Creating a ping source - Develop | Serverless | OpenShift Container Platform 4.6

Creating a ping source by using the web console
Creating a ping source by using the Knative CLI
- Knative CLI sink flag
Creating a ping source by using YAML

A ping source is an event source that can be used to periodically send ping events with a constant payload to an event consumer. A ping source can be used to schedule sending events, similar to a timer.

Creating a ping source by using the web console

After Knative Eventing is installed on your cluster, you can create a ping source by using the web console. Using the OpenShift Container Platform web console provides a streamlined and intuitive user interface to create an event source.

Prerequisites

You have logged in to the OpenShift Container Platform web console.
The OpenShift Serverless Operator, Knative Serving and Knative Eventing are installed on the cluster.
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

To verify that the ping source is working, create a simple Knative service that dumps incoming messages to the logs of the service.

In the Developer perspective, navigate to +Add → YAML.

Copy the example YAML:

apiVersion: serving.knative.dev/v1
kind: service
metadata:
  name: event-display
spec:
  template:
    spec:
      containers:
        - image: quay.io/openshift-knative/knative-eventing-sources-event-display:latest

Click Create.

Create a ping source in the same namespace as the service created in the previous step, or any other sink that you want to send events to.
1. In the Developer perspective, navigate to +Add → Event Source.
2. Select Ping Source.
3. Optional: You can enter a value for Data, which is the message payload.
4. Enter a value for Schedule. In this example, the value is */2 * * * *, which creates a ping source that sends a message every two minutes.
5. Select a Sink. This can be either a Resource or a URI. In this example, the event-display service created in the previous step is used as the Resource sink.
6. Click Create.

Verification

You can verify that the ping source was created and is connected to the sink by viewing the Topology page.

In the Developer perspective, navigate to Topology.
View the ping source and sink.

Deleting the ping source

Navigate to the Topology view.
Right-click the API server source and select Delete Ping Source.

Creating a ping source by using the Knative CLI

You can use the kn source ping create command to create a ping source by using the Knative (kn) CLI. Using the Knative CLI to create event sources provides a more streamlined and intuitive user interface than modifying YAML files directly.

Prerequisites

The OpenShift Serverless Operator, Knative Serving and Knative Eventing are installed on the 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.
Optional: If you want to use the verification steps for this procedure, install the OpenShift CLI (oc).

Procedure

To verify that the ping source is working, create a simple Knative service that dumps incoming messages to the service logs:

$ kn service create event-display \
    --image quay.io/openshift-knative/knative-eventing-sources-event-display:latest

For each set of ping events that you want to request, create a ping source in the same namespace as the event consumer:

$ kn source ping create test-ping-source \
    --schedule "*/2 * * * *" \
    --data '{"message": "Hello world!"}' \
    --sink ksvc:event-display

Check that the controller is mapped correctly by entering the following command and inspecting the output:

$ kn source ping describe test-ping-source

Example output

Name:         test-ping-source
Namespace:    default
Annotations:  sources.knative.dev/creator=developer, sources.knative.dev/lastModifier=developer
Age:          15s
Schedule:     */2 * * * *
Data:         {"message": "Hello world!"}

Sink:
  Name:       event-display
  Namespace:  default
  Resource:   service (serving.knative.dev/v1)

Conditions:
  OK TYPE                 AGE REASON
  ++ Ready                 8s
  ++ Deployed              8s
  ++ SinkProvided         15s
  ++ ValidSchedule        15s
  ++ EventTypeProvided    15s
  ++ ResourcesCorrect     15s

Verification

You can verify that the Kubernetes events were sent to the Knative event sink by looking at the logs of the sink pod.

By default, Knative services terminate their pods if no traffic is received within a 60 second period. The example shown in this guide creates a ping source that sends a message every 2 minutes, so each message should be observed in a newly created pod.

Watch for new pods created:
```
$ watch oc get pods
```

Cancel watching the pods using Ctrl+C, then look at the logs of the created pod:

$ oc logs $(oc get pod -o name | grep event-display) -c user-container

Example output

☁️  cloudevents.Event
Validation: valid
Context Attributes,
  specversion: 1.0
  type: dev.knative.sources.ping
  source: /apis/v1/namespaces/default/pingsources/test-ping-source
  id: 99e4f4f6-08ff-4bff-acf1-47f61ded68c9
  time: 2020-04-07T16:16:00.000601161Z
  datacontenttype: application/json
Data,
  {
    "message": "Hello world!"
  }

Deleting the ping source

Delete the ping source:

$ kn delete pingsources.sources.knative.dev <ping_source_name>

Knative CLI sink flag

When you create an event source by using the Knative (kn) CLI, you can specify a sink where events are sent to from that resource by using the --sink flag. The sink can be any addressable or callable resource that can receive incoming events from other resources.

