# Hello World - Python A simple web app written in Python that you can use to test knative eventing. It shows how to consume a [CloudEvent](https://cloudevents.io/) in Knative eventing, and optionally how to respond back with another CloudEvent in the http response, by adding the Cloud Eventing headers outlined in the Cloud Events standard definition. We will deploy the app as a [Kubernetes Deployment](https://kubernetes.io/docs/concepts/workloads/controllers/deployment/) along with a [Kubernetes Service](https://kubernetes.io/docs/concepts/services-networking/service/). However, you can also deploy the app as a [Knative Serving Service](https://knative.dev/docs/serving/). Do the following steps 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: ```bash # Clone the relevant branch version such as "release-0.13" git clone https://github.com/knative/docs.git knative-docs cd knative-docs/code-samples/eventing/helloworld/helloworld-python ``` ## Before you begin - A Kubernetes cluster with [Knative Eventing](https://knative.dev/docs/install/eventing/install-eventing-with-yaml) installed. - [Docker](https://www.docker.com) installed and running on your local machine, and a Docker Hub account configured (we'll use it for a container registry). ## Recreating the sample code 1. Create a new file named `helloworld.py` and paste the following code. This code creates a basic web server which listens on port 8080: ```python from flask import Flask, request, make_response import uuid app = Flask(__name__) @app.route('/', methods=['POST']) def hello_world(): app.logger.warning(request.data) # Respond with another event (optional) response = make_response({ "msg": "Hi from helloworld-python app!" }) response.headers["Ce-Id"] = str(uuid.uuid4()) response.headers["Ce-specversion"] = "0.3" response.headers["Ce-Source"] = "knative/eventing/samples/hello-world" response.headers["Ce-Type"] = "dev.knative.samples.hifromknative" return response if __name__ == '__main__': app.run(debug=True, host='0.0.0.0', port=8080) ``` 1. Add a `requirements.txt` file containing the following contents: ```bash Flask==2.0.3 ``` 1. In your project directory, create a file named `Dockerfile` and copy the following code block into it. For detailed instructions on dockerizing a Go app, see [Deploying Go servers with Docker](https://blog.golang.org/docker). ```docker FROM python:3.9-alpine COPY . /app WORKDIR /app RUN pip install -r requirements.txt EXPOSE 8080 ENTRYPOINT [ "python" ] CMD [ "helloworld.py" ] ``` 1. Create a new file, `sample-app.yaml` and copy the following service definition into the file. Make sure to replace `{username}` with your Docker Hub username. ```yaml # Namespace for sample application with eventing enabled apiVersion: v1 kind: Namespace metadata: name: knative-samples labels: eventing.knative.dev/injection: enabled --- # A default broker apiVersion: eventing.knative.dev/v1 kind: Broker metadata: name: default namespace: knative-samples annotations: # Note: you can set the eventing.knative.dev/broker.class annotation to change the class of the broker. # The default broker class is MTChannelBasedBroker, but Knative also supports use of the other class. eventing.knative.dev/broker.class: MTChannelBasedBroker spec: {} --- # Helloworld-python app deployment apiVersion: apps/v1 kind: Deployment metadata: name: helloworld-python namespace: knative-samples spec: replicas: 1 selector: matchLabels: &labels app: helloworld-python template: metadata: labels: *labels spec: containers: - name: helloworld-python image: docker.io/{username}/helloworld-python imagePullPolicy: IfNotPresent --- # Service that exposes helloworld-python app. # This will be the subscriber for the Trigger apiVersion: v1 kind: Service metadata: name: helloworld-python namespace: knative-samples spec: selector: app: helloworld-python ports: - protocol: TCP port: 80 targetPort: 8080 --- # Knative Eventing Trigger to trigger the helloworld-python service apiVersion: eventing.knative.dev/v1 kind: Trigger metadata: name: helloworld-python namespace: knative-samples spec: broker: default filter: attributes: type: dev.knative.samples.helloworld source: dev.knative.samples/helloworldsource subscriber: ref: apiVersion: v1 kind: Service name: helloworld-python ``` ## Building and deploying the sample Once you have recreated the sample code files (or used the files in the sample folder) you're ready to build and deploy the sample app. 1. Use Docker to build the sample code into a container. To build and push with Docker Hub, run these commands replacing `{username}` with your Docker Hub username: ```bash # Build and push the container on your local machine. docker buildx build --platform linux/arm64,linux/amd64 -t "{username}/helloworld-python" --push . ``` 1. After the build has completed and the container is pushed to Docker Hub, you can deploy the sample application into your cluster. Ensure that the container image value in `sample-app.yaml` matches the container you built in the previous step. Apply the configuration using `kubectl`: ```bash kubectl apply -f sample-app.yaml ``` 1. The previous command creates a namespace `knative-samples` and labels it with `knative-eventing-injection=enabled`, to enable eventing in the namespace. Verify using the following command: ```bash kubectl get ns knative-samples --show-labels ``` 