Hello World - Python

    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:

    • A Kubernetes cluster with Knative installed and DNS configured. Follow the installation instructions if you need to create one.
    • installed and running on your local machine, and a Docker Hub account configured (we’ll use it for a container registry).

    1. Create a new directory and cd into it:

      1. mkdir app
      2. cd app

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

      1. import os
      3. from flask import Flask
      5. app = Flask(__name__)
      7. @app.route('/')
      8. def hello_world():
      9.    return 'Hello {}!\n'.format(target)
      11. if __name__ == "__main__":

    4. Create a .dockerignore file to ensure that any files related to a local build do not affect the container that you build for deployment.

      1. Dockerfile
      2. README.md
      3. *.pyc
      4. *.pyo
      5. *.pyd
      6. __pycache__

    5. Create a new file, service.yaml and copy the following service definition into the file. Make sure to replace {username} with your Docker Hub username.

      1. apiVersion: serving.knative.dev/v1
      2. kind: Service
      3. metadata:
      4.   name: helloworld-python
      5.   namespace: default
      6.   template:
      7.     spec:
      8.       containers:
      9.         - image: docker.io/{username}/helloworld-python
      10.           env:
      11.             - name: TARGET
      12.               value: "Python Sample v1"

    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.

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

      1. kubectl apply --filename 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 for your service, use

      1. kubectl get ksvc helloworld-python  --output=custom-columns=NAME:.metadata.name,URL:.status.url
      2. NAME                URL
      3. helloworld-python   http://helloworld-python.default.1.2.3.4.xip.io

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

    1. kubectl delete --filename service.yaml