System Design Cases
Incident Management
Incident management concept (SRE): adapted ICS for software incidents. Severity levels (SEV1/2/3), Incident Commander (IC) coordinator role separate from Operations who fixes, Communications Lead handling status page, Scribe capturing timeline, SMEs on-demand. Detection via Prometheus SLO burn -> Alertmanager -> PagerDuty -> on-call IC. War room via Slack channel + Zoom + Incident.io orchestration. Customer comms via Statuspage (Investigating -> Identified -> Monitoring -> Resolved cadence every 30min) + Twitter + support macros. Mitigation toolkit: rollback, feature flag off, regional failover, manual circuit break — mitigate first, investigate later. Four scenarios: SEV-1 textbook response with rollback in 28min, statuspage 30-min comms cadence, follow-the-sun handoff between US and EU regions, anti-pattern of investigation > mitigation causing 45-min downtime. Includes 2 ADRs: rotating IC vs dedicated IC team, blameless culture enforcement.
Incident management: command, operations, communication, planning, and handoff
Incident management creates a temporary command structure for uncertain, time-sensitive work. Google SRE separates command, operations, communications, and planning. The incident commander coordinates objectives and priorities; Operations changes the system; Communications maintains stakeholder updates; Planning tracks future work and handoffs. Smaller incidents may combine roles deliberately, but responsibilities must remain explicit.
Mitigation restores acceptable service and can precede root-cause analysis, yet it is not “act without evidence.” Changes remain scoped, reviewed when feasible, logged, reversible, and verified against user impact. A live incident document records times, decisions, owners and evidence so that status and later learning do not depend on memory.
Модель и предпосылки
- Example timeline is internally consistent: detect 12 UTC, declare 12, choose rollback 12, complete mitigation 12, verify through 12, resolve 12.
- External updates follow a declared cadence and contain impact, scope, current action and next-update time without asserting an unverified root cause.
- A handoff is acknowledged by the receiving commander/operations lead and transfers current status, outstanding risks, permissions and next checkpoints; “follow the sun” does not guarantee nobody works at night.
Проверяемые утверждения
- C1. Incident response benefits from explicit command, operations, communications and planning responsibilities plus a shared incident state.
- C2. The incident commander coordinates rather than becoming the default system operator; role combinations are explicit when staffing is small.
- C3. Communications provide accurate, regular updates and avoid speculation about root cause while investigation is incomplete.
- C4. Handoffs require an explicit transfer and acknowledgement rather than an assumed timezone boundary; multi-site operation has coordination trade-offs even when it reduces night shifts.
- C5. Incident preparation, detection, response and recovery are part of a broader risk-management lifecycle.
Исполняемые сценарии
Detect, declare, and assign roles. At 12
monitoring detects impact; at 12 the commander declares the incident and assigns explicit responsibilities.Mitigate and verify. Operations chooses rollback at 12
, completes it at 12, and resolves only after user-level verification at 12.Evidence-based customer communication. Communications reports confirmed impact, mitigation and the next update without speculating about root cause.
Acknowledged handoff. The outgoing planning lead transfers current state and receives explicit acknowledgement from the next shift.
Ошибки проектирования
- Не назначайте IC одновременно главным оператором без явного решения о совмещении ролей.
- Не публикуйте root cause во время mitigation как установленный факт.
- Не объявляйте resolved до user-level verification и фиксации residual risk.
- Не обещайте фиксированный MTTR multiplier или универсальные SEV deadlines без собственной статистики/договора.
Границы гарантии
- Severity definitions, update cadence and escalation timers are organization-specific.
- Security, privacy, safety and regulatory incidents can require specialized command and notification paths.
- Timeline timestamps are observations with sources; clock correction and late evidence must remain auditable.