Create a SinkBinding¶

This topic describes how to create a SinkBinding object. SinkBinding resolves a sink as a URI, sets the URI in the environment variable K_SINK, and adds the URI to a subject using K_SINK. If the URI changes, SinkBinding updates the value of K_SINK.

In the following examples, the sink is a Knative Service and the subject is a CronJob. If you have an existing subject and sink, you can replace the examples with your own values.

Before you begin¶

Before you can create a SinkBinding object:

You must have Knative Eventing installed on your cluster.
Optional: If you want to use kn commands with SinkBinding, install the kn CLI.

Optional: Choose SinkBinding namespace selection behavior¶

The SinkBinding object operates in one of two modes: exclusion or inclusion.

The default mode is exclusion. In exclusion mode, SinkBinding behavior is enabled for the namespace by default. To disallow a namespace from being evaluated for mutation you must exclude it using the label bindings.knative.dev/exclude: true.

In inclusion mode, SinkBinding behavior is not enabled for the namespace. Before a namespace can be evaluated for mutation, you must explicitly include it using the label bindings.knative.dev/include: true.

To set the SinkBinding object to inclusion mode:

Change the value of SINK_BINDING_SELECTION_MODE from exclusion to inclusion by running:

kubectl -n knative-eventing set env deployments eventing-webhook --containers="eventing-webhook" SINK_BINDING_SELECTION_MODE=inclusion

To verify that SINK_BINDING_SELECTION_MODE is set as desired, run:

kubectl -n knative-eventing set env deployments eventing-webhook --containers="eventing-webhook" --list | grep SINK_BINDING

Create a namespace¶

If you do not have an existing namespace, create a namespace for the SinkBinding object:

kubectl create namespace <namespace>

Where <namespace> is the namespace that you want your SinkBinding to use. For example, sinkbinding-example.

Note

If you have selected inclusion mode, you must add the bindings.knative.dev/include: true label to the namespace to enable SinkBinding behavior.

Create a sink¶

The sink can be any addressable Kubernetes object that can receive events.

If you do not have an existing sink that you want to connect to the SinkBinding object, create a Knative service.

Note

To create a Knative service you must have Knative Serving installed on your cluster.

knYAML

Create a Knative service by running:

kn service create <app-name> --image <image-url>

Where:

<app-name> is the name of the application.
<image-url> is the URL of the image container.

For example:

$ kn service create event-display --image gcr.io/knative-releases/knative.dev/eventing/cmd/event_display

Create a YAML file for the Knative service using the following template:
```
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: <app-name>
spec:
  template:
    spec:
      containers:
        - image: <image-url>
```
Where:
- <app-name> is the name of the application. For example, event-display.
- <image-url> is the URL of the image container. For example, gcr.io/knative-releases/knative.dev/eventing/cmd/event_display.
Apply the YAML file by running the command:
```
kubectl apply -f <filename>.yaml
```
Where <filename> is the name of the file you created in the previous step.

Create a subject¶

The subject must be a PodSpecable resource. You can use any PodSpecable resource in your cluster, for example:

Deployment
Job
DaemonSet
StatefulSet
Service.serving.knative.dev

If you do not have an existing PodSpecable subject that you want to use, you can use the following sample to create a CronJob object as the subject. The following CronJob makes a single cloud event that targets K_SINK and adds any extra overrides given by CE_OVERRIDES.

Create a YAML file for the CronJob using the following example:

apiVersion: batch/v1
kind: CronJob
metadata:
  name: heartbeat-cron
spec:
  # Run every minute
  schedule: "*/1 * * * *"
  jobTemplate:
    metadata:
      labels:
        app: heartbeat-cron
    spec:
      template:
        spec:
          restartPolicy: Never
          containers:
            - name: single-heartbeat
              image: gcr.io/knative-nightly/knative.dev/eventing/cmd/heartbeats
              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

Apply the YAML file by running the command:
```
kubectl apply -f <filename>.yaml
```
Where <filename> is the name of the file you created in the previous step.