Measurement

Uptime/downtime definition; the nines table (90%–99.999%); techniques for high availability; dependency chaining effects; design-for-production philosophy; ROI of availability investment; MTBF/MTTR/RPO/RTO measurement framework; tyranny of the nines antipattern; Allspaw: MTTR > MTBF; SRE: 100% is always the wrong target

GQM framework (Basili & Weiss 1984): goal → questions → metrics → data tree; goal statement structure (purpose/object/issue/viewpoint); metric selection criteria (signal strength, cost, cross-question reuse); 9-step workshop; Foo Service case study (rate-limit incident → heartbeat + fail-fast ADR → 10-minute detection before user impact)