---
apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  name: longhorn
  namespace: base-system
  labels:
    app.kubernetes.io/created-by: tyil
    app.kubernetes.io/managed-by: manual
    app.kubernetes.io/name: longhorn
    app.kubernetes.io/part-of: base-system
spec:
  selector:
    matchLabels:
      app: longhorn-manager
  namespaceSelector:
    matchNames:
    - base-system
  endpoints:
  - port: manager
...