GitHub outage: autoscaling policy missed Istio sidecar saturation

GitHub, autoscaling, and the component substitution fallacy

GitHub's recent outage was partly caused by an autoscaling policy that watched the host service but not the Istio sidecar's concurrency limits, leading to saturation. The post argues that focusing solely on fixing defective components, a fallacy identified by David Woods, misses how interactions between factors like traffic patterns, retry logic, and node saturation contributed. It urges treating interactions as first-class and investigating internal incident details beyond public writeups.