Log event handler

The log event handler writes to a specified log file with one alert event per line. If the specified log file does not exist, it will be created.

Options

The following log event handler options can be set in a handler file or when using .log() in a TICKscript.

Example: handler file

id: handler-id
topic: topic-name
kind: log
options:
  path: '/tmp/alerts.log'
  mode: 0644

Example: TICKscript

|alert()
  // ...
  .log('/tmp/alerts.log')
    .mode(0644)

Using the log event handler

The log event handler can be used in both TICKscripts and handler files to log messages to a log file.

Log messages from a TICKscript

The following TICKscript uses the .log() event handler to log a message to the /tmp/alerts.log log file whenever idle CPU usage drops below 10%.

log-cpu-alert.tick

stream
  |from()
    .measurement('cpu')
  |alert()
    .crit(lambda: "usage_idle" < 10)
    .message('{{ .Time }}: CPU usage over 90%')
    .log('/tmp/alerts.log')

Log messages from a defined handler

The following setup sends an alert to the cpu topic with the message, “’{{ .Time }}: CPU usage over 90%’”. A log handler is added that subscribes to the cpu topic and logs messages to /tmp/alerts.log whenever a new message is published.

Create a TICKscript that publishes alert messages to a topic. The TICKscript below sends an alert message to the cpu topic any time idle CPU usage drops below 10%.

cpu_alert.tick

stream
  |from()
    .measurement('cpu')
  |alert()
    .crit(lambda: "usage_idle" < 10)
    .message('{{ .Time }}: CPU usage over 90%')
    .topic('cpu')

Add and enable the TICKscript:

kapacitor define cpu_alert -tick cpu_alert.tick
kapacitor enable cpu_alert

Create a handler file that subscribes to the cpu topic and uses the log event handler to log messages to the /tmp/alerts.log log file.

log_cpu_handler.yaml

id: log-cpu-alert
topic: cpu
kind: log
options:
  path: '/tmp/alerts.log'

Add the handler:

kapacitor define-topic-handler log_cpu_handler.yaml