Debugging a vLLM PagedAttention KV Cache Corruption Outage

Short summary

An on-call engineer describes a production outage caused by KV cache corruption in vLLM's PagedAttention during peak traffic at 14,720 RPS. After wasting 45 minutes on wrong fixes (timeout bumps, pod restarts, GPU health checks), the actual fix was a one-line Dockerfile change that is never shown. The team added Grafana alerts for NCCL errors and all_reduce latency to catch similar issues earlier.

• •vLLM PagedAttention KV cache corruption caused a production outage at 14,720 peak RPS
• •Three failed debugging attempts (timeouts, pod restarts, GPU checks) before finding a one-line Dockerfile fix that is not disclosed
• •Added Grafana alerts for NCCL errors and all_reduce latency to prevent future silent failures

Generated with AI, which can make mistakes.