SinkBinding

A SinkBinding provides a framework for injecting (destination address) and K_CE_OVERRIDES (JSON cloudevents attributes) environment variables into any Kubernetes resource which has a spec.template that looks like a Pod (aka PodSpecable).

  • Install
  • Set KO_DOCKER_REPO (e.g. gcr.io/[gcloud-project] or docker.io/<username>)
  • Authenticated with your KO_DOCKER_REPO
  • Install docker

The SinkBinding type is enabled by default when you install Knative Eventing.

This example shows the SinkBinding that injects$K_SINK and $K_CE_OVERRIDES into select Jobs and direct events to the Event Display Service.

Prepare the heartbeats image

Knative event-sources has a sample of heartbeats event source. You could clone the source codes by

  1. ko publish knative.dev/eventing-contrib/cmd/heartbeats

Create a new namespace called sinkbinding-example by entering the following command:

  1. kubectl create namespace sinkbinding-example

Creating the Event Display Service

In this step, you create one event consumer, event-display to verify that SinkBinding is properly working.

To deploy the event-display consumer to your cluster, run the following command:

In order to direct events to our Event Display, we will first create a SinkBinding that will inject $K_SINK and $K_CE_OVERRIDES into select Jobs:

  1. kubectl -n sinkbinding-example apply -f - << EOF
  2. kind: SinkBinding
  4.   name: bind-heartbeat
  5. spec:
  6.   subject:
  7.     apiVersion: batch/v1
  8.     kind: Job
  9.     selector:
  10.       matchLabels:
  11.         app: heartbeat-cron
  13.   sink:
  14.     ref:
  15.       apiVersion: v1
  16.       kind: Service
  17.       name: event-display
  18.   ceOverrides:
  19.     extensions:
  20.       sink: bound
  21. EOF
  1. kn source binding create bind-heartbeat \
  2.   --subject "Job:batch/v1:app=heartbeat-cron" \
  3.   --sink http://event-display.svc.cluster.local \

Creating the CronJob

Now we will use the heartbeats container to send events to $K_SINK every time the CronJob runs:

View the logs for the event-display event consumer by entering the following command:

  1. kubectl -n sinkbinding-example logs -l app=event-display --tail=200

You should see log lines showing the request headers and body of the event message sent by the heartbeats source to the display function:

  1. ☁️  cloudevents.Event
  2. Validation: valid
  3. Context Attributes,
  4.   specversion: 1.0
  5.   type: dev.knative.eventing.samples.heartbeat
  6.   source: https://knative.dev/eventing-contrib/cmd/heartbeats/#default/heartbeat-cron-1582120020-75qrz
  7.   id: 5f4122be-ac6f-4349-a94f-4bfc6eb3f687
  8.   time: 2020-02-19T13:47:10.41428688Z
  9.   datacontenttype: application/json
  10. Extensions,
  11.   beats: true
  12.   heart: yes
  13.   the: 42
  14. Data,
  15.   {
  16.     "id": 1,
  17.     "label": ""

Cleanup

Delete the sinkbinding-example namespace and all of its resources from your cluster by entering the following command:

For any inquiries about this source, please reach out on to the Knative users group.