We use analytics and cookies to understand site traffic. Information about your use of our site is shared with Google for that purpose. Learn more.
Sink binding
The SinkBinding
custom object supports decoupling event production from delivery addressing.
You can use sink binding to connect Kubernetes resources that embed a PodSpec
and want to produce events, such as an event source, to an addressable Kubernetes object that can receive events, also known as an event sink.
Sink binding can be used to create new event sources using any of the familiar compute objects that Kubernetes makes available.
For example, Deployment
, Job
, DaemonSet
, or StatefulSet
objects, or Knative abstractions, such as Service
or Configuration
objects, can be used.
Sink binding injects environment variables into the PodTemplateSpec
of the event sink, so that the application code does not need to interact directly with the Kubernetes API to locate the event destination.
Sink binding operates in one of two modes; Inclusion
or Exclusion
.
You can set the mode by modifying the SINK_BINDING_SELECTION_MODE
of the eventing-webhook
deployment accordingly. The mode determines the default scope of the webhook.
By default, the webhook is set to exclusion
mode, which means that any namespace that does not have the label bindings.knative.dev/exclude: true
will be subject to mutation evalutation.
If SINK_BINDING_SELECTION_MODE
is set to inclusion
, only the resources in a namespace labelled with bindings.knative.dev/include: true
will be considered. In inclusion
mode, any SinkBinding resource created will automatically label the subject
namespace with bindings.knative.dev/include: true
for inclusion in the potential environment variable inclusions.
Getting started
The following procedures show how you can create a sink binding and connect it to a service and event source in your cluster.
Creating a namespace
Create a namespace called sinkbinding-example
:
kubectl create namespace sinkbinding-example
Creating a Knative service
Create a Knative service if you do not have an existing event sink that you want to connect to the sink binding.
Prerequisites
- You must have Knative Serving installed on your cluster.
- Optional: If you want to use
kn
commands with sink binding, you must install thekn
CLI.
Procedure
Create a Knative service:
kn service create hello --image gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/event_display --env RESPONSE="Hello Serverless!"
- Copy the sample YAML into a
service.yaml
file:apiVersion: serving.knative.dev/v1 kind: Service metadata: name: event-display spec: template: spec: containers: - image: gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/event_display
- Apply the file:
kubectl apply --filename service.yaml
Creating a cron job
Create a cron job if you do not have an existing event source that you want to connect to the sink binding.
Create a CronJob
object:
- Copy the sample YAML into a
cronjob.yaml
file:apiVersion: batch/v1 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 image: <FILL IN YOUR IMAGE HERE> 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 file:
kubectl apply --filename heartbeats-source.yaml
Cloning a sample heartbeat cron job
Knative event-contrib contains a sample heartbeats event source.
Prerequisites
- Ensure that
ko publish
is set up correctly:KO_DOCKER_REPO
must be set. For example,gcr.io/[gcloud-project]
ordocker.io/<username>
.- You must have authenticated with your
KO_DOCKER_REPO
.
Procedure
- Clone the
event-contib
repository:$ git clone -b "release-0.20" https://github.com/knative/eventing-contrib.git
- Build a heartbeats image, and publish the image to your image repository:
$ ko publish knative.dev/eventing-contrib/cmd/heartbeats
Creating a SinkBinding object
Create a SinkBinding
object that directs events from your cron job to the event sink.
Prerequisites
- You must have Knative Eventing installed on your cluster.
- Optional: If you want to use
kn
commands with sink binding, you must install thekn
CLI.
Procedure
Create a sink binding:
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"
- Copy the sample YAML into a
cronjob.yaml
file:apiVersion: sources.knative.dev/v1alpha1 kind: SinkBinding metadata: name: bind-heartbeat spec: subject: apiVersion: batch/v1 kind: Job selector: matchLabels: app: heartbeat-cron sink: ref: apiVersion: serving.knative.dev/v1 kind: Service name: event-display
- Apply the file:
kubectl apply --filename heartbeats-source.yaml
Verification steps
- Verify that a message was sent to the Knative eventing system by looking at the
event-display
service logs:kubectl logs -l serving.knative.dev/service=event-display -c user-container --since=10m
- Observe the 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:
kubectl delete namespace sinkbinding-example
Feedback
Was this page helpful?
Glad to hear it! Please tell us how we can improve.
Sorry to hear that. Please tell us how we can improve.