core-deployments/prometheus/service-monitor-longhorn.yaml

---
apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  name: longhorn-prometheus-servicemonitor
  namespace: prometheus
  labels:
    name: longhorn-prometheus-servicemonitor
spec:
  selector:
    matchLabels:
      app: longhorn-manager
  namespaceSelector:
    matchNames:
      - longhorn-system
  endpoints:
    - port: manager