Cloud Events - Go

A simple web app written in Go 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" https://github.com/knative/docs knative-docs
cd knative-docs/docs/serving/samples/cloudevents/cloudevents-go

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.

  1. If you look in cloudevents.go, you will see two key functions for the different modes of operation:

    func (recv *Receiver) ReceiveAndSend(ctx context.Context, event cloudevents.Event) cloudevents.Result {
  // This is called whenever an event is received if $K_SINK is set, and sends a new event
  // to the url in $K_SINK.
}

func (recv *Receiver) ReceiveAndReply(ctx context.Context, event cloudevents.Event)  (*cloudevents.Event, cloudevents.Result) {
  // This is called whenever an event is received if $K_SINK is NOT set, and it replies with
  // the new event instead.
}

  2. Choose how you would like to build the application:

    If you look in Dockerfile, you will see a method for pulling in the dependencies and building a small Go container based on Alpine. You can build and push this to your registry of choice via:

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

    You can use ko to build and push just the image with:

    ko publish github.com/knative/docs/docs/serving/samples/cloudevents/cloudevents-go

    However, if you use ko for the next step, this is not necessary.

  3. Choose how you would like to deploy the application:

    If you look in service.yaml, take the <image> name above and insert it into the image: field, then run:

    kubectl apply -f service.yaml

    If using ko to build and push:

    ko apply -f service.yaml

    If using kn to deploy:

    kn service create cloudevents-go --image=<IMAGE>

    You can compose kn and ko to build and deploy with a single step using:

    kn service create cloudevents-go --image=$(ko publish github.com/knative/docs/docs/serving/samples/cloudevents/cloudevents-go)

Testing the sample

Get the URL for your Service with:

$ kubectl get ksvc
NAME             URL                                            LATESTCREATED          LATESTREADY            READY   REASON
cloudevents-go   http://cloudevents-go.default.1.2.3.4.xip.io   cloudevents-go-ss5pj   cloudevents-go-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"}' \
    http://cloudevents-go.default.1.2.3.4.xip.io

You will get back:

{"message":"Hello, Dave"}

Removing the sample app deployment

To remove the sample app from your cluster, delete the service record:

kubectl delete --filename service.yaml