Triggers - Develop | Serverless | OpenShift Container Platform 4.8

Creating a trigger by using the web console
Creating a trigger by using the Knative cli
Listing triggers by using the Knative cli
Describing a trigger by using the Knative cli
Filtering events with triggers by using the Knative cli
Updating a trigger by using the Knative cli
Deleting a trigger by using the Knative cli
Configuring event delivery ordering for triggers
Next steps

Brokers can be used in combination with triggers to deliver events from an event source to an event sink. Events are sent from an event source to a broker as an HTTP POST request. After events have entered the broker, they can be filtered by CloudEvent attributes using triggers, and sent as an HTTP POST request to an event sink.

If you are using a Kafka broker, you can configure the delivery order of events from triggers to event sinks. See Configuring event delivery ordering for triggers.

Creating a trigger by using the web console

Using the OpenShift Container Platform web console provides a streamlined and intuitive user interface to create a trigger. After Knative Eventing is installed on your cluster and you have created a broker, you can create a trigger by using the web console.

Prerequisites

The OpenShift Serverless Operator, Knative Serving, and Knative Eventing are installed on your OpenShift Container Platform cluster.
You have logged in to the web console.
You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.
You have created a broker and a Knative service or other event sink to connect to the trigger.

Procedure

In the Developer perspective, navigate to the Topology page.
Hover over the broker that you want to create a trigger for, and drag the arrow. The Add Trigger option is displayed.
click Add Trigger.
Select your sink in the Subscriber list.
click Add.

Verification

After the subscription has been created, you can view it in the Topology page, where it is represented as a line that connects the broker to the event sink.

Deleting a trigger

In the Developer perspective, navigate to the Topology page.
click on the trigger that you want to delete.
In the Actions context menu, select Delete Trigger.

Creating a trigger by using the Knative cli

Using the Knative (kn) cli to create triggers provides a more streamlined and intuitive user interface over modifying YAML files directly. You can use the kn trigger create command to create a trigger.

Prerequisites

The OpenShift Serverless Operator and Knative Eventing are installed on your OpenShift Container Platform cluster.
You have installed the Knative (kn) cli.
You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.

Procedure

Create a trigger:
```
$ kn trigger create <trigger_name> --broker <broker_name> --filter <key=value> --sink <sink_name>
```
Alternatively, you can create a trigger and simultaneously create the default broker using broker injection:
```
$ kn trigger create <trigger_name> --inject-broker --filter <key=value> --sink <sink_name>
```
By default, triggers forward all events sent to a broker to sinks that are subscribed to that broker. Using the --filter attribute for triggers allows you to filter events from a broker, so that subscribers will only receive a subset of events based on your defined criteria.

Listing triggers by using the Knative cli

Using the Knative (kn) cli to list triggers provides a streamlined and intuitive user interface. You can use the kn trigger list command to list existing triggers in your cluster.

Prerequisites

The OpenShift Serverless Operator and Knative Eventing are installed on your OpenShift Container Platform cluster.
You have installed the Knative (kn) cli.

Procedure

Print a list of available triggers:

$ kn trigger list

Example output

NAME    BROKER    SINK           AGE   CONDITIONS   READY   REASON
email   default   ksvc:edisplay   4s    5 OK / 5     True
ping    default   ksvc:edisplay   32s   5 OK / 5     True

Optional: Print a list of triggers in JSON format:
```
$ kn trigger list -o json
```

Describing a trigger by using the Knative cli

Using the Knative (kn) cli to describe triggers provides a streamlined and intuitive user interface. You can use the kn trigger describe command to print information about existing triggers in your cluster by using the Knative cli.

Prerequisites

The OpenShift Serverless Operator and Knative Eventing are installed on your OpenShift Container Platform cluster.
You have installed the Knative (kn) cli.
You have created a trigger.

