kn-py-cloudevent-transformation-function

Example Knative Python function for receiving a custom json event (payload) which will be transformed into a CloudEvent.

How the function works

The function starts a HTTP server, transforms an incoming json payload to a CloudEvent and sends it to the configured K_SINK (injected via a Knative SinkBinding).

The webhook endpoint in the function, i.e. the HTTP POST target, by default is /webhook (configurable.)

See the deployment section for configuration options and details.

The event transformation is done as follows:

CloudEvent Field	Event Field	Comment	Example
ID	tbd	An ID specified in UUIDv4 format	0866ff41-0d90-4003-a0a6-06b4c0d16cfa
Source	tbd	The source is fixed in this version.	/kn-py-cloudevent-transformation-function
Type	type	Event type field is lower-cased and injected into a fixed CloudEvent Type format (my.very.own.cloudevent."f"{payload['action']}.v0)	my.very.own.cloudevent.created.v0
Time	time	Systemtime	2023-09-11T13:26:37.469567Z
Data	tbd	JSON-encoded data event

A full example of a structured CloudEvent (JSON):

{
	"action": "created",
	"example": {
	  "attendee": {
		"feelings": "EXCITED"
	  }
	},
	"actuator": {
	  "event": {
		"organization": "Container Days 2023"
	  }
	},
	"next": {
		"up": "Coffee Break - W00t"
	},
	"command_id": "0866ff41-0d90-4003-a0a6-06b4c0d16cfa"
}

Step 1 - Build

Buildpacks are used to create the container image.

Create the container image locally to test your function logic. Change the IMAGE name accordingly, example below for Docker.

export IMAGE=<docker username>/kn-py-cloudevent-transformation-function:1.0
pack build -B gcr.io/buildpacks/builder:v1 ${IMAGE}

Step 2 - Test

Verify the container image works by executing it locally.

Change into the test directory

cd test

Start the container image by running the following command:

docker run -e PORT=8080 --env-file docker-test-env-variable -it --rm -p 8080:8080 ${IMAGE}

You should see output similar to the following:

 * Serving Flask app 'handler.py'
 * Debug mode: off
2023-07-24 11:02:33,324 INFO werkzeug MainThread : WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.
 * Running on all addresses (0.0.0.0)
 * Running on http://127.0.0.1:8080
 * Running on http://172.17.0.3:8080
2023-07-24 11:02:33,324 INFO werkzeug MainThread : Press CTRL+C to quit

docker ps -a

CONTAINER ID   IMAGE                                                                        COMMAND                  CREATED          STATUS                   PORTS                                                NAMES
eca1a2f27ef0   rguske/kn-py-cloudevent-transformation-function:1.0   "/cnb/process/web"       10 seconds ago   Up 9 seconds             0.0.0.0:8080->8080/tcp                               lucid_boyd

Step 2 - Test

In a separate terminal window, go to the test directory and use the `test-payload.json`` file to validate the function is working.

Send the json payload to the webhook endpoint. The following json blob will be used as a simulated test-event:

cat test-payload.json

{
	"action": "created",
	"example": {
	  "attendee": {
		"feelings": "EXCITED"
	  }
	},
	"actuator": {
	  "event": {
		"organization": "Container Days 2023"
	  }
	},
	"next": {
		"up": "Coffee Break - W00t"
	},

	"command_id": "0866ff41-0d90-4003-a0a6-06b4c0d16cfa"
  }

Send the json payload to the /webhook endpoint:

curl -s -d@test-payload.json http://127.0.0.1:8080/webhook -H 'Content-Type: application/json'

You should see an output like:

{'specversion': '1.0', 'type': 'my.very.own.cloudevent.created.v0', 'datacontenttype': 'application/json', 'source': '/kn-py-cloudevent-transformation-function', 'id': '0866ff41-0d90-4003-a0a6-06b4c0d16cfa', 'time': '2023-09-11T11:02:39.283277Z', 'data': ......}}
2023-09-11 11:02:39,290 INFO werkzeug Thread-1 (process_request_thread) : 172.17.0.1 - - [24/Jul/2023 11:02:39] "POST /webhook HTTP/1.1" 500 -

The http 500 error is expected since the transformed json blob couldn't be send to a K_SINK. Important in this local test, is the transformed event.

Step 3 - Deploy

⚠️ The following steps assume a working Knative environment using the rabbitmq-broker or the MTChannelBasedBroker. The Knative service and sinkbinding will be installed in the vmware-functions Kubernetes namespace, assuming that the broker is also available there.

Deploy the Function

Create the SinkBinding which will automatically inject the Knative broker into the function.

kubectl create -f sinkbinding.yaml -n vmware-functions

Deploy the function to Knative:

kubectl create -f function.yaml -n vmware-functions

For testing purposes, the Knative manifest contains the following annotations, which will ensure the Knative Service Pod will always run exactly one instance for debugging purposes.

annotations:
  autoscaling.knative.dev/maxScale: "1"
  autoscaling.knative.dev/minScale: "1"

Step 4 - Undeploy

# undeploy function
kubectl delete -f function.yaml -n vmware-functions

# undeploy sinkbinding
kubectl delete -f sinkbinding.yaml -n vmware-functions

# delete secret
kubectl delete secret webhook-auth -n vmware-functions