Using the Alarm package

The /whisk.system/alarms package can be used to fire a trigger at a specified frequency. This is useful for setting up recurring jobs or tasks, such as invoking a system backup action every hour.

The package includes the following feeds.

Entity	Type	Parameters	Description
/whisk.system/alarms	package	-	Alarms and periodic utility
/whisk.system/alarms/alarm	feed	cron, trigger_payload, maxTriggers, startDate, stopDate	Fire trigger event periodically
/whisk.system/alarms/once	feed	date, trigger_payload	Fire trigger event once on a specific date
/whisk.system/alarms/interval	feed	minutes, trigger_payload, startDate, stopDate	Fire trigger event on an interval based schedule

Firing a trigger event periodically on a time based schedule

The /whisk.system/alarms/alarm feed configures the Alarm service to fire a trigger event at a specified frequency. The parameters are as follows:

• cron: A string, based on the UNIX crontab syntax, that indicates when to fire the trigger in Coordinated Universal Time (UTC). The string is a sequence of five fields that are separated by spaces: X X X X X. For more details about using cron syntax, see: http://crontab.org. Following are some examples of the frequency that is indicated by the string:

  • * * * * *: top of every minute.
  • 0 * * * *: top of every hour.
  • 0 */2 * * *: every 2 hours (i.e. 02:00:00, 04:00:00, ...)
  • 0 9 8 * *: at 9:00:00AM (UTC) on the eighth day of every month

  Note: The parameter cron also supports a custom syntax of six fields, where the first field represents seconds. For more details about using this custom cron syntax, see: https://github.com/ncb000gt/node-cron. Here is an example using six fields notation:

  • */30 * * * * *: every thirty seconds.

• trigger_payload: The value of this parameter becomes the content of the trigger every time the trigger is fired.

• maxTriggers: Stop firing triggers when this limit is reached. Defaults to infinite (-1).

• startDate: The date when the trigger will start running. The trigger will fire based on the schedule specified by the cron parameter.

• stopDate: The date when the trigger will stop running. Triggers will no longer be fired once this date has been reached.

  Note: The startDate and stopDate parameters support an integer or string value. The integer value represents the number of milliseconds since 1 January 1970 00:00:00 UTC and the string value should be in the ISO 8601 format (http://www.ecma-international.org/ecma-262/5.1/#sec-15.9.1.15).

The following is an example of creating a trigger that will be fired once every 2 minutes with name and place values in the trigger event. The trigger will not start firing until January 1, 2019, 00:00:00 UTC and will stop firing January 31, 2019, 23:59:00 UTC.

wsk trigger create periodic \
  --feed /whisk.system/alarms/alarm \
  --param cron "*/2 * * * *" \
  --param trigger_payload "{\"name\":\"Odin\",\"place\":\"Asgard\"}" \
  --param startDate "2019-01-01T00:00:00.000Z" \
  --param stopDate "2019-01-31T23:59:00.000Z"

Each generated event will include as parameters the properties specified in the trigger_payload value. In this case, each trigger event will have parameters name=Odin and place=Asgard.

Firing a trigger event periodically on an interval based schedule

The /whisk.system/alarms/interval feed configures the Alarm service to fire a trigger event on an interval based schedule. The parameters are as follows:

• minutes: An integer representing the length of the interval (in minutes) between trigger fires.

• trigger_payload: The value of this parameter becomes the content of the trigger every time the trigger is fired.

• startDate: The date when the first trigger will be fired. Subsequent fires will occur based on the interval length specified by the minutes parameter.

• stopDate: The date when the trigger will stop running. Triggers will no longer be fired once this date has been reached.

  Note: The startDate and stopDate parameters support an integer or string value. The integer value represents the number of milliseconds since 1 January 1970 00:00:00 UTC and the string value should be in the ISO 8601 format (http://www.ecma-international.org/ecma-262/5.1/#sec-15.9.1.15).

The following is an example of creating a trigger that will be fired once every 90 minutes. The trigger will not start firing until January 1, 2019, 00:00:00 UTC and will stop firing January 31, 2019, 23:59:00 UTC.

wsk trigger create interval \
  --feed /whisk.system/alarms/interval \
  --param minutes 90 \
  --param trigger_payload "{\"name\":\"Odin\",\"place\":\"Asgard\"}" \
  --param startDate "2019-01-01T00:00:00.000Z" \
  --param stopDate "2019-01-31T23:59:00.000Z"

Firing a trigger event once

The /whisk.system/alarms/once feed configures the Alarm service to fire a trigger event on a specified date. The parameters are as follows:

• date: The date when the trigger will be fired. The trigger will be fired just once at the given time.

  Note: The date parameter supports an integer or string value. The integer value represents the number of milliseconds since 1 January 1970 00:00:00 UTC and the string value should be in the ISO 8601 format (http://www.ecma-international.org/ecma-262/5.1/#sec-15.9.1.15).

• trigger_payload: The value of this parameter becomes the content of the trigger when the trigger is fired.

The following is an example of creating a trigger that will be fired once on December 25, 2017, 12:30:00 UTC.

wsk trigger create fireOnce \
  --feed /whisk.system/alarms/once \
  --param trigger_payload "{\"name\":\"Odin\",\"place\":\"Asgard\"}" \
  --param date "2017-12-25T12:30:00.000Z"