feat(monitoring): scrape Longhorn + cert-manager — 8 alerts were structurally inert

An alert rule whose metric is never scraped is not a broken alert, it is an ABSENT
alert that reads as a present one. `longhorn_volume_robustness == 2` over a TSDB
with no longhorn_* series returns no vector: permanently quiet, permanently
"healthy", indistinguishable from a correct rule. It survives review (the PromQL is
right), it survives `promtool test rules` (the unit test supplies the series
itself), and it appears on no dashboard.

VERIFIED ABSENT ON PROD before this change (re-verified 2026-09-13 21:0xZ, ~15h
after the first audit, because a stale reading is not evidence):

  count(longhorn_volume_robustness)                      => (empty)   4 rules inert
  count({__name__=~"certmanager.*"})                     => (empty)   3 rules inert
  count(hubble_drop_total) / {__name__=~"cilium.*"}      => (empty)   1 rule inert
  count by (job) (up)                                    => 20 jobs, none of them
                                                            Longhorn, cert-manager,
                                                            Cilium or Hubble

Consequence: storage health was unmonitored on the cluster whose prod-1 had just
had a failing SSD, and TLS expiry was unmonitored with the live `wildcard-home`
wildcard 89 days from expiry on an ACME DNS-01 renewal that can fail silently.

WHAT THIS CHANGES

  * platform/longhorn: `metrics.serviceMonitor.enabled: true` (the supported chart
    way — rendering longhorn 1.12.1 emits exactly 1 ServiceMonitor with the flag and
    0 without), plus networkpolicy-metrics.yaml. The NetworkPolicy is LOAD-BEARING,
    not belt-and-braces: measured with the monitor applied and no allowance, all 3
    targets were DISCOVERED and every scrape failed `context deadline exceeded`
    after 10.0s — a drop, not a refusal — while curling the endpoint from inside
    the manager pod returned 200 in 0.031s. Longhorn 1.12.1 ships 6 NetworkPolicies
    of its own, guarded on `networkPolicies.restrictInternalTraffic` (default TRUE)
    and NOT on `networkPolicies.enabled`, so they are effectively unconditional and
    the manager policy admits only same-namespace Longhorn components. The one-line
    alternative (restrictInternalTraffic: false) was rejected: it deletes the
    internal-traffic restriction across all six components to open one port to one
    namespace, trading an R-SEC-02 control for an observability one when the two do
    not conflict. This policy is Ingress-only, ns monitoring -> app=longhorn-manager,
    TCP 9500 only; 9502/9503 (webhook, recovery backend) stay closed.

  * platform/cert-manager: `prometheus.servicemonitor.enabled: true`. Chart default
    already serves 9402; only the monitor was missing. No NetworkPolicy needed —
    neither ns cert-manager nor ns monitoring carries one. NOT paired with
    prometheus.podmonitor.enabled: the chart calls `fail` if both are set.

  * platform/kubevirt: KubeVirtVMLaunchFailing queried
    `kubevirt_vmi_phase_count{phase="Failed"}`, which DOES NOT EXIST on the deployed
    KubeVirt — a different flavour of the same defect, with the scrape target up and
    healthy. Prod has only `kubevirt_vmi_info` and `kubevirt_vmi_number_of_outdated`;
    the only phase-bearing names are the phase_transition_time histograms. Corrected
    to `kubevirt_vmi_info{phase="failed"}` — LOWERCASE, because KubeVirt lowercases
    the value (observed `phase="running"` for the unifi VMI) and a capital-F matcher
    would select nothing and be exactly as inert.

PROVEN, NOT ASSERTED. The rendered ServiceMonitors were applied to prod by hand and
the metrics observed to land, then REMOVED again so the merge's Helm upgrade creates
and owns them rather than colliding with an unowned object:

  count(up{job="longhorn-backend"})        => 3        (all three managers, up==1)
  count({__name__=~"longhorn.*"})          => 8717     (was empty)
  count(longhorn_volume_robustness)        => 44
  up{namespace="cert-manager"}             => 3 targets, all 1
  count({__name__=~"certmanager.*"})       => 104      (was empty)
  wildcard-home days to expiry             => 89.2, ready_status{condition="True"}=1

All 58 alert rules in the repo were then evaluated against prod one by one: every
one returns a result without error, and exactly ONE fires.

