docs/serving/samples/helloworld-python

Hello World - Python sample

This sample application shows how to create a hello world application in Python. When called, this application reads an env variable 'TARGET' and prints "Hello World: ${TARGET}!". If TARGET is not specified, it will use "NOT SPECIFIED" as the TARGET.

Prerequisites

• You have a Kubernetes cluster with Knative installed. Follow the installation instructions if you need to do this.
• You have installed and initialized Google Cloud SDK and have created a project in Google Cloud.
• You have kubectl configured to connect to the Kubernetes cluster running Knative.

Steps to recreate the sample code

While you can clone all of the code from this directory, hello world apps are generally more useful if you build them step-by-step. The following instructions recreate the source files from this folder.

1. Create a new directory and cd into it:

   mkdir app
   cd app
   

2. Create a file named app.py and copy the code block below into it:

   import os
   
   from flask import Flask
   
   app = Flask(__name__)
   
   @app.route('/')
   def hello_world():
       target = os.environ.get('TARGET', 'NOT SPECIFIED')
       return 'Hello World: {}!\n'.format(target)
   
   if __name__ == "__main__":
       app.run(debug=True,host='0.0.0.0',port=8080)
   

3. Create a file named Dockerfile and copy the code block below into it. See official Python docker image for more details.

   FROM python
   
   ENV APP_HOME /app
   COPY . $APP_HOME
   WORKDIR $APP_HOME
   
   RUN pip install Flask
   
   ENTRYPOINT ["python"]
   CMD ["app.py"]
   

4. Create a file named service.yaml and copy the following service definition into the file. Make sure to replace {PROJECT_ID} with the ID of your Google Cloud project. If you are using docker or another container registry instead, replace the entire image path.

   apiVersion: serving.knative.dev/v1alpha1
   kind: Service
   metadata:
     name: helloworld-python
     namespace: default
   spec:
     runLatest:
       configuration:
         revisionTemplate:
           spec:
             container:
               image: gcr.io/{PROJECT_ID}/helloworld-python
               env:
               - name: TARGET
                 value: "Python Sample v1"
   

Build and deploy this 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. For this example, we'll use Google Cloud Container Builder to build the sample into a container. To use container builder, execute the following gcloud command. Make sure to replace ${PROJECT_ID} with the ID of your Google Cloud project.

   gcloud container builds submit --tag gcr.io/${PROJECT_ID}/helloworld-python
   

2. After the build has completed, you can deploy the app into your cluster. Ensure that the container image value in service.yaml matches the container you build in the previous step. Apply the configuration using kubectl:

   kubectl apply -f service.yaml
   

3. Now that your service is created, Knative will perform the following steps:

   • Create a new immutable revision for this version of the app.
   • Network programming to create a route, ingress, service, and load balance for your app.
   • Automatically scale your pods up and down (including to zero active pods).

4. To find the URL and IP address for your service, use kubectl to list the ingress points in the cluster:

   kubectl get ing
   
   NAME                        HOSTS                                                                                   ADDRESS        PORTS     AGE
   helloworld-python-ingress   helloworld-python.default.demo-domain.com,*.helloworld-python.default.demo-domain.com   35.232.134.1   80        1m
   

5. Now you can make a request to your app to see the result. Replace {IP_ADDRESS} with the address you see returned in the previous step.

   curl -H "Host: helloworld-python.default.demo-domain.com" http://{IP_ADDRESS}
   Hello World: Python Sample v1!
   

Remove the sample app deployment

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

kubectl delete -f service.yaml