Event delivery workflows using brokers and triggers - Event workflows | Serverless

Creating a broker
Managing brokers
Filtering events using triggers

Brokers can be used in combination with triggers to deliver events from an event source to an event sink.

Events can be 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.

Creating a broker

OpenShift Serverless provides a default Knative broker that can be created by using the Knative CLI. You can also create the default broker by adding the eventing.knative.dev/injection=enabled label to a namespace if you are a cluster administrator, or by adding the eventing.knative.dev/injection: enabled annotation to a trigger if you are a developer.

Although both developers and cluster administrators can add a broker by injection, only cluster administrators can permanently delete brokers that were created using this method.

Creating a broker using the Knative CLI

Prerequisites

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

Procedure

Create the default broker:
```
$ kn broker create default
```

Verification

Use the kn command to list all existing brokers:

$ kn broker list

Example output

NAME      URL                                                                     AGE   CONDITIONS   READY   REASON
default   http://broker-ingress.knative-eventing.svc.cluster.local/test/default   45s   5 OK / 5     True

Optional: If you are using the OpenShift Container Platform web console, you can navigate to the Topology view in the Developer perspective, and observe that the broker exists:

Creating a broker by annotating a trigger

You can create a broker by adding the eventing.knative.dev/injection: enabled annotation to a Trigger object.

If you create a broker by using the eventing.knative.dev/injection: enabled annotation, you cannot delete this broker without cluster administrator permissions. If you delete the broker without having a cluster administrator remove this annotation first, the broker is created again after deletion.

Prerequisites

The OpenShift Serverless Operator and Knative Eventing are installed on your OpenShift Container Platform cluster.

Procedure

Create a Trigger object as a .yaml file that has the eventing.knative.dev/injection: enabled annotation:

apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  annotations:
    eventing.knative.dev/injection: enabled
  name: <trigger-name>
spec:
  broker: default
  subscriber: (1)
    ref:
      apiVersion: serving.knative.dev/v1
      kind: service
      name: <service-name>

1	Specify details about the event sink, or subscriber, that the trigger sends events to.

Apply the .yaml file:
```
$ oc apply -f <filename>
```

Verification

You can verify that the broker has been created successfully by using the oc CLI, or by observing it in the Topology view in the web console.

Use the oc command to get the broker:

$ oc -n <namespace> get broker default

Example output

NAME      READY     REASON    URL                                                                     AGE
default   True                http://broker-ingress.knative-eventing.svc.cluster.local/test/default   3m56s

Navigate to the Topology view in the web console, and observe that the broker exists:

Creating a broker by labeling a namespace

If you have cluster administrator permissions, you can create the default broker automatically by labeling a namespace.

Brokers created using this method will not be removed if you remove the label. You must manually delete them.

Prerequisites

The OpenShift Serverless Operator and Knative Eventing are installed on your OpenShift Container Platform cluster.
You have cluster administrator permissions for OpenShift Container Platform.

Procedure

Label a namespace with eventing.knative.dev/injection=enabled:

$ oc label namespace <namespace> eventing.knative.dev/injection=enabled

Verification

You can verify that the broker has been created successfully by using the oc CLI, or by observing it in the Topology view in the web console.

Use the oc command to get the broker:

$ oc -n <namespace> get broker <broker_name>

Example command

$ oc -n default get broker default

Example output

NAME      READY     REASON    URL                                                                     AGE
default   True                http://broker-ingress.knative-eventing.svc.cluster.local/test/default   3m56s

Navigate to the Topology view in the web console, and observe that the broker exists:

Managing brokers

The kn CLI provides commands that can be used to list, describe, update, and delete brokers. Cluster administrators can also permanently delete a broker that was created using injection.

Listing existing brokers using the Knative CLI

Prerequisites

The OpenShift Serverless Operator, Knative Serving and Knative Eventing are installed on your OpenShift Container Platform cluster.
You have installed the kn CLI.

Procedure

List all existing brokers:

$ kn broker list

Example output

NAME      URL                                                                     AGE   CONDITIONS   READY   REASON
default   http://broker-ingress.knative-eventing.svc.cluster.local/test/default   45s   5 OK / 5     True

Describing an existing broker using the Knative CLI

Prerequisites

The OpenShift Serverless Operator, Knative Serving and Knative Eventing are installed on your OpenShift Container Platform cluster.
You have installed the kn CLI.

Procedure

Describe an existing broker:

$ kn broker describe <broker_name>

Example command using default broker

$ kn broker describe default

Example output

Name:         default
Namespace:    default
Annotations:  eventing.knative.dev/broker.class=MTChannelBasedBroker, eventing.knative.dev/creato ...
Age:          22s

Address:
  URL:    http://broker-ingress.knative-eventing.svc.cluster.local/default/default

Conditions:
  OK TYPE                   AGE REASON
  ++ Ready                  22s
  ++ Addressable            22s
  ++ FilterReady            22s
  ++ IngressReady           22s
  ++ TriggerChannelReady    22s

Deleting a broker that was created by injection

Brokers created by injection, by using a namespace label or trigger annotation, are not deleted permanently if a developer removes the label or annotation. A user with cluster administrator permissions must manually delete these brokers.

Procedure

Remove the eventing.knative.dev/injection=enabled label from the namespace:
```
$ oc label namespace <namespace> eventing.knative.dev/injection-
```
Removing the annotation prevents Knative from recreating the broker after you delete it.

Delete the broker from the selected namespace:

$ oc -n <namespace> delete broker <broker_name>

Verification

Use the oc command to get the broker:

$ oc -n <namespace> get broker <broker_name>

Example command

$ oc -n default get broker default

Example output

No resources found.
Error from server (NotFound): brokers.eventing.knative.dev "default" not found

Filtering events using triggers

Using triggers enables you to filter events from the broker for delivery to event sinks.

Prerequisites

Before you can use triggers, you will need:

Knative Eventing and kn installed.
An available broker, either the default broker or one that you have created.

You can create the default broker either by following the instructions on Using brokers with Knative Eventing, or by using the --inject-broker flag while creating a trigger. Use of this flag is described later in this section.
An available event consumer, such as a Knative service.

Creating a trigger using the Developer perspective

After you have created a broker, you can create a trigger in the web console Developer perspective.

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 are in the Developer perspective.
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 as a Subscriber from the drop-down list.
Click Add.

Verification

After the subscription has been created, it is represented as a line that connects the broker to the service in the Topology view:

Deleting a trigger using the Developer perspective

You can delete triggers in the web console Developer perspective.

Prerequisites

To delete a trigger using the Developer perspective, ensure that you have logged in to the web console.

Procedure

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 using kn

You can create a trigger by using the kn trigger create command.

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 using kn

The kn trigger list command prints a list of available triggers.

Procedure

To print a list of available triggers, enter the following command:

$ 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 using kn

You can use the kn trigger describe command to print information about a trigger.

Procedure

To print information about a trigger, enter the following 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 using triggers

In the following trigger example, only events with attribute type: dev.knative.samples.helloworld will reach the event consumer.

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

You can also filter events 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 using kn

You can use the kn trigger update command with certain flags to quickly update attributes of a trigger.

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 mytrigger --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 mytrigger --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 using kn

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.
```