# longhorn-degraded — A Longhorn volume has been degraded for 10 minutes **Alert:** `LonghornVolumeDegraded` (warning, 10m) **File:** `platform/monitoring/alerts.yaml`, group `platform-health.longhorn` **Expression:** `longhorn_volume_robustness == 2` (0=unknown 1=healthy 2=degraded 3=faulted) ## What this means here A volume has fewer healthy replicas than it should. It is **still serving I/O** — that is the difference between degraded and faulted (`/runbooks/longhorn-faulted`). What you have lost is redundancy, and on a 3-node cluster with hard node anti-affinity (`replicaSoftAntiAffinity: false`, `numberOfReplicas: 3`) one degraded volume means one more node loss away from data loss. **Degraded is the NORMAL state after any node reboot on this cluster, and it is expensive.** Recorded plainly in the stabilization notes: *"Longhorn on the HDD: every node reboot degrades all 18 volumes → full rebuild (slow; 30%+ IO-delay). Roll reboots one node at a time; wait `robustness=healthy` before the next."* The rebuild is the thing that hurts, not the degradation: rebuild writes land on the same partition as the embedded etcd WAL (`/data/k3s` and `/data/longhorn` share one device), and that is the mechanism behind the 2026-09-07 `k3s-prod-1` NotReady outage. So the question to answer is never just "why is it degraded" but "is the rebuild about to take a node out". Cross-read `/runbooks/node-io`. ### Verify the alert can even fire (measured 2026-09-13) Prometheus on prod scrapes 19 jobs: `apiserver`, `cdi-prometheus-metrics`, `coredns`, `keycloak-discovery`, `keycloak-service`, `keycloak/keycloak-db`, `kube-prometheus-stack-alertmanager`, `kube-prometheus-stack-grafana`, `kube-prometheus-stack-operator`, `kube-prometheus-stack-prometheus`, `kube-state-metrics`, `kubelet`, `kubevirt-prometheus-metrics`, `nextcloud-db/nextcloud-db`, `node-exporter`, `oauth2-proxy`, `semaphore-db/semaphore-db`, `velero`, `velero/node-agent`. There is **no** Longhorn, cert-manager, Flux-controller or Hubble/Cilium job. Check the series this rule depends on before you trust its silence: ``` infra/devcontainer/dev.sh run bash -c \ 'kubectl --context k3s-prod -n monitoring port-forward svc/kube-prometheus-stack-prometheus 19090:9090 & \ sleep 5; curl -s -G --data-urlencode "query=count by (job) (up)" localhost:19090/api/v1/query' ``` **This alert is currently INERT.** `count(longhorn_volume_robustness)` returned **0 series** on prod on 2026-09-13: the whole `platform-health.longhorn` rule group has no data, because Longhorn ships no ServiceMonitor here. That is a separate open defect, and the practical consequence is that **you will probably learn about a degraded volume from an application symptom or from `volumes.longhorn.io`, not from this alert**. Do not infer "no alert, so volumes are fine". ## Running the commands in this runbook `kubectl` does not work on the operator workstation. The toolchain lives only in the pinned dev container, and the host's `k3s-oidc` context hangs on a browser prompt once its token expires — that hang is not the cluster being down. Every command below runs as: infra/devcontainer/dev.sh run bash -c 'kubectl --context k3s-prod get nodes' Always pass `--context k3s-prod` explicitly. `dev.sh` merges BOTH clusters into one kubeconfig and picks a current-context per invocation, and **that default has already changed once** — it was k3s-dev until dev was decommissioned on 2026-09-13, and is k3s-prod now. A command that names its context means the same thing next month as it does today; one that relies on the default does not, and the failure is silent (it answers confidently about the other cluster). `CLUSTER=prod infra/devcontainer/dev.sh run kubectl ...` selects it explicitly, and every invocation prints a banner naming the cluster it is about to talk to — read it. Do not run two `dev.sh` invocations at once; they share one container and interfere. USE FULLY-QUALIFIED RESOURCE NAMES, ALWAYS. Three CRDs on this cluster register the kind `Backup`: `longhorn.io/v1beta2`, `postgresql.cnpg.io/v1` and `velero.io/v1`. The bare short name resolves to Longhorn's, which holds zero objects — so `kubectl get backup -A` prints **"No resources found"** on a cluster holding 6 Velero backups and 27 CNPG backups. Verified on prod 2026-09-13. Reading that as "the backups are gone" and acting on it turns a false negative into real data loss. Write `backups.velero.io`, `backups.postgresql.cnpg.io`, `clusters.postgresql.cnpg.io`, `settings.longhorn.io`, `volumes.longhorn.io`, `nodes.longhorn.io`. Mutating kubectl (`apply`, `patch`, `annotate`, `rollout`) and `flux reconcile` are blocked for agents here: every durable change goes through git (`git push origin main` **is** the deploy). Where this runbook gives a mutating command it is for an operator, and it says so. ## First commands The truth about robustness, straight from the