Skip to content

Read this on the main serverless docs site

Triggers

Functions are connected to event sources in OpenWhisk using triggers and rules. Triggers create a named event stream within the system. Triggers can be fired manually or connected to external data sources, like databases or message queues.

Rules set up a binding between triggers and serverless functions. With an active rule, each time a trigger is fired, the function will be executed with the trigger payload.

Event binding using triggers and rules for functions can be configured through the serverless.yaml file.

functions:
  my_function:
    handler: index.main
    events:
      - trigger: my_trigger

This configuration will create a trigger called servicename-my_trigger with an active rule binding my_function to this event stream.

Customising Rules

Rule names default to the following format servicename-trigger-to-action. These names can be explicitly set through configuration.

functions:
  my_function:
    handler: index.main
    events:
      - trigger:
        name: 'my_trigger'
        rule: 'rule_name'

Customising Triggers

Triggers can be defined as separate resources in the serverless.yaml file. This allows you to set up trigger properties like default parameters.

functions:
  my_function:
    handler: index.main
    events:
      - trigger: my_trigger

resources:
  triggers:
    my_trigger:
      parameters:
        hello: world

Trigger Feeds

Triggers can be bound to external event sources using the feed property. OpenWhisk provides a catalogue of third-party event sources bundled as packages.

This example demonstrates setting up a trigger which uses the /whisk.system/alarms/alarm feed. The alarm feed will fire a trigger according to a user-supplied cron schedule.

resources:
  triggers:
    alarm_trigger:
      parameters:
        hello: world
      feed: /whisk.system/alarms/alarm
      feed_parameters:
        cron: '*/8 * * * * *'