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Using a ping source

A ping source is 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, as shown in the example:

Example ping source
apiVersion: sources.knative.dev/v1alpha2
kind: PingSource
metadata:
  name: test-ping-source
spec:
  schedule: "*/2 * * * *" (1)
  jsonData: '{"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.

Creating a ping source using the Knative CLI

The following sections describe how to create, verify and remove a basic PingSource object using the kn CLI.

Prerequisites

  • You have Knative Serving and Eventing installed.

  • You have the kn CLI installed.

Procedure

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

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

  2. For each set of ping events that you want to request, create a PingSource object 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

  3. 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 PingSource object that sends a message every 2 minutes, so each message should be observed in a newly created pod.

  1. Watch for new pods created:

    $ watch oc get pods

  2. 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!"
  }

Remove the ping source

  1. Delete the PingSource object:

    $ kn delete pingsources.sources.knative.dev test-ping-source

  2. Delete the event-display service:

    $ kn delete service.serving.knative.dev event-display

Creating a ping source using YAML files

The following sections describe how to create, verify and remove a basic ping source using YAML files.

Prerequisites

  • You have Knative Serving and Eventing installed.

The following procedure requires you to create YAML files.

If you change the names of the YAML files from those used in the examples, you must ensure that you also update the corresponding CLI commands.
Procedure

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

    1. Copy the example YAML into a file named service.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

    2. Apply the service.yaml file:

      $ oc apply --filename service.yaml

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

    1. Copy the example YAML into a file named ping-source.yaml:

      apiVersion: sources.knative.dev/v1alpha2
kind: PingSource
metadata:
  name: test-ping-source
spec:
  schedule: "*/2 * * * *"
  jsonData: '{"message": "Hello world!"}'
  sink:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: event-display

    2. Apply the ping-source.yaml file:

      $ oc apply --filename ping-source.yaml

  3. Check that the controller is mapped correctly by entering the following command and observing the output:

    $ oc get pingsource.sources.knative.dev test-ping-source -oyaml
    Example output
    apiVersion: sources.knative.dev/v1alpha2
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/v1alpha2/namespaces/default/pingsources/test-ping-source
  uid: 3d80d50b-f8c7-4c1b-99f7-3ec00e0a8164
spec:
  jsonData: '{ 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 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 PingSource object that sends a message every 2 minutes, so each message should be observed in a newly created pod.

  1. Watch for new pods created:

    $ watch oc get pods

  2. 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!"
  }

Remove the PingSource

  1. Delete the service by entering the following command:

    $ oc delete --filename service.yaml

  2. Delete the PingSource object by entering the following command:

    $ oc delete --filename ping-source.yaml