Simple demo showing OpenWhisk actions, triggers, and rules.
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Simple demo showing OpenWhisk actions, triggers, and rules.

High level diagram

Action: handler.js

This simple JavaScript function (called an action in OpenWhisk parlance) accepts a params argument and writes information that can be retrieved from OpenWhisk logs and/or the IBM Bluemix monitoring console. It also returns a JSON object with the current date.

This action can be uploaded to OpenWhisk using the following command:

wsk action create handler handler.js

It can be manually invoked during testing in a synchronous manner. This will echo the resulting JSON message:

wsk action invoke --blocking handler

The console.log statements will be logged to the OpenWhisk activation log, which you can stream with the following command:

wsk activation poll

Trigger: every-20-seconds

This trigger uses the built in alarm package feed to fire events every 20 seconds which is specified by a cron syntax in the cron parameter passed when it is created. The maxTriggers parameter ensures that it only fires for two minutes, rather than the default of 10,000 invocations.

The trigger can be created with the following command:

wsk trigger create every-20-seconds \
    --feed  /whisk.system/alarms/alarm \
    --param cron '*/20 * * * * *' \
    --param maxTriggers 6

Rule: invoke-periodically

This rule shows how the every-20-seconds trigger can be declaratively mapped to the handler.js action. Notice that it's named somewhat abstractly so that if we wanted to use a different trigger, perhaps something that fires every minute instead, we could still keep the logical name.

The rule can be created with the following command:

wsk rule create \
    invoke-periodically \
    every-20-seconds \

At this point you can check the activation log to see if indeed the action is invoked by our trigger:

wsk activation poll

Installation instructions

OpenWhisk developers will often automate the creation of actions, triggers, and rules as they iterate on their application. The convention that has arisen in many sample apps is to use a script, often in conjunction with a local.env file to externalize environment variables.

The script can be used to set up, tear down, and see the current configuration:

./ --install
./ --uninstall
./ --env # Not used in this demo

Install the wsk CLI from Bluemix

After registering for Bluemix, navigate to the "OpenWhisk" section. You'll find it in the left navigation, under the three horizontal bar (hamburger icon).

Click the "Download OpenWhisk CLI" button and place the wsk binary in your path, such as in ~/bin. Open a terminal and set your namespace and authorization as shown in step 2. Then create your first action in step 3.