Procedure

Enter the command:

$ kn trigger describe <trigger_name>

Example output

Name:         ping
Namespace:    default
Labels:       eventing.knative.dev/broker=default
Annotations:  eventing.knative.dev/creator=kube:admin, eventing.knative.dev/lastModifier=kube:admin
Age:          2m
Broker:       default
Filter:
  type:       dev.knative.event

Sink:
  Name:       edisplay
  Namespace:  default
  Resource:   Service (serving.knative.dev/v1)

Conditions:
  OK TYPE                  AGE REASON
  ++ Ready                  2m
  ++ BrokerReady            2m
  ++ DependencyReady        2m
  ++ Subscribed             2m
  ++ SubscriberResolved     2m

Filtering events with triggers by using the Knative cli

Using the Knative (kn) cli to filter events by using triggers provides a streamlined and intuitive user interface. You can use the kn trigger create command, along with the appropriate flags, to filter events by using triggers.

In the following trigger example, only events with the attribute type: dev.knative.samples.helloworld are sent to the event sink:

$ kn trigger create <trigger_name> --broker <broker_name> --filter type=dev.knative.samples.helloworld --sink ksvc:<service_name>

You can also filter events by using multiple attributes. The following example shows how to filter events using the type, source, and extension attributes:

$ kn trigger create <trigger_name> --broker <broker_name> --sink ksvc:<service_name> \
--filter type=dev.knative.samples.helloworld \
--filter source=dev.knative.samples/helloworldsource \
--filter myextension=my-extension-value

Updating a trigger by using the Knative cli

Using the Knative (kn) cli to update triggers provides a streamlined and intuitive user interface. You can use the kn trigger update command with certain flags to update attributes for a trigger.

Prerequisites

The OpenShift Serverless Operator and Knative Eventing are installed on your OpenShift Container Platform cluster.
You have installed the Knative (kn) cli.
You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.

Procedure

Update a trigger:
```
$ kn trigger update <trigger_name> --filter <key=value> --sink <sink_name> [flags]
```
- You can update a trigger to filter exact event attributes that match incoming events. For example, using the type attribute:
  $ kn trigger update <trigger_name> --filter type=knative.dev.event
- You can remove a filter attribute from a trigger. For example, you can remove the filter attribute with key type:
  $ kn trigger update <trigger_name> --filter type-
- You can use the --sink parameter to change the event sink of a trigger:
  $ kn trigger update <trigger_name> --sink ksvc:my-event-sink

Deleting a trigger by using the Knative cli

Using the Knative (kn) cli to delete a trigger provides a streamlined and intuitive user interface. You can use the kn trigger delete command to delete a trigger.

Prerequisites

The OpenShift Serverless Operator and Knative Eventing are installed on your OpenShift Container Platform cluster.
You have installed the Knative (kn) cli.
You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.

Procedure

Delete a trigger:
```
$ kn trigger delete <trigger_name>
```

Verification

List existing triggers:
```
$ kn trigger list
```
Verify that the trigger no longer exists:
Example output
```
No triggers found.
```

Configuring event delivery ordering for triggers

If you are using a Kafka broker, you can configure the delivery order of events from triggers to event sinks.

Prerequisites

The OpenShift Serverless Operator, Knative Eventing, and Knative Kafka are installed on your OpenShift Container Platform cluster.
Kafka broker is enabled for use on your cluster, and you have created a Kafka broker.
You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.
You have installed the OpenShift (oc) cli.

Procedure

Create or modify a Trigger object and set the kafka.eventing.knative.dev/delivery.order annotation:
```
apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  name: <trigger_name>
  annotations:
     kafka.eventing.knative.dev/delivery.order: ordered
...
```
The supported consumer delivery guarantees are:

unordered

An unordered consumer is a non-blocking consumer that delivers messages unordered, while preserving proper offset management.

ordered

An ordered consumer is a per-partition blocking consumer that waits for a successful response from the CloudEvent subscriber before it delivers the next message of the partition.

The default ordering guarantee is unordered.
Apply the Trigger object:
```
$ oc apply -f <filename>
```

Next steps

Configure event delivery parameters that are applied in cases where an event fails to be delivered to an event sink. See Examples of configuring event delivery parameters.