Using Trigger Feeds

Feeds offer a convenient way to configure an external event source to fire these events to a OpenWhisk trigger. This example shows how to use a feed in the Alarms package to fire a trigger every second, and how to use a rule to invoke an action every second.

1. Get a description of the feed in the /whisk.system/alarms package.

$ wsk package get --summary /whisk.system/alarms

package /whisk.system/alarms
 feed   /whisk.system/alarms/alarm

$ wsk action get --summary /whisk.system/alarms/alarm

action /whisk.system/alarms/alarm: Fire trigger when alarm occurs
   (params: cron trigger_payload)

The /whisk.system/alarms/alarm feed takes two parameters:

• cron: A crontab specification of when to fire the trigger.
• trigger_payload: The payload parameter value to set in each trigger event.

2. Create a trigger that fires every eight seconds.

$ wsk trigger create everyEightSeconds --feed /whisk.system/alarms/alarm -p cron '*/8 * * * * *' -p trigger_payload '{"name":"Mork", "place":"Ork"}'

ok: created trigger feed everyEightSeconds

3. Create a ‘hello.js’ file with the following action code.

function main(params) {
    return {payload:  'Hello, ' + params.name + ' from ' + params.place};
}

4. Make sure that the action exists.

$ wsk action update hello hello.js

5. Create a rule that invokes the hello action every time the everyEightSeconds trigger fires.

$ wsk rule create --enable myRule everyEightSeconds hello

ok: created rule myRule
ok: rule myRule is activating

6. Check that the action is being invoked by polling for activation logs.

$ wsk activation poll

You should see activations every eight seconds for the trigger, the rule, and the action. The action receives the parameters {"name":"Mork", "place":"Ork"} on every invocation.