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Sink Binding Example
A SinkBinding is responsible for linking together “addressable” Kubernetes
resources that may receive events (aka the event “sink”) with Kubernetes
resources that embed a PodSpec (as spec.template.spec
) and want to produce
events.
The SinkBinding can be used to author new event sources using any of the familiar compute abstractions that Kubernetes makes available (e.g. Deployment, Job, DaemonSet, StatefulSet), or Knative abstractions (e.g. Service, Configuration).
Create a CronJob that uses SinkBinding
Prerequisites
- Setup Knative Serving.
- Setup Knative Eventing and Sources.
Prepare the heartbeats image
Knative event-contrib has a sample of heartbeats event source. You could clone the source codes by
git clone -b "{{< branch >}}" 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
Note: ko publish
requires:
KO_DOCKER_REPO
to be set. (e.g.gcr.io/[gcloud-project]
ordocker.io/<username>
)- you to be authenticated with your
KO_DOCKER_REPO
Creating our event sink
In order to verify our SinkBinding
is working, we will create an Event Display
Service that dumps incoming messages to its log.
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
Use following command to create the service from service.yaml
:
kubectl apply --filename service.yaml
The status of the created service can be seen using:
kubectl get ksvc
NAME URL LATESTCREATED LATESTREADY READY REASON
event-display http://event-display.default.1.2.3.4.xip.io event-display-gqjbw event-display-gqjbw True
Create our 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
:
apiVersion: sources.knative.dev/v1
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
ceOverrides:
extensions:
sink: bound
In this case, we will bind any Job
with the labels app: heartbeat-cron
.
Use the following command to create the event source from sinkbinding.yaml
:
kubectl apply --filename sinkbinding.yaml
Create our CronJob
Now we will use the heartbeats container to send events to $K_SINK
every time
the CronJob runs:
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
First, edit heartbeats-source.yaml
to include the image name from the
ko publish
command above, then run the following to apply it:
kubectl apply --filename heartbeats-source.yaml
Verify
We will verify that the message was sent to the Knative eventing system by looking at event-display service logs.
kubectl logs -l serving.knative.dev/service=event-display -c user-container --since=10m
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": ""
}
Using the SinkBinding with a Knative Service
SinkBinding is also compatible with our Knative Serving Cloud Events
samples; as a next step try using those
together. For example, the cloudevents-go
sample may be bound with:
apiVersion: sources.knative.dev/v1
kind: SinkBinding
metadata:
name: bind-heartbeat
spec:
subject:
apiVersion: serving.knative.dev/v1
kind: Service
name: cloudevents-go
sink:
ref:
apiVersion: serving.knative.dev/v1
kind: Service
name: event-display
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