Kubernetes App Slowness Traced to Redis Queue Blocking, Not Infrastructure

A developer deploying a voting app on AWS EKS via Terraform and Kubernetes noticed intermittent response times ranging from under a second to 60 seconds, despite all pods showing healthy. Initial suspects like AWS Classic ELB warm-up and DNS propagation were ruled out using curl's timing breakdown, which showed TCP connections completing in under 40ms every time. Further testing across three pod replicas revealed the same pod could respond instantly or take nearly a minute, eliminating the theory of a single faulty pod or node. Since all voting pods shared one Redis instance, Redis was inspected next, showing sub-millisecond average command latency. However, the investigation pointed toward Redis's single-threaded command queue as a potential bottleneck, where bursts of commands could cause delays even when individual commands were fast.