4Non-functional design

• 4.1Performance design and capacity planning

  Covers the distinction between response time, which drives user experience, and throughput, which measures processing capacity; the utilization (ρ)-to-wait-time relationship under the basic M/M/1 queueing model; and the judgment to diagnose bottlenecks and size capacity, built through business-requirement scenarios.

• 4.2Reliability design

  Covers the five RASIS metrics for measuring system reliability, availability calculation for series/parallel configurations, and the distinctions among fault tolerant, fail-soft, and fail-safe behavior under failure, learned through cost-versus-reliability tradeoff judgments.

• 4.3Availability and disaster preparedness

  Covers judging which redundant configuration to choose from a target availability, the HA cluster, which makes multiple servers behave as one system, DR (disaster recovery) and BCP (business continuity plan) for large-scale disasters, and RTO (recovery time objective)/RPO (recovery point objective), which quantify recovery targets.

• 4.4Security architecture

  Covers defense in depth, which compensates for the limits of perimeter defense; the zero trust mindset, which trusts nothing by default even internally; the distinction between authentication (verifying identity) and authorization (determining permissions); and secure by design, which builds security in from the earliest design stage, along with threat analysis, learned through architecture judgments tailored to business requirements.