The Curious Case of the Phantom Instance

This post details the investigation and resolution of a 'phantom instance' issue observed in ELB health check metrics. The root cause was identified as the coexistence of old and new ELB nodes during ELB scaling events, which temporarily doubled health check counts. This led to a refinement in monitoring practices to distinguish between ELB health checks and dependency health checks, and to account for multiple ELBs serving the same cluster.