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 feed.
| Entity | Type | Parameters | Description |
|---|---|---|---|
/whisk.system/alarms |
package | - | Alarms and periodic utility |
/whisk.system/alarms/alarm |
feed | cron, trigger_payload, maxTriggers | Fire trigger event periodically |
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
-
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 1,000,000. You can set it to infinite (-1).
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.
wsk trigger create periodic \
--feed /whisk.system/alarms/alarm \
--param cron "*/2 * * * *" \
--param trigger_payload "{\"name\":\"Odin\",\"place\":\"Asgard\"}"
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.
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.