58789cde8b
Test 3 validation surfaced two latent bugs in the sentinel-gate DaemonSet that have been masked since 2026-04-18 (when uu was off, nothing wrote /var/run/reboot-required, so the gate never had to fire): 1. automount_service_account_token=false on both the SA and the pod spec → kubectl in the script falls back to localhost:8080 on every call. Each check (`kubectl get nodes`, `kubectl get pods -n calico-system`, transition-time read) errors to stderr and emits empty stdout. `wc -l` reports 0 → checks "pass" with no real data. 2. bitnami/kubectl:latest runs as uid=1001 by default. The hostPath /var/run is root:root 0755 → final `touch /host/var-run/gated-reboot-required` failed with EACCES. Fail-safe by accident — but if anything had ever loosened those perms, the broken checks above would have green-lit the gate with no real validation. Fix: enable token mount on the SA + pod, set securityContext.run_as_user=0 on the container. Verified post-fix: kubectl returns all 5 nodes, touch succeeds, sentinel-gate now reports the correct `BLOCKED: A node transitioned Ready within the last 24 hours (soak window)` when triggered with k8s-node1's recent reboot within the cool-down period. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
289 lines
11 KiB
HCL
289 lines
11 KiB
HCL
# kured — Kubernetes Reboot Daemon
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#
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# Auto-reboots nodes when /var/run/reboot-required exists on the host (set by
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# unattended-upgrades). The reboot process is gated by a custom sentinel file
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# (kured-sentinel-gate DaemonSet below) and by Prometheus alerts so reboots
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# only happen when:
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# - all nodes Ready
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# - all calico-node pods Running
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# - no node has transitioned Ready in the last 24 hours (24h soak)
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# - no Prometheus alert is firing (excluding self-referential ignore-list)
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#
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# History:
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# - 2026-03 post-mortem (memory 390): 26h cluster outage triggered by kured
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# rebooting nodes while containerd's overlayfs snapshotter was corrupted.
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# Remediation included the sentinel gate and a tight reboot window
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# (Mon-Fri 02:00-06:00 London).
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# - 2026-04-18: adopted into Terraform (Wave 5a). Previously helm-installed
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# manually + kubectl-applied sentinel gate.
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# - 2026-05-10: re-enabled unattended-upgrades (cloud_init.yaml flipped from
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# remove → install). Sentinel cool-down stretched 30m → 24h. Added Helm
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# values prometheusUrl + alertFilterRegexp so any non-ignored firing alert
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# halts the rollout. New "Upgrade Gates" alert group in monitoring stack
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# (KubeAPIServerDown, KubeStateMetricsDown, PrometheusRuleEvaluationFailing,
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# PVCStuckPending, RecentNodeReboot, MysqlStandaloneDown,
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# ClusterPodReadyRatioDropped, NodeMemoryPressure, NodeDiskPressure,
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# KubeQuotaAlmostFull) provides explicit cluster-health gating.
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resource "kubernetes_namespace" "kured" {
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metadata {
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name = "kured"
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labels = {
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"istio-injection" = "disabled"
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tier = local.tiers.cluster
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}
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}
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lifecycle {
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# KYVERNO_LIFECYCLE_V1: goldilocks-vpa-auto-mode ClusterPolicy stamps this label on every namespace
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ignore_changes = [metadata[0].labels["goldilocks.fairwinds.com/vpa-update-mode"]]
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}
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}
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# -----------------------------------------------------------------------------
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# kured Helm release
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# -----------------------------------------------------------------------------
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resource "helm_release" "kured" {
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namespace = kubernetes_namespace.kured.metadata[0].name
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create_namespace = false
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name = "kured"
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chart = "kured"
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repository = "https://kubereboot.github.io/charts/"
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version = "5.11.0"
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values = [yamlencode({
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configuration = {
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period = "1h0m0s"
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timeZone = "Europe/London"
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startTime = "02:00"
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endTime = "06:00"
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rebootDays = ["mo", "tu", "we", "th", "fr"]
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rebootSentinel = "/sentinel/gated-reboot-required"
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notifyUrl = data.vault_kv_secret_v2.secrets.data["slack_kured_webhook"]
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concurrency = 1
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rebootDelay = "30s"
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# Halt rolling reboots when ANY firing Prometheus alert is not in the
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# ignore-list. The ignore-list excludes self-referential / always-firing
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# alerts that would otherwise deadlock kured. alertFilterMatchOnly stays
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# false (default) so the regex marks alerts to IGNORE — every other
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# firing alert blocks. See "Upgrade Gates" group in monitoring stack.
