We provide a couple of example Longhorn alert rules below for your references. See here for a list of all available Longhorn metrics and build your own alert rules.

    1. apiVersion: monitoring.coreos.com/v1
    2. kind: PrometheusRule
    3. metadata:
    4.   labels:
    5.     prometheus: longhorn
    6.     role: alert-rules
    7.   name: prometheus-longhorn-rules
    8.   namespace: monitoring
    9. spec:
    10.   groups:
    11.   - name: longhorn.rules
    12.     rules:
    13.     - alert: LonghornVolumeActualSpaceUsedWarning
    14.       annotations:
    15.         description: The actual space used by Longhorn volume {{$labels.volume}} on {{$labels.node}} is at {{$value}}% capacity for
    16.           more than 5 minutes.
    17.         summary: The actual used space of Longhorn volume is over 90% of the capacity.
    18.       expr: (longhorn_volume_actual_size_bytes / longhorn_volume_capacity_bytes) * 100 > 90
    19.       for: 5m
    20.       labels:
    21.         issue: The actual used space of Longhorn volume {{$labels.volume}} on {{$labels.node}} is high.
    22.         severity: warning
    23.     - alert: LonghornVolumeStatusCritical
    24.       annotations:
    25.         description: Longhorn volume {{$labels.volume}} on {{$labels.node}} is Fault for
    26.           more than 2 minutes.
    27.         summary: Longhorn volume {{$labels.volume}} is Fault
    28.       expr: longhorn_volume_robustness == 3
    29.       for: 5m
    30.       labels:
    31.         issue: Longhorn volume {{$labels.volume}} is Fault.
    32.         severity: critical
    33.     - alert: LonghornVolumeStatusWarning
    34.       annotations:
    35.         description: Longhorn volume {{$labels.volume}} on {{$labels.node}} is Degraded for
    36.           more than 5 minutes.
    37.         summary: Longhorn volume {{$labels.volume}} is Degraded
    38.       expr: longhorn_volume_robustness == 2
    39.       for: 5m
    40.       labels:
    41.         issue: Longhorn volume {{$labels.volume}} is Degraded.
    42.         severity: warning
    43.     - alert: LonghornNodeStorageWarning
    44.       annotations:
    45.         description: The used storage of node {{$labels.node}} is at {{$value}}% capacity for
    46.           more than 5 minutes.
    47.         summary:  The used storage of node is over 70% of the capacity.
    48.       expr: (longhorn_node_storage_usage_bytes / longhorn_node_storage_capacity_bytes) * 100 > 70
    49.       for: 5m
    50.       labels:
    51.         issue: The used storage of node {{$labels.node}} is high.
    52.         severity: warning
    53.     - alert: LonghornDiskStorageWarning
    54.       annotations:
    55.         description: The used storage of disk {{$labels.disk}} on node {{$labels.node}} is at {{$value}}% capacity for
    56.           more than 5 minutes.
    57.         summary:  The used storage of disk is over 70% of the capacity.
    58.       expr: (longhorn_disk_usage_bytes / longhorn_disk_capacity_bytes) * 100 > 70
    59.       for: 5m
    60.       labels:
    61.         issue: The used storage of disk {{$labels.disk}} on node {{$labels.node}} is high.
    62.         severity: warning
    63.     - alert: LonghornNodeDown
    64.       annotations:
    65.         description: There are {{$value}} Longhorn nodes which have been offline for more than 5 minutes.
    66.         summary: Longhorn nodes is offline
    67.       expr: longhorn_node_total - (count(longhorn_node_status{condition="ready"}==1) OR on() vector(0))
    68.       for: 5m
    69.       labels:
    70.         issue: There are {{$value}} Longhorn nodes are offline
    71.         severity: critical
    72.     - alert: LonghornIntanceManagerCPUUsageWarning
    73.       annotations:
    74.         description: Longhorn instance manager {{$labels.instance_manager}} on {{$labels.node}} has CPU Usage / CPU request is {{$value}}% for
    75.           more than 5 minutes.
    76.         summary: Longhorn instance manager {{$labels.instance_manager}} on {{$labels.node}} has CPU Usage / CPU request is over 300%.
    77.       expr: (longhorn_instance_manager_cpu_usage_millicpu/longhorn_instance_manager_cpu_requests_millicpu) * 100 > 300
    78.       for: 5m
    79.       labels:
    80.         issue: Longhorn instance manager {{$labels.instance_manager}} on {{$labels.node}} consumes 3 times the CPU request.
    81.         severity: warning
    82.     - alert: LonghornNodeCPUUsageWarning
    83.       annotations:
    84.         description: Longhorn node {{$labels.node}} has CPU Usage / CPU capacity is {{$value}}% for
    85.           more than 5 minutes.
    86.         summary: Longhorn node {{$labels.node}} experiences high CPU pressure for more than 5m.
    87.       expr: (longhorn_node_cpu_usage_millicpu / longhorn_node_cpu_capacity_millicpu) * 100 > 90
    88.       for: 5m
    89.       labels:
    90.         issue: Longhorn node {{$labels.node}} experiences high CPU pressure.
    91.         severity: warning

    See more about how to define alert rules at here.