A postmortem that assigns blame fixes nothing. Here is the blameless postmortem template that senior SREs actually use to find root causes and prevent recurrence.
Focus the Five Whys on why your system had no resilience against the vendor failure, not on the vendor itself. Questions like 'why did we have no circuit breaker?' or 'why was the vendor SLA not reflected in our own SLO budget?' surface actionable internal improvements. Vendor postmortems are their responsibility — yours is hardening your dependency architecture.
Track two metrics quarterly: repeat incident rate by root cause category (config error, dependency failure, capacity) and mean time between same-category incidents. If the same root cause category appears more than once in six months despite action items being closed, the action items addressed symptoms rather than the systemic cause. Use this signal to reopen the postmortem and re-examine the Five Whys depth.
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