1. It deployed the `helloworld-python` app as a K8s Deployment and created a K8s service names helloworld-python. Verify using the following command: ```bash kubectl --namespace knative-samples get deployments helloworld-python kubectl --namespace knative-samples get svc helloworld-python ``` 1. It created a Knative Eventing Trigger to route certain events to the helloworld-python application. Make sure that `Ready=true`: ```bash kubectl -n knative-samples get trigger helloworld-python ``` ## Send and verify CloudEvents After you have deployed the application, and have verified that the namespace, sample application and trigger are ready, you can send a CloudEvent. ### Send CloudEvent to the Broker You can send an HTTP request directly to the Knative [Broker](https://knative.dev/docs/eventing/broker/) if the correct CloudEvent headers are set. 1. Deploy a curl pod and SSH into it: ```bash kubectl --namespace knative-samples run curl --image=radial/busyboxplus:curl -it ``` 1. Run the following command in the SSH terminal: ```bash curl -v "broker-ingress.knative-eventing.svc.cluster.local/knative-samples/default" \ -X POST \ -H "Ce-Id: 536808d3-88be-4077-9d7a-a3f162705f79" \ -H "Ce-specversion: 0.3" \ -H "Ce-Type: dev.knative.samples.helloworld" \ -H "Ce-Source: dev.knative.samples/helloworldsource" \ -H "Content-Type: application/json" \ -d '{"msg":"Hello World from the curl pod."}' exit ``` ### Verify that event is received by helloworld-python app The Helloworld-python app logs the context and the msg of the event you created earlier, and replies with another event. 1. Display helloworld-python app logs ```bash kubectl --namespace knative-samples logs -l app=helloworld-python --tail=50 ``` You should see something similar to: ```{ .bash .no-copy } Event received. Context: Context Attributes, specversion: 0.3 type: dev.knative.samples.helloworld source: dev.knative.samples/helloworldsource id: 536808d3-88be-4077-9d7a-a3f162705f79 time: 2019-10-04T22:35:26.05871736Z datacontenttype: application/json Extensions, knativearrivaltime: 2019-10-04T22:35:26Z knativehistory: default-kn2-trigger-kn-channel.knative-samples.svc.cluster.local traceparent: 00-971d4644229653483d38c46e92a959c7-92c66312e4bb39be-00 Hello World Message "Hello World from the curl pod." Responded with event Validation: valid Context Attributes, specversion: 0.2 type: dev.knative.samples.hifromknative source: knative/eventing/samples/hello-world id: 37458d77-01f5-411e-a243-a459bbf79682 Data, {"msg":"Hi from Knative!"} ``` Try the CloudEvent attributes in the curl command and the trigger specification to understand how [Triggers](https://knative.dev/docs/eventing/broker/triggers/) work. ## Verify reply from helloworld-python app The `helloworld-python` app replies with an event type `type= dev.knative.samples.hifromknative`, and source `source=knative/eventing/samples/hello-world`. The event enters the eventing mesh through the broker, and can be delivered to event sinks using a trigger 1. Deploy a Pod that receives any CloudEvent and logs the event to its output. 1. Copy the following YAML into a file: ```yaml # event-display app deploment apiVersion: apps/v1 kind: Deployment metadata: name: event-display namespace: knative-samples spec: replicas: 1 selector: matchLabels: &labels app: event-display template: metadata: labels: *labels spec: containers: - name: helloworld-python image: gcr.io/knative-releases/knative.dev/eventing/cmd/event_display --- # Service that exposes event-display app. # This will be the subscriber for the Trigger kind: Service apiVersion: v1 metadata: name: event-display namespace: knative-samples spec: selector: app: event-display ports: - protocol: TCP port: 80 targetPort: 8080 ``` 1. Apply the YAML file by running the command: ```bash kubectl apply -f .yaml ``` Where `` is the name of the file you created in the previous step. 1. Create a trigger to deliver the event to the previously created service. 1. Copy the following YAML into a file: ```yaml apiVersion: eventing.knative.dev/v1 kind: Trigger metadata: name: event-display namespace: knative-samples spec: broker: default filter: attributes: type: dev.knative.samples.hifromknative source: knative/eventing/samples/hello-world subscriber: ref: apiVersion: v1 kind: Service name: event-display ``` 1. Apply the YAML file by running the command: ```bash kubectl apply -f .yaml ``` Where `` is the name of the file you created in the previous step. 1. [Send a CloudEvent to the Broker](#send-and-verify-cloudevents) 1. Check the logs of `event-display` Service: ```bash kubectl -n knative-samples logs -l app=event-display --tail=50 ``` Example output: ```{ .bash .no-copy } cloudevents.Event Validation: valid Context Attributes, specversion: 0.3 type: dev.knative.samples.hifromknative source: knative/eventing/samples/hello-world id: 8a7384b9-8bbe-4634-bf0f-ead07e450b2a time: 2019-10-04T22:53:39.844943931Z datacontenttype: application/json Extensions, knativearrivaltime: 2019-10-04T22:53:39Z knativehistory: default-kn2-ingress-kn-channel.knative-samples.svc.cluster.local traceparent: 00-4b01db030b9ea04bb150b77c8fa86509-2740816590a7604f-00 Data, { "msg": "Hi from helloworld- app!" } ``` ## Removing the sample app deployment To remove the sample app from your cluster, delete the service record: ```bash kubectl delete -f sample-app.yaml ```