Postmortem: The 2026 Slack Outage Due to Istio 1.22 Circuit Breaker Misconfiguration

Postmortem: The 2026 Slack Outage Due to Istio 1.22 Circuit Breaker Misconfiguration Executive Summary On March 12, 2026, Slack experienced a global outage lasting 2 hours and 27 minutes, rendering core messaging and collaboration features unavailable to 18.2 million active users. The incident was traced to a misconfiguration in Istio 1.22's circuit breaker (outlier detection) settings for the chat-api service, which triggered mass ejection of healthy backend pods. This postmortem details the in