Cloud Events - Node.js

A simple web app written in Node.js that can receive and send Cloud Events that you can use for testing. It supports running in two modes:

  1. The default mode has the app reply to your input events with the output event, which is simplest for demonstrating things working in isolation, but is also the model for working for the Knative Eventing Broker concept.

  2. K_SINK mode has the app send events to the destination encoded in $K_SINK, which is useful to demonstrate how folks can synthesize events to send to a Service or Broker when not initiated by a Broker invocation (e.g. implementing an event source)

The application will use $K_SINK-mode whenever the environment variable is specified.

Follow the steps below to create the sample code and then deploy the app to your cluster. You can also download a working copy of the sample, by running the following commands:

git clone -b "main" knative-docs
cd knative-docs/docs/serving/samples/cloudevents/cloudevents-nodejs

Before you begin

  • A Kubernetes cluster with Knative installed and DNS configured. Follow the installation instructions if you need to create one.
  • Docker installed and running on your local machine, and a Docker Hub account configured (we’ll use it for a container registry).

The Sample Code

In the index.js file, you will see two key functions for the different modes of operation:

const receiveAndSend = (cloudEvent, res) => {
  // This is called whenever an event is received if $K_SINK is set, and sends a new event
  // to the url in $K_SINK.

const receiveAndReply = (cloudEvent, res) => {
  // This is called whenever an event is received if $K_SINK is NOT set, and it replies with
  // the new event instead.

Build and Deploy the Application

In the Dockerfile, you can see how the dependencies are installed using npm. You can build and push this to your registry of choice via:

docker build -t <image> .
docker push <image>

To deploy the Knative service, edit the service.yaml file and replace <registry/repository/image:tag> with the image you have just created.

kubectl apply -f service.yaml

To deploy using the kn CLI:

kn service create cloudevents-nodejs --image=<image>

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Testing the sample

Get the URL for your Service with:

$ kubectl get ksvc
NAME                 URL                                                LATESTCREATED              LATESTREADY                READY   REASON
cloudevents-nodejs   cloudevents-nodejs-ss5pj   cloudevents-nodejs-ss5pj   True

Then send a cloud event to it with:

$ curl -X POST \
    -H "content-type: application/json"  \
    -H "ce-specversion: 1.0"  \
    -H "ce-source: curl-command"  \
    -H "ce-type: curl.demo"  \
    -H "ce-id: 123-abc"  \
    -d '{"name":"Dave"}' \

You will get back:

{"message":"Hello, Dave"}

Removing the sample app deployment

To remove the sample app from your cluster, delete the service.

kubectl delete --filename service.yaml
kn service delete cloudevents-nodejs

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