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prometheusUrl = "http://prometheus-server.monitoring.svc.cluster.local:80"
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alertFilterRegexp = "^(Watchdog|RebootRequired|KuredNodeWasNotDrained|InfoInhibitor)$"
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alertFiringOnly = true
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alertFilterMatchOnly = false
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}
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reboot_days = "mon,tue,wed,thu,fri"
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window_end = "06:00"
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window_start = "22:00"
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service = {
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annotations = {
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"prometheus.io/scrape" = "true"
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"prometheus.io/port" = "8080"
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"prometheus.io/path" = "/metrics"
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}
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}
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})]
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}
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data "vault_kv_secret_v2" "secrets" {
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mount = "secret"
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name = "kured"
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}
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# -----------------------------------------------------------------------------
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# kured-sentinel-gate
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#
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# Runs a DaemonSet that creates /var/run/gated-reboot-required ONLY when all
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# safety preconditions are met (see script). kured's rebootSentinel points at
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# this file, so reboots are effectively blocked unless every check passes.
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# -----------------------------------------------------------------------------
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resource "kubernetes_service_account" "kured_sentinel_gate" {
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metadata {
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name = "kured-sentinel-gate"
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namespace = kubernetes_namespace.kured.metadata[0].name
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}
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# Token IS mounted — the script uses kubectl to read nodes + pods state for
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# the safety checks. Without an authenticated token, kubectl falls back to
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# localhost:8080 (no proxy in distroless-ish image), every check silently
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# no-ops on parse-empty stdout, and the gate appears to PASS when it
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# shouldn't. Mount the token. (Found 2026-05-10 during Test 3 validation.)
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automount_service_account_token = true
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}
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resource "kubernetes_cluster_role" "kured_sentinel_gate" {
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metadata {
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name = "kured-sentinel-gate"
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}
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rule {
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api_groups = [""]
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resources = ["nodes"]
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verbs = ["list"]
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}
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rule {
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api_groups = [""]
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resources = ["pods"]
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verbs = ["list"]
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}
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}
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resource "kubernetes_cluster_role_binding" "kured_sentinel_gate" {
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metadata {
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name = "kured-sentinel-gate"
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}
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role_ref {
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api_group = "rbac.authorization.k8s.io"
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kind = "ClusterRole"
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name = kubernetes_cluster_role.kured_sentinel_gate.metadata[0].name
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}
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subject {
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kind = "ServiceAccount"
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name = kubernetes_service_account.kured_sentinel_gate.metadata[0].name
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namespace = kubernetes_namespace.kured.metadata[0].name
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}
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}
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resource "kubernetes_daemon_set_v1" "kured_sentinel_gate" {
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metadata {
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name = "kured-sentinel-gate"
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namespace = kubernetes_namespace.kured.metadata[0].name
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labels = {
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app = "kured-sentinel-gate"
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tier = local.tiers.cluster
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}
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}
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spec {
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selector {
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match_labels = {
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app = "kured-sentinel-gate"
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}
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}
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template {
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metadata {
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labels = {
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app = "kured-sentinel-gate"
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}
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}
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spec {
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service_account_name = kubernetes_service_account.kured_sentinel_gate.metadata[0].name
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automount_service_account_token = true
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enable_service_links = false
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# bitnami/kubectl:latest runs as uid=1001 by default. The hostPath
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# /var/run is root:root 0755 → final `touch
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# /host/var-run/gated-reboot-required` fails with EACCES, so the gate
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# never opens. Run as root inside the container (the hostPath mount
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# already gives privileged-equivalent access; this just lets us write
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# to /var/run). Found 2026-05-10 during Test 3 validation.
