Using Triggers and sinks¶

In the last topic we used the CloudEvents Player as an event source to send events to the Broker. We now want the event to go from the Broker to an event sink.

In this topic, we will use the CloudEvents Player as the sink as well as a source. This means we will be using the CloudEvents Player to both send and receive events. We will use a Trigger to listen for events in the Broker to send to the sink.

Creating your first Trigger¶

Create a Trigger that listens for CloudEvents from the event source and places them into the sink, which is also the CloudEvents Player app.

knYAML

To create the Trigger, run the command:

kn trigger create cloudevents-trigger --sink cloudevents-player  --broker example-broker

Expected output

Trigger 'cloudevents-trigger' successfully created in namespace 'default'.

Copy the following YAML into a file named ce-trigger.yaml:

apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  name: cloudevents-trigger
  annotations:
    knative-eventing-injection: enabled
spec:
  broker: example-broker
  subscriber:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: cloudevents-player

Create the Trigger by running the command:

kubectl apply -f ce-trigger.yaml

Expected output

trigger.eventing.knative.dev/cloudevents-trigger created

What CloudEvents is my Trigger listening for?

Because we didn't specify a --filter in our kn command, the Trigger is listening for any CloudEvents coming into the Broker.

Expand the next note to see how to use Filters.

Now, when we go back to the CloudEvents Player and send an event, we see that CloudEvents are both sent and received by the CloudEvents Player:

CloudEvents Player user interface

You may need to refresh the page to see your changes.

What if I want to filter on CloudEvent attributes?

First, delete your existing Trigger:

  kn trigger delete cloudevents-trigger

Now let's add a Trigger that listens for a certain CloudEvent Type

  kn trigger create cloudevents-player-filter --sink cloudevents-player  --broker example-broker --filter type=some-type

If you send a CloudEvent with type some-type, it is reflected in the CloudEvents Player UI. The Trigger ignores any other types.

You can filter on any aspect of the CloudEvent you would like to.

Some people call this "Event-Driven Architecture" which can be used to create your own "Functions as a Service" on Kubernetes