The following example creates a sink binding that uses a service, http://event-display.svc.cluster.local, as the sink:

Example command using the sink flag

$ kn source binding create bind-heartbeat \
  --namespace sinkbinding-example \
  --subject "Job:batch/v1:app=heartbeat-cron" \
  --sink http://event-display.svc.cluster.local \ (1)
  --ce-override "sink=bound"

1	`svc` in `http://event-display.svc.cluster.local` determines that the sink is a Knative service. Other default sink prefixes include `channel`, and `broker`.

Creating a ping source by using YAML

Creating Knative resources by using YAML files uses a declarative API, which enables you to describe event sources declaratively and in a reproducible manner. To create a serverless ping source by using YAML, you must create a YAML file that defines a PingSource object, then apply it by using oc apply.

Example PingSource object

apiVersion: sources.knative.dev/v1
kind: PingSource
metadata:
  name: test-ping-source
spec:
  schedule: "*/2 * * * *" (1)
  data: '{"message": "Hello world!"}' (2)
  sink: (3)
    ref:
      apiVersion: serving.knative.dev/v1
      kind: service
      name: event-display

1	The schedule of the event specified using CRON expression.
2	The event message body expressed as a JSON encoded data string.
3	These are the details of the event consumer. In this example, we are using a Knative service named `event-display`.

Prerequisites

The OpenShift Serverless Operator, Knative Serving and Knative Eventing are installed on the cluster.
Install the OpenShift CLI (oc).
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

To verify that the ping source is working, create a simple Knative service that dumps incoming messages to the service’s logs.

Create a service YAML file:

apiVersion: serving.knative.dev/v1
kind: service
metadata:
  name: event-display
spec:
  template:
    spec:
      containers:
        - image: quay.io/openshift-knative/knative-eventing-sources-event-display:latest

Create the service:
```
$ oc apply -f <filename>
```

For each set of ping events that you want to request, create a ping source in the same namespace as the event consumer.

Create a YAML file for the ping source:

apiVersion: sources.knative.dev/v1
kind: PingSource
metadata:
  name: test-ping-source
spec:
  schedule: "*/2 * * * *"
  data: '{"message": "Hello world!"}'
  sink:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: service
      name: event-display

Create the ping source:
```
$ oc apply -f <filename>
```

Check that the controller is mapped correctly by entering the following command:

$ oc get pingsource.sources.knative.dev <ping_source_name> -oyaml

Example output

apiVersion: sources.knative.dev/v1
kind: PingSource
metadata:
  annotations:
    sources.knative.dev/creator: developer
    sources.knative.dev/lastModifier: developer
  creationTimestamp: "2020-04-07T16:11:14Z"
  generation: 1
  name: test-ping-source
  namespace: default
  resourceVersion: "55257"
  selfLink: /apis/sources.knative.dev/v1/namespaces/default/pingsources/test-ping-source
  uid: 3d80d50b-f8c7-4c1b-99f7-3ec00e0a8164
spec:
  data: '{ value: "hello" }'
  schedule: '*/2 * * * *'
  sink:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: service
      name: event-display
      namespace: default

Verification

You can verify that the Kubernetes events were sent to the Knative event sink by looking at the sink pod’s logs.

By default, Knative services terminate their pods if no traffic is received within a 60 second period. The example shown in this guide creates a PingSource that sends a message every 2 minutes, so each message should be observed in a newly created pod.

Watch for new pods created:
```
$ watch oc get pods
```

Cancel watching the pods using Ctrl+C, then look at the logs of the created pod:

$ oc logs $(oc get pod -o name | grep event-display) -c user-container

Example output

☁️  cloudevents.Event
Validation: valid
Context Attributes,
  specversion: 1.0
  type: dev.knative.sources.ping
  source: /apis/v1/namespaces/default/pingsources/test-ping-source
  id: 042ff529-240e-45ee-b40c-3a908129853e
  time: 2020-04-07T16:22:00.000791674Z
  datacontenttype: application/json
Data,
  {
    "message": "Hello world!"
  }

Deleting the ping source

Delete the ping source:

$ oc delete -f <filename>

Example command

$ oc delete -f ping-source.yaml