| Identified misleading symptom |
Recognized low kubectl top CPU with high process CPU usage as throttling; checked cpu.stat |
Noticed the CPU numbers did not add up but took time to find the throttle metrics |
Investigated SMTP, database, or application code for the bottleneck |
| Found root cause in kubernetes domain |
Identified CFS throttling from CPU limits on multi-threaded workload |
Found the CPU limit was too low but not why it worked before the kernel upgrade |
Assumed the workers needed more replicas or the queue had a consumer bug |
| Remediated in linux_ops domain |
Adjusted CFS bandwidth slice sysctl on all nodes; updated CPU limits; applied via Ansible |
Increased CPU limits but did not fix the kernel-level sysctl |
Only increased replicas (scaling around the problem, not fixing it) |
| Cross-domain thinking |
Explained the full chain: kernel upgrade -> CFS behavior change -> throttling -> worker slowdown -> queue backlog |
Acknowledged throttling but missed the kernel upgrade connection |
Treated it as an application performance or capacity planning issue |