On 2026-09-07 06:05:21Z k3s-prod-1 went NotReady ("Kubelet stopped posting node
status") with the host up, pingable and SSH-able. The cause was disk I/O
starvation of the embedded etcd, from its own journal:
slow fdatasync took=3.56s / 6.71s / 4.95s / 3.40s (expects 1s)
apply request took too long took=8.30s (expects 100ms)
etcdserver: too many requests
/proc/pressure/io FULL avg300 read 11.36 on k3s-prod-1 against 0.75 on
k3s-prod-2 (NVMe) and 1.29 on k3s-prod-3 — all three nodes put /data/k3s
(etcd's WAL) and /data/longhorn (every replica) on ONE partition, and node 1's
is a 2011 consumer SATA SSD with 61,440 reallocated sectors.
The stack alerted on CPU-PSI and memory and had NO I/O alert at all, so the
first signal the operator got was a node already out of the cluster. Adds:
NodeIOPressureHigh full IO PSI > 5% for 10m warning
NodeIOPressureCritical full IO PSI > 10% for 5m critical
Thresholds are measured, not guessed: rate() is a 0-1 fraction, so the outage's
11.36% is 0.1136 and the healthy steady state on the same node is ~0.01.
Verified live that node-exporter already exports
node_pressure_io_{stalled,waiting}_seconds_total for all three prod nodes, so
these rules fire on arrival — no new exporter, no scrape change. (etcd's own
fsync histograms are NOT available: kube-prometheus-stack's kubeEtcd scrape job
is deliberately disabled for k3s, so PSI is the signal we actually have.)
PSI *full* (every runnable task blocked on disk), not *some*: `some` is noisy on
a storage node and did not separate the failing node from its peers.
Dashboard gains the matching I/O row and is retitled accordingly. Not scoped to
prod — dev shares this file and its k3s VMs are HDD-backed, where the same alert
is if anything more likely to earn its keep.
Co-Authored-By: Claude Opus 5 <[email protected]>
(cherry picked from commit cb28fc80e7e2085d2539530d55f90fc92e3b1bba)
Adds NodeCPUPressureHigh (CPU PSI 'some' > 15% for 15m) and NodeCPULoadHigh (load5/core > 1 for 15m)
to platform-health.nodes, plus a 'Nodes — CPU / Memory Pressure' Grafana dashboard (PSI + load-per-core
+ utilization). These surface the bursty CPU contention that averaged CPU%/kubectl top hides — the
signal behind 'spikes cause blips of delay'. Makes the 6->8 vCPU resize measurable.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
jakman85
