SinkBinding

A SinkBinding provides a framework for injecting K_SINK (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).

Prerequisites

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

Installation

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

Example

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

git clone -b "release-0.17" https://github.com/knative/eventing-contrib.git

And then build a heartbeats image and publish to your image repo with

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

Creating a namespace

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

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:

kubectl -n sinkbinding-example apply -f - << EOF
apiVersion: apps/v1
kind: Deployment
metadata:
  name: event-display
spec:
  replicas: 1
  selector:
    matchLabels: &labels
      app: event-display
  template:
    metadata:
      labels: *labels
    spec:
      containers:
        - name: event-display
          image: gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/event_display
---
kind: Service
apiVersion: v1
metadata:
  name: event-display
spec:
  selector:
    app: event-display
  ports:
  - protocol: TCP
    port: 80
    targetPort: 8080
EOF

Creating the SinkBinding

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:

• YAML
• kn

kubectl -n sinkbinding-example apply -f - << EOF
apiVersion: sources.knative.dev/v1beta1
kind: SinkBinding
metadata:
  name: bind-heartbeat
spec:
  subject:
    apiVersion: batch/v1
    kind: Job
    selector:
      matchLabels:
        app: heartbeat-cron
  sink:
    ref:
      apiVersion: v1
      kind: Service
      name: event-display
  ceOverrides:
    extensions:
      sink: bound
EOF

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

In this case, we will bind any Job with the labels app: heartbeat-cron.

Creating the CronJob

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

kubectl -n sinkbinding-example apply -f - << EOF
apiVersion: batch/v1beta1
kind: CronJob
metadata:
  name: heartbeat-cron
spec:
  # Run every minute
  schedule: "* * * * *"
  jobTemplate:
    metadata:
      labels:
        app: heartbeat-cron
    spec:
      template:
        spec:
          restartPolicy: Never
          containers:
            - name: single-heartbeat
              # This corresponds to a heartbeats image uri you build and publish in the previous step
              # e.g. gcr.io/[gcloud-project]/knative.dev/eventing-contrib/cmd/heartbeats
              image: <heartbeats_image_uri>
              args:
                - --period=1
              env:
                - name: ONE_SHOT
                  value: "true"
                - name: POD_NAME
                  valueFrom:
                    fieldRef:
                      fieldPath: metadata.name
                - name: POD_NAMESPACE
                  valueFrom:
                    fieldRef:
                      fieldPath: metadata.namespace
EOF

Verify

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

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:

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

Cleanup

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

kubectl delete namespace sinkbinding-example

Reference Documentation

See the SinkBinding specification.

Contact

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