Suppressing Kapacitor alerts based on hierarchy

Kapacitor allows you to build out a robust monitoring and alerting solution with multiple “levels” or “tiers” of alerts. However, an issue arises when an event triggers both high-level and low-level alerts and you end up getting multiple alerts from different contexts. The AlertNode’s .inhibit() method allows you to suppress other alerts when an alert is triggered.

For example, let’s say you are monitoring a cluster of servers. As part of your alerting architecture, you have host-level alerts such as CPU usage alerts, RAM usage alerts, disk I/O, etc. You also have cluster-level alerts that monitor network health, host uptime, etc.

If a CPU spike on a host in your cluster takes the machine offline, rather than getting a host-level alert for the CPU spike and a cluster-level alert for the offline node, you’d get a single alert – the alert that the node is offline. The cluster-level alert would suppress the host-level alert.

Using the .inhibit() method to suppress alerts

The .inhibit() method uses alert categories and tags to inhibit or suppress other alerts.

// ...
  |alert()
    .inhibit('<category>', '<tags>')

category
The category for which this alert inhibits or suppresses alerts.

tags
A comma-delimited list of tags that must be matched in order for alerts to be inhibited or suppressed.

Example hierarchical alert suppression

The following TICKscripts represent two alerts in a layered alert architecture. The first is a host specific CPU alert that triggers an alert to the system_alerts category whenever idle CPU usage is less than 10%. Streamed data points are grouped by the host tag, which identifies the host the data point is coming from.

cpu_alert.tick

stream
  |from()
    .measurement('cpu')
    .groupBy('host')
  |alert()
    .category('system_alerts')
    .crit(lambda: "usage_idle" < 10.0)

The following TICKscript is a cluster-level alert that monitors the uptime of hosts in the cluster. It uses the deadman() function to create an alert when a host is unresponsive or offline. The .inhibit() method in the deadman alert suppresses all alerts to the system_alerts category that include a matching host tag, meaning they are from the same host.

host_alert.tick

stream
  |from()
    .measurement('uptime')
    .groupBy('host')
  |deadman(0.0, 1m)
    .inhibit('system_alerts', 'host')

With this alert architecture, a host may be unresponsive due to a CPU bottleneck, but because the deadman alert inhibits system alerts from the same host, you won’t get alert notifications for both the deadman and the high CPU usage; just the deadman alert for that specific host.

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