: latency, reliability, throughput, security.
  • Explicitly de-scope nice-to-have features.

Internal Architecture

  • Scope determines architecture complexity.
  • Narrow scope allows simpler single-region design.
  • Broad scope may require eventing, partitioning, and regional strategy.

Data and Request Flow

  • Define top 2-3 critical flows first.
  • Add secondary flows only after core flow is stable.

Scalability and Reliability

  • Capacity targets should map to scope.
  • Reliability target (e.g., 99.9%) changes retry, storage, and failover choices.

Code Examples

Inputs: users, regions, RPS, payload, freshness
Outputs: service topology, storage choice, scaling strategy

Common Interview Questions

  • Q: How do you gather requirements quickly? A: Structure the answer as constraints then tradeoffs: SLOs, capacity assumptions, bottlenecks, failure modes, and mitigation plans with clear triggers.
  • Q: How do you prevent over-design? A: Structure the answer as constraints then tradeoffs: SLOs, capacity assumptions, bottlenecks, failure modes, and mitigation plans with clear triggers.
  • Q: Which constraints change architecture the most? A: Structure the answer as constraints then tradeoffs: SLOs, capacity assumptions, bottlenecks, failure modes, and mitigation plans with clear triggers.

Production Considerations

  • Align scope with team size and on-call maturity.
  • Document accepted risks explicitly.

Tradeoffs

  • Delivery speed vs architectural completeness.
  • Product breadth vs system depth.

Senior-Level Insights

  • Great answers show what you intentionally did not build.