TRIAGE OF THE ONE NEWLY-FIRING ALERT — A TRUE POSITIVE, NOT TUNED AWAY.
LonghornVolumeCapacityHigh on the Prometheus TSDB volume:
`longhorn_volume_actual_size_bytes / longhorn_volume_capacity_bytes` = 0.971
(48.6 GiB allocated of 50 GiB) while the kubelet's view of the same filesystem is
only 20.4% used. Longhorn is not reclaiming freed blocks, so ~48.6 GiB x 3 replicas
is committed for ~10 GiB of real data. On a cluster whose failure mode is disk
pressure and whose etcd WAL shares a spindle with Longhorn, that is worth knowing
and was invisible until now. The threshold is left alone; the follow-up is
filesystem trim, not a bigger number.

THE GUARD (conformance/tests/l0-static/alert-metrics-have-scrape-targets)

Whole-repo L0 invariant, 118 assertions. It crosses from each alert to the scrape
config that makes its metric exist: every metric name is claimed by exactly one
declared owner, and each owner's enabling declaration is re-proven against the
working tree on every gate run, including the negative conditions that defeat an
enablement without deleting it. `up{job="X"}` is audited on its own axis, because
`up` always exists: where this repo authors a Service and a ServiceMonitor in the
same file, the monitor's endpoint port must be a port that Service defines.

It DECLARES conformance.home.k3s/scope: "whole-repo" and adds NO ci/l0.sh stage —
the whole-repo-invariants-wired meta-test fails the gate if one reappears.

PROVEN ABLE TO FAIL, five ways, each reverted:
  1. an alert on a fabricated metric          -> FAIL "claimed by NO entry"
  2. longhorn metrics.serviceMonitor removed  -> FAIL "no longer matches"
  3. networkpolicy-metrics.yaml unwired       -> FAIL "the monitor alone is NOT enough"
  4. cert-manager podmonitor also enabled     -> FAIL "FORBIDDEN pattern"
  5. a register entry made stale / removed    -> FAIL in both directions

TWO SHRINK-ONLY REGISTERS, because a blanket fail would make the gate red until
work that is not this change lands, and a disabled gate protects nothing:

  * KNOWN_UNWIRED_METRICS (1): hubble_drop_total. See below.
  * KNOWN_UNWIRED_JOBS (12): every apps/* `<app>-down` SLI rule is ALSO inert, and
    this was found by the re-audit, not previously known. The rendered
    ServiceMonitors name `port: metrics` and NOT ONE of the twelve app Services
    defines a port of that name (zero occurrences of `name: metrics` across all
    twelve manifests); prod confirms none of the twelve jobs appears in `up`. This
    is the nastiest variant of the class: `up` exists in abundance so nothing looks
    wrong, and PrometheusTargetsMissing cannot see it either, because a target that
    was never discovered has no up series to be 0. Closing it needs an exporter per
    app (Plex, Pi-hole, Jackett, qBittorrent, Sonarr, Radarr, Seerr speak no
    Prometheus) — except keycloak, where the live jobs are keycloak-service /
    keycloak-discovery and the rule is a rename away from being live.

NOT DONE HERE, DELIBERATELY: Hubble. hubble.metrics.enabled RECONFIGURES THE CNI —
it opens 9965 on every cilium-agent and rolls the DaemonSet across all three nodes,
serialised by this repo's own maxUnavailable: 1 (set after the 2026-09-01
k8sServiceHost outage, where a CNI roll deadlocked 2 of 3 agents). It also needs a
matching edit to roles/cilium/templates/cilium-values.yaml.j2 in the same commit,
because platform/cilium/helmrelease.yaml carries a [parity] contract against it and
a rebuilt node would otherwise bootstrap a CNI config that disagrees with the
reconciled one. Recommended as its own change on the cilium Kustomization, with the
Ansible parity edit, a narrow labelsContext, and a one-node canary — not smuggled in
here.

ALSO FOUND, NOT FIXED HERE: kube-state-metrics is OOMKilled every ~10 minutes on
prod (90 restarts in 16h against a 128Mi limit) while its logs show the
custom-resource-state factory reloading every 3 seconds. Thirteen alert rules read
kube_* metrics, so those rules are INTERMITTENTLY inert — the same defect class,
arriving through a crashloop rather than a missing monitor. Needs its own change.

