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Cloud Pub/Sub triggered service

In this sample, we'll take a look at how to connect GCP Pub/Sub messages to a service with Knative Eventing. We'll roughly be following CloudPubSubSource Example docs page.

Knative with GCP & PubSub Topic

We're assuming that you already went through Install Knative with GCP section of the setup.

Create a Pub/Sub topic

Create a Pub/Sub topic where messages will be sent:

gcloud pubsub topics create testing

CloudPubSubSource

Create a CloudPubSubSource to connect PubSub messages to Knative Eventing. The default cloudpubsubsource.yaml connects Pub/Sub messages to a service directly.

Instead, use the following cloudpubsubsource.yaml to connect Pub/Sub messages to a Broker, so, we can have multiple triggers to invoke multiple services on the same message.

Note that there's an alternative cloudpubsubsource-workload.yaml. Use this version instead if you setup workload identity on GKE.

Create the CloudPubSubSource:

kubectl apply -f cloudpubsubsource.yaml

Broker

Make sure there's a Broker in the default namespace by following instructions in Broker Creation page.

Consumer

For the event consumer, we can use the Event Display service defined in kservice.yaml.

Create the service:

kubectl apply -f kservice.yaml

Trigger

Connect the Event Display service to the Broker with a Trigger defined in trigger.yaml:

kubectl apply -f trigger.yaml

Check that the trigger is ready:

kubectl get trigger

NAME                           READY   REASON   BROKER    SUBSCRIBER_URI                                   AGE
trigger-event-display-pubsub   True             default   http://event-display.default.svc.cluster.local   95s

Test the service

We can now test our service by sending a message to Pub/Sub topic:

gcloud pubsub topics publish testing --message="Hello World"

messageIds:
- '198012587785403'

Wait a little and check that a pod is created:

kubectl get pods

Inspect the logs of the pod (replace <podid> with actual pod id):

kubectl logs <podid> -c user-container --follow

You should see something similar to this:

info: event_display.Startup[0]
      Received CloudEvent
      ID: 1203138894276445
      Source: //pubsub.googleapis.com/projects/knative-atamel/topics/testing
      Type: com.google.cloud.pubsub.topic.publish
      Subject:
      DataSchema:
      DataContentType: application/json
      Time: 2020-05-13T14:57:20.106Z
      SpecVersion: V1_0
      Data: {"subscription":"cre-pull-b1d2ed86-d4ed-4cea-919e-39895b1f818d","message":{"messageId":"1203138894276445","data":"SGVsbG8gV29ybGQ=","publishTime":"2020-05-13T14:57:20.106Z"}}