CRs (this works whether or not the metric does): ``` infra/devcontainer/dev.sh run bash -c \ 'kubectl --context k3s-prod -n longhorn-system get volumes.longhorn.io \ -o custom-columns=NAME:.metadata.name,ROBUST:.status.robustness,STATE:.status.state,NODE:.status.currentNodeID,SIZE:.spec.size' ``` Which replicas are missing, and where: ``` infra/devcontainer/dev.sh run bash -c \ 'kubectl --context k3s-prod -n longhorn-system get replicas.longhorn.io \ -o custom-columns=NAME:.metadata.name,VOL:.spec.volumeName,NODE:.spec.nodeID,RUNNING:.status.currentState | sort -k2' ``` Which PVC/workload is affected: ``` infra/devcontainer/dev.sh run bash -c \ 'kubectl --context k3s-prod get pv -o custom-columns=PV:.metadata.name,CLAIM:.spec.claimRef.namespace/.spec.claimRef.name,SC:.spec.storageClassName' ``` Are the nodes and their disks schedulable, and is a rebuild in flight? ``` infra/devcontainer/dev.sh run bash -c \ 'kubectl --context k3s-prod -n longhorn-system get nodes.longhorn.io -o wide; echo; \ kubectl --context k3s-prod -n longhorn-system get settings.longhorn.io concurrent-replica-rebuild-per-node-limit -o custom-columns=NAME:.metadata.name,VALUE:.value' ``` And the pressure that rebuild is causing — the reason this alert matters: ``` ssh k3s-prod-1 'cat /proc/pressure/io' ``` ## Likely causes, most likely first ### 1. A node rebooted or was briefly NotReady (overwhelmingly the most common) Expected, and it self-heals by rebuilding. Your job is to keep the rebuild from taking a node down. Remediation (operator, mutating) — freeze rebuilds while replicas will **reattach** (an in-place bounce): ``` infra/devcontainer/dev.sh run bash -c \ 'kubectl --context k3s-prod -n longhorn-system patch settings.longhorn.io \ concurrent-replica-rebuild-per-node-limit --type=merge -p "{\"value\":\"0\"}"' ``` Thaw to `"1"` — never higher — once every volume reads `healthy`. Use `1` rather than `0` when the replicas are genuinely gone (an OS re-provision), so replenishment can actually proceed. `concurrentReplicaRebuildPerNodeLimit: 1` was **already in force during the 2026-09-07 outage and held**; do not "fix" this by setting a knob that is already set. `replicaRebuildingBandwidthLimit` is **v2/SPDK-only** and does nothing here; `rebuildConcurrentSyncLimit` is already at its floor of 1. What was actually tightened after that incident was every *other* Longhorn I/O source: `concurrentVolumeBackupRestorePerNodeLimit` and `snapshotHeavyTaskConcurrentLimit` 5 → 1. ### 2. A node is still down Then the rebuild cannot complete and this will not clear. Go to `/runbooks/node-down` first; there is nothing to fix in Longhorn. ### 3. A disk was replaced and Longhorn refuses it Signature: `DiskFilesystemChanged` — *"record diskUUID doesn't match the one on the disk"*. Remediation, in exactly this order (the validating webhook enforces it): **disable the disk → remove the disk entry → re-add it**. Seen during the 2026-09-07 drive swap. ### 4. No node can hold the replica (anti-affinity or space) Hard anti-affinity means a 3-replica volume needs three distinct schedulable nodes. With one node cordoned or its disk over `storageMinimalAvailablePercentage: 25`, the third replica cannot be placed and the volume stays degraded indefinitely. Check `nodes.longhorn.io` scheduling and `/runbooks/longhorn-capacity`. ### 5. `replicaAutoBalance: best-effort` is shuffling replicas Normal background behaviour, transient. If degradation follows a pattern of replicas moving and never settling, that is worth an operator's attention. ## When to escalate or stop - **If more than one volume is degraded and I/O-PSI on any node is climbing, freeze rebuilds first and then get the operator.** That combination is the 2026-09-07 failure mode in progress. - **Never reboot, cordon or re-provision a second node while any volume is degraded.** This is the single most important rule in this runbook. - **Do not `kubectl drain`.** This cluster deliberately does not drain: there is no Longhorn `nodeDrainPolicy` configured anywhere in the repo, the upgrade plan rejects system-upgrade-controller because "its auto-drain fights this cluster's slow-HDD Longhorn", and the node-loss conformance test evicts only its own writer pod. - **Do not delete a degraded volume's replicas to "force a clean rebuild"** unless the operator agrees — with 3 replicas and one already missing you are one mistake from `/runbooks/longhorn-faulted`. - Escalate for: a node that will not come back, a disk replacement, or a volume degraded for more than a few hours with all three nodes Ready (that is a Longhorn bug, not an operational state). --- Source of truth: `runbooks/longhorn-degraded.md`. Index: `/runbooks/` Records: `DECISIONS-LOG.md` "2026-08-31 — Post-upgrade stabilization" (the reboot tax) and "2026-09-07 — k3s-prod-1 NotReady"; `docs/plans/cluster-upgrade-plan.md` §6.2/§7 (the freeze/thaw).