Basic alerts to use with Prometheus Blackbox Exporter

vmrule-blackbox-exporter-alerts.yaml

---
apiVersion: operator.victoriametrics.com/v1beta1
kind: VMRule
metadata:
  name: blackbox-exporter-alerts
  namespace: monitoring
  labels:
    app.kubernetes.io/name: blackbox-exporter
    app.kubernetes.io/component: alert-rules
spec:
  groups:
    - name: blackbox-exporter
      interval: 60s
      rules:
        - alert: ProbeDown
          expr: probe_success == 0
          for: 5m
          labels:
            severity: critical
            component: blackbox-exporter
          annotations:
            summary: "Probe target {{ $labels.target }} is down"
            description: "{{ $labels.target }} ({{ $labels.instance }}) has been unreachable for more than 5 minutes."

        - alert: ProbeSlow
          expr: probe_duration_seconds > 10
          for: 5m
          labels:
            severity: warning
            component: blackbox-exporter
          annotations:
            summary: "Probe target {{ $labels.target }} is slow"
            description: "{{ $labels.target }} ({{ $labels.instance }}) probe duration is {{ $value | humanizeDuration }}, exceeding the 10s threshold."

        # step-ca issues ~30-day certs; cert-manager renews at ~20 days remaining (2/3 of duration).
        # Thresholds below the 20-day renewal point indicate cert-manager or external renewal has failed.
        - alert: SSLCertExpiringWarning
          expr: (probe_ssl_earliest_cert_expiry - time()) / 86400 < 10
          for: 1h
          labels:
            severity: warning
            component: blackbox-exporter
          annotations:
            summary: "SSL certificate for {{ $labels.target }} expires soon"
            description: "SSL certificate for {{ $labels.target }} ({{ $labels.instance }}) expires in {{ $value | humanize }} days. cert-manager should have renewed it already."

        - alert: SSLCertExpiringCritical
          expr: (probe_ssl_earliest_cert_expiry - time()) / 86400 < 5
          for: 1h
          labels:
            severity: critical
            component: blackbox-exporter
          annotations:
            summary: "SSL certificate for {{ $labels.target }} is about to expire"
            description: "SSL certificate for {{ $labels.target }} ({{ $labels.instance }}) expires in {{ $value | humanize }} days. Immediate action required."