<!--
title: Serverless Framework - Apache OpenWhisk Events - Triggers
menuText: Triggers
menuOrder: 2
description:  Setting up Apache OpenWhisk Triggers and Rules for Function Events
layout: Doc
-->

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### [Read this on the main serverless docs site](https://www.serverless.com/framework/docs/providers/openwhisk/events/streams)

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# Triggers

Functions are connected to event sources in OpenWhisk [using triggers and rules](http://bit.ly/2wcPCJi).
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.

```yaml
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.

```yaml
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.

```yaml
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](http://bit.ly/2f8CSho) of third-party event sources bundled as [packages](http://bit.ly/2wcR8Lq).

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.

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