Co-Authored-By: Claude Opus 5 <[email protected]>

platform/cert-manager/helmrelease.yaml

@@ -31,3 +31,53 @@ spec:
     # cluster/split-horizon DNS (docs/09 split-horizon note; realises the TODO that was here).
     dns01RecursiveNameservers: "1.1.1.1:53,8.8.8.8:53"
     dns01RecursiveNameserversOnly: true
+    # --- SCRAPE THE TLS ISSUER, or every certificate alert is INERT (added 2026-09-13) ----------
+    # platform/monitoring/alerts.yaml ships CertificateExpiringSoon, CertificateExpiryImminent
+    # (critical) and CertificateNotReady — and NONE of them could ever fire. The chart exposes the
+    # controller's metrics port by default (`prometheus.enabled: true`, confirmed on prod:
+    # Service/cert-manager listens on 9402) but defaults `prometheus.servicemonitor.enabled: false`,
+    # and no ServiceMonitor existed in ns cert-manager. VERIFIED live on prod 2026-09-13:
+    # `count({__name__=~"certmanager.*"})` returned NOTHING and `count by (job) (up)` listed no
+    # cert-manager job — so certmanager_certificate_expiration_timestamp_seconds and
+    # certmanager_certificate_ready_status were never in the TSDB.
+    #
+    # WHY THIS IS PART OF THE TLS PATH: the live wildcard `wildcard-home` (ns gateway) expires
+    # 2026-12-12T02:16:57Z and is renewed by an ACME DNS-01 order that can fail quietly — a Cloudflare
+    # token rotation, a DNS-01 self-check timeout (the very failure the two lines above work around),
+    # a rate limit. With no scrape, the FIRST signal of a failed renewal is a browser TLS error for
+    # every *.${BASE_DOMAIN} service. That is a user-discovered outage on a fully automated path,
+    # which is exactly what R-TLS-01/R-OBS-04 exist to prevent.
+    #
+    # Chart mechanics, verified by rendering cert-manager v1.21.2 (the version this range resolves to):
+    #   * templates/servicemonitor.yaml renders on `prometheus.enabled AND
+    #     prometheus.servicemonitor.enabled`. Measured: `helm template --set
+    #     prometheus.servicemonitor.enabled=true` emits exactly 1 ServiceMonitor, 0 without it.
+    #     `prometheus.enabled` is already true by chart default, so this one line is sufficient.
+    #   * podmonitor and servicemonitor are MUTUALLY EXCLUSIVE — the chart calls `fail` if both are
+    #     set. Do not add `prometheus.podmonitor.enabled` alongside this.
+    #   * the rendered ServiceMonitor selects the controller/webhook/cainjector Services by
+    #     app.kubernetes.io/{name,instance,component} on targetPort `http-metrics`, and sets
+    #     `jobLabel: app.kubernetes.io/name` — so the scrape job lands as `cert-manager`.
+    #   * it carries the label `prometheus: default` (servicemonitor.prometheusInstance). Harmless
+    #     here: platform/monitoring sets serviceMonitorSelectorNilUsesHelmValues false, so Prometheus
+    #     selects every ServiceMonitor regardless of labels. Left at the chart default deliberately —
+    #     overriding it would imply a label-selecting Prometheus this cluster does not have.
+    # Cost: 3 scrape targets, one certmanager_* series set — negligible.
+    #
+    # PROVEN END TO END ON PROD, 2026-09-13 21:0xZ, by applying the rendered ServiceMonitor by hand
+    # (then removing it, so the merge's Helm upgrade owns it) — no NetworkPolicy was needed, as
+    # neither ns cert-manager nor ns monitoring carries one:
+    #   up{namespace="cert-manager"}                  => 3 targets, all 1
+    #                                                    (jobs cert-manager / cainjector / webhook,
+    #                                                     because jobLabel is app.kubernetes.io/name)
+    #   count({__name__=~"certmanager.*"})            => 104    (was EMPTY)
+    #   (certmanager_certificate_expiration_timestamp_seconds - time())/86400
+    #                                                 => 89.2 days for `wildcard-home` (ns gateway,
+    #                                                    ClusterIssuer letsencrypt-prod)
+    #   certmanager_certificate_ready_status{condition="True"} => 1
+    # So the three Certificate* rules now evaluate against a real series and are correctly QUIET:
+    # the wildcard is healthy and 89 days out, which is exactly what CertificateExpiringSoon's 14-day
+    # threshold is meant to catch and could not have.
+    prometheus:
+      servicemonitor:
+        enabled: true

platform/cert-manager/values.yaml

@@ -4,3 +4,8 @@
 # dns01RecursiveNameservers / -Only           # TODO(WS-SEC): may be needed with split-horizon DNS
 # ClusterIssuers (letsencrypt-staging/-prod) live in clusterissuers.yaml, not here.
 # Cloudflare API token: SOPS-encrypted secret `cloudflare-api-token` (WS-SEC, OQ-4) — name only.
+# prometheus.servicemonitor.enabled: true     # scrape the controller's 9402 metrics port; without it
+#                                             # the certmanager_* family is absent from the TSDB and
+#                                             # the three Certificate* alert rules in
+#                                             # platform/monitoring/alerts.yaml are INERT. Mutually
+#                                             # exclusive with prometheus.podmonitor.enabled.