Using the Alarm package

The /whisk.system/alarms package can be used to fire a trigger at a specified frequency. Alarms are 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/interval	feed	minutes, trigger_payload, startDate, stopDate	Fire Trigger event on an interval based schedule.
/whisk.system/alarms/once	feed	date, trigger_payload, deleteAfterFire	Fire Trigger event once on a specific date.
/whisk.system/alarms/alarm	feed	cron, trigger_payload, startDate, stopDate	Fire Trigger event on a time-based schedule using cron.

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

• trigger_payload (optional): The value of this parameter becomes the content of the Trigger every time the Trigger is fired.

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

• stopDate (optional): 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 example creates a trigger that is fired once every 2 minutes. The Trigger fires as soon as possible, and will stop firing January 31, 2019, 23:59:00 UTC.

wsk trigger create interval \
  --feed /whisk.system/alarms/interval \
  --param minutes 2 \
  --param trigger_payload "{\"name\":\"Odin\",\"place\":\"Asgard\"}" \
  --param stopDate "2019-01-31T23:59:00.000Z"

Each generated event includes parameters, which are the properties that are specified by the trigger_payload value. In this case, each Trigger event has the parameters name=Odin and place=Asgard.

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 (required): 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 (optional): The value of this parameter becomes the content of the Trigger when the Trigger is fired.

• deleteAfterFire (optional, default: false): The value of this parameter determines whether the Trigger and potentially all of its associated rules will be deleted after the Trigger is fired.

  • false: No action will be taken after the Trigger fires.
  • true: The Trigger will be deleted after it fires.
  • rules: The Trigger and all of its associated rules will be deleted after it fires.

The following is an example of creating a trigger that will be fired once on December 25, 2019, 12:30:00 UTC. After the Trigger fires it will be deleted as well as all of its associated rules.

wsk trigger create fireOnce \
  --feed /whisk.system/alarms/once \
  --param trigger_payload "{\"name\":\"Odin\",\"place\":\"Asgard\"}" \
  --param date "2019-12-25T12:30:00.000Z" \
  --param deleteAfterFire "rules"

Firing a Trigger on a time-based schedule using cron

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 (required): 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 information, see: http://crontab.org. The following strings are examples that use varying duration's of frequency.

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

  Note: The parameter cron supports five or six fields. Not all OpenWhisk vendors may support 6 fields so please check their documentation for support. 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 (optional): The value of this parameter becomes the content of the Trigger every time the Trigger is fired.

• startDate (optional): The date when the Trigger will start running. The Trigger fires based on the schedule specified by the cron parameter.

• stopDate (optional): The date when the Trigger will stop running. Triggers are no longer fired once this date is 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 fires 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"

Note: The parameter maxTriggers is deprecated and will be removed soon. To stop the Trigger, use the stopDate parameter.