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security_context {
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run_as_user = 0
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}
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toleration {
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effect = "NoSchedule"
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key = "node-role.kubernetes.io/control-plane"
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operator = "Equal"
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}
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toleration {
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effect = "NoSchedule"
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key = "node-role.kubernetes.io/master"
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operator = "Equal"
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}
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container {
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name = "gate"
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image = "bitnami/kubectl:latest"
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image_pull_policy = "Always"
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command = [
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"/bin/bash",
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"-c",
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<<-EOT
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while true; do
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echo "[$(date)] Checking reboot gate conditions..."
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# Check 1: Does the host need a reboot?
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if [ ! -f /host/var-run/reboot-required ]; then
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echo " No reboot required on this host"
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rm -f /host/var-run/gated-reboot-required
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sleep 300
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continue
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fi
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echo " Host has /var/run/reboot-required"
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# Check 2: Are ALL nodes Ready?
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NOT_READY=$(kubectl get nodes --no-headers | grep -v ' Ready' | wc -l | tr -d ' ')
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if [ "$NOT_READY" -gt 0 ]; then
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echo " BLOCKED: $NOT_READY node(s) not Ready"
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rm -f /host/var-run/gated-reboot-required
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sleep 300
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continue
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fi
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echo " All nodes Ready"
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# Check 3: Are ALL calico-node pods Running?
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CALICO_NOT_RUNNING=$(kubectl get pods -n calico-system -l k8s-app=calico-node --no-headers 2>/dev/null | grep -v Running | wc -l | tr -d ' ')
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if [ "$CALICO_NOT_RUNNING" -gt 0 ]; then
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echo " BLOCKED: $CALICO_NOT_RUNNING calico-node pod(s) not Running"
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rm -f /host/var-run/gated-reboot-required
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sleep 300
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continue
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fi
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echo " All calico-node pods Running"
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# Check 4: No node rebooted in last 24 hours (soak window).
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# Stretched from 30m to 24h on 2026-05-10 so the de-facto canary
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# node has a full day of observation before the next node drains.
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RECENT_REBOOT=0
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while IFS= read -r transition_time; do
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if [ -n "$transition_time" ]; then
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transition_epoch=$(date -d "$transition_time" +%s 2>/dev/null || date -j -f "%Y-%m-%dT%H:%M:%SZ" "$transition_time" +%s 2>/dev/null)
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now_epoch=$(date +%s)
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diff=$(( now_epoch - transition_epoch ))
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if [ "$diff" -lt 86400 ]; then
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RECENT_REBOOT=1
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break
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fi
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fi
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done < <(kubectl get nodes -o jsonpath='{range .items[*]}{range .status.conditions[?(@.type=="Ready")]}{.lastTransitionTime}{"\n"}{end}{end}')
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if [ "$RECENT_REBOOT" -eq 1 ]; then
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echo " BLOCKED: A node transitioned Ready within the last 24 hours (soak window)"
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rm -f /host/var-run/gated-reboot-required
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sleep 300
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continue
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fi
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echo " No recent node reboots (24h soak window clear)"
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# All checks passed — create gated sentinel
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echo " ALL CHECKS PASSED — creating /var/run/gated-reboot-required"
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touch /host/var-run/gated-reboot-required
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sleep 300
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done
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EOT
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]
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resources {
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requests = {
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cpu = "10m"
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memory = "32Mi"
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}
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limits = {
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memory = "64Mi"
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}
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}
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volume_mount {
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name = "var-run"
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mount_path = "/host/var-run"
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}
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}
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volume {
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name = "var-run"
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host_path {
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path = "/var/run"
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type = "Directory"
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}
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}
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}
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}
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}
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lifecycle {
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# KYVERNO_LIFECYCLE_V1: Kyverno admission webhook mutates dns_config with ndots=2
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ignore_changes = [spec[0].template[0].spec[0].dns_config]
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}
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}
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