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Added Python Example for Knative Eventing (#2299) 

* Added Python Knative Eventing Helloworld Example

* Update docs/eventing/samples/helloworld/helloworld-python/Dockerfile

Co-Authored-By: Matt Moore <mattmoor@vmware.com>

* Update docs/eventing/samples/helloworld/helloworld-python/Dockerfile

Co-Authored-By: Matt Moore <mattmoor@vmware.com>

* Update docs/eventing/samples/helloworld/helloworld-python/README.md

Co-Authored-By: Matt Moore <mattmoor@vmware.com>

* Apply suggestions from code review

Co-Authored-By: Matt Moore <mattmoor@vmware.com>

Co-authored-by: Matt Moore <mattmoor@vmware.com>
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FROM python:alpine3.7
COPY . /app
WORKDIR /app
RUN pip install -r requirements.txt
EXPOSE 8080
ENTRYPOINT [ "python" ]
CMD [ "helloworld.py" ]

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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](../../../../serving/README.md).
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:
```shell
# Clone the relevant branch version such as "release-0.13"
git clone -b "{{< branch >}}" https://github.com/knative/docs knative-docs
cd knative-docs/docs/eventing/samples/helloworld/helloworld-python
```
## Before you begin
- A Kubernetes cluster with [Knative Eventing](../../../getting-started.md#installing-knative-eventing) 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==1.1.1
```
1. In your project directory, create a file named `Dockerfile` and copy the code
block below into it. For detailed instructions on dockerizing a Go app, see
[Deploying Go servers with Docker](https://blog.golang.org/docker).
```docker
FROM python:alpine3.7
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:
knative-eventing-injection: enabled
---
# Helloworld-python app deploment
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
kind: Service
apiVersion: v1
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/v1alpha1
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:
```shell
# Build the container on your local machine
docker build -t {username}/helloworld-python .
# Push the container to docker registry
docker push {username}/helloworld-python
```
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`:
```shell
kubectl apply --filename sample-app.yaml
```
1. Above command created a namespace `knative-samples` and labelled it with `knative-eventing-injection=enabled`, to enable eventing in the namespace. Verify using the following command:
```shell
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.
```shell
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
```shell
kubectl --namespace knative-samples get trigger helloworld-python
```
## Send and verify CloudEvents
Once you have deployed the application and verified that the namespace, sample application and trigger are ready, let's send a CloudEvent.
### Send CloudEvent to the Broker
We can send an http request directly to the [Broker](../../../broker-trigger.md) with correct CloudEvent headers set.
1. Deploy a curl pod and SSH into it
```shell
kubectl --namespace knative-samples run curl --image=radial/busyboxplus:curl -it
```
1. Run the following in the SSH terminal
```shell
curl -v "default-broker.knative-samples.svc.cluster.local" \
-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
Helloworld-python app logs the context and the msg of the above event, and replies back with another event.
1. Display helloworld-python app logs
```shell
kubectl --namespace knative-samples logs -l app=helloworld-python --tail=50
```
You should see something similar to:
```shell
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!"}
```
Play around with the CloudEvent attributes in the curl command and the trigger specification to understand how [Triggers work](../../../broker-trigger.md#trigger).
## Verify reply from helloworld-python app
`helloworld-python` app replies back with an event of `type= dev.knative.samples.hifromknative`, and `source=knative/eventing/samples/hello-world`. This event enters the eventing mesh via the Broker and can be delivered to other services using a Trigger
1. Deploy a pod that receives any CloudEvent and logs the event to its output.
```shell
kubectl --namespace knative-samples apply --filename - << END
# 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/github.com/knative/eventing-sources/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
END
```
1. Create a trigger to deliver the event to the above service
```shell
kubectl --namespace knative-samples apply --filename - << END
apiVersion: eventing.knative.dev/v1alpha1
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
END
```
1. [Send a CloudEvent to the Broker](###Send-CloudEvent-to-the-Broker)
1. Check the logs of event-display service
```shell
kubectl --namespace knative-samples logs -l app=event-display --tail=50
```
You should see something similar to:
```shell
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!"
}
```
**Note: You could use the above approach to test your applications too.**
## Removing the sample app deployment
To remove the sample app from your cluster, delete the service record:
```shell
kubectl delete --filename sample-app.yaml
```

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---
title: "Hello World - Python"
linkTitle: "Python"
weight: 20
type: "docs"
---
{{% readfile file="README.md" %}}

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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)

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Flask==1.1.1

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# Namespace for sample application with eventing enabled
apiVersion: v1
kind: Namespace
metadata:
name: knative-samples
labels:
knative-eventing-injection: enabled
---
# Helloworld-go app deploment
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/axsauze/helloworld-python
imagePullPolicy: IfNotPresent
---
# Service that exposes helloworld-go app.
# This will be the subscriber for the Trigger
kind: Service
apiVersion: v1
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-go service
apiVersion: eventing.knative.dev/v1alpha1
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