fix(longhorn): reduce guaranteed-instance-manager-cpu 12% → 6%#1665
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fix(longhorn): reduce guaranteed-instance-manager-cpu 12% → 6%#1665devantler wants to merge 1 commit into
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Live measurement of prod (2026-05-29): 6 Longhorn instance-managers each reserve ~474m (12% of a cx33) while using 8-30m -- ~2.7 cores locked, and instance-managers are not VPA-managed. Dropping the guarantee to 6% (~240m) keeps 8-16x headroom over observed usage and frees ~1.4 cores, while leaving margin for replica-rebuild CPU spikes. HOLD: applying this restarts the Longhorn data plane (instance-managers). Do not merge until the 4th worker is restored and Longhorn has replica-rebuild headroom -- the cluster is currently at 3 workers with replica count 3 (no N+1) following the worker-2 incident. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Pull request overview
This PR adjusts Longhorn’s HelmRelease default settings for Hetzner to reduce the CPU guaranteed (reserved) per Longhorn instance-manager, based on observed production usage, with the goal of freeing up schedulable CPU capacity on worker nodes.
Changes:
- Reduce
defaultSettings.guaranteedInstanceManagerCPUfrom the Longhorn default (12%) to 6% for both v1 and v2 instance-managers. - Add inline rationale documenting the measured production usage and the expected reclaimed CPU headroom.
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Summary
From a live per-container measurement of prod (2026-05-29, read-only): 6 Longhorn
instance-managerpods each reserve ~474m (12% of a cx33) while using 8–30m — ~2.7 cores locked, and instance-managers are not VPA-managed (so the auto-vpa policy can't right-size them).Change
guaranteedInstanceManagerCPU12% → 6% in the Longhorn HRdefaultSettings(v1 + v2). 6% ≈ 240m on a cx33 — still 8–16× headroom over observed usage — and frees ~1.4 cores, while leaving margin for the CPU spikes during Longhorn replica rebuilds.Why a separate, held PR
The companion right-sizing change (#1662) is GitOps-safe to land anytime. This one is not: changing the guaranteed CPU restarts instance-managers (the volume data plane). It must wait until the cluster is back to 4 workers and stable.
Validation
kubectl kustomize k8s/clusters/prod/builds. (Helm values aren't rendered by Kustomize; theguaranteedInstanceManagerCPUv1/v2 map form matches the 1.11.2 chart'slonghorn.multiTypeSettinghelper.)🤖 Generated with Claude Code