apiVersion: monitoring.coreos.com/v1
kind: PrometheusRule
metadata:
  labels:
    prometheus: k8s
    role: alert-rules
  name: example-rule
spec:
  groups:
  - name: example-rule
    rules:
    - alert: example-alert
      annotations:
        description: Memory on node {{ $labels.instance }} currently at {{ $value }}% 
          is under pressure
        summary: Memory usage is under pressure, system may become unstable.
      expr: |
        100 - ((node_memory_MemAvailable_bytes{job="node-exporter"} * 100) / node_memory_MemTotal_bytes{job="node-exporter"}) > 70
      for: 2m
      labels:
        severity: warning