# Hello World - Python This guide describes the steps required to create the `helloworld-python` sample app and deploy it to your cluster. The sample app reads a `TARGET` environment variable, and prints `Hello ${TARGET}!`. If `TARGET` is not specified, `World` is used as the default value. You can also download a working copy of the sample, by running the following commands: ```bash git clone https://github.com/knative/docs.git knative-docs cd knative-docs/code-samples/serving/hello-world/helloworld-python ``` ## Prerequisites - A Kubernetes cluster with Knative installed and DNS configured. See [Install Knative Serving](https://knative.dev/docs/install/serving/install-serving-with-yaml). - [Docker](https://www.docker.com) installed and running on your local machine, and a Docker Hub account configured. - (optional) The Knative CLI client [kn](https://github.com/knative/client/releases) can be used to simplify the deployment. Alternatively, you can use `kubectl`, and apply resource files directly. ## Build 1. Create a new directory and cd into it: ```bash mkdir app cd app ``` 2. Create a file named `app.py` and copy the following code block into it: ```python import os from flask import Flask app = Flask(__name__) @app.route('/') def hello_world(): target = os.environ.get('TARGET', 'World') return 'Hello {}!\n'.format(target) if __name__ == "__main__": app.run(debug=True,host='0.0.0.0',port=int(os.environ.get('PORT', 8080))) ``` 3. In your project directory, create a file named `Dockerfile` and copy the following code block into it. See [official Python docker image](https://hub.docker.com/_/python/) for more details. ```dockerfile # Use the official lightweight Python image. # https://hub.docker.com/_/python FROM python:3.7-slim # Allow statements and log messages to immediately appear in the Knative logs ENV PYTHONUNBUFFERED True # Copy local code to the container image. ENV APP_HOME /app WORKDIR $APP_HOME COPY . ./ # Install production dependencies. RUN pip install Flask gunicorn # Run the web service on container startup. Here we use the gunicorn # webserver, with one worker process and 8 threads. # For environments with multiple CPU cores, increase the number of workers # to be equal to the cores available. CMD exec gunicorn --bind :$PORT --workers 1 --threads 8 --timeout 0 app:app ``` 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. ```ignore Dockerfile README.md *.pyc *.pyo *.pyd __pycache__ ``` **NOTE:** Use Docker to build the sample code into a container. To build and push to Docker Hub or container registry of your choice, run these commands replacing `{username}` with your Docker Hub username or the URL of the container registry. 5. Use Docker to build the sample code into a container, then push the container to the Docker registry: ```bash # Build and push the container on your local machine. docker buildx build --platform linux/arm64,linux/amd64 -t "{username}/helloworld-python" --push . ``` ## Deploying the app After the build has completed and the container is pushed to Docker Hub, you can deploy the app into your cluster. Choose one of the following methods to deploy the app: ### yaml 1. 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 or with the URL provided by your container registry ```yaml apiVersion: serving.knative.dev/v1 kind: Service metadata: name: helloworld-python namespace: default spec: template: spec: containers: - image: docker.io/{username}/helloworld-python env: - name: TARGET value: "Python Sample v1" ``` 1. Ensure that the container image value in `service.yaml` matches the container you built in the previous step. Apply the configuration using `kubectl`: ```bash kubectl apply --filename service.yaml ``` ### kn 1. With `kn` you can deploy the service with ```bash kn service create helloworld-python --image=docker.io/{username}/helloworld-python --env TARGET="Python Sample v1" ``` This will wait until your service is deployed and ready, and ultimately it will print the URL through which you can access the service. During the creation of your service, Knative performs the following steps: - Creates 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 scales your pods up and down, including scaling down to zero active pods. ## Verification 1. Run one of the followings commands to find the domain URL for your service. > Note: If your URL includes `example.com` then consult the setup instructions for > configuring DNS (e.g. with `sslip.io`), or [using a Custom Domain](https://knative.dev/docs/serving/using-a-custom-domain). ### kubectl ```bash kubectl get ksvc helloworld-python --output=custom-columns=NAME:.metadata.name,URL:.status.url ``` Example: ```bash NAME URL helloworld-python http://helloworld-python.default.1.2.3.4.sslip.io ``` ### kn ```bash kn service describe helloworld-python -o url ``` Example: ```bash http://helloworld-python.default.1.2.3.4.sslip.io ``` 1. Now you can make a request to your app and see the result. Replace the following URL with the URL returned in the previous command. Example: ```bash curl http://helloworld-python.default.1.2.3.4.sslip.io Hello Python Sample v1! # Even easier with kn: curl $(kn service describe helloworld-python -o url) ``` > Note: Add `-v` option to get more detail if the `curl` command failed. ## Removing To remove the sample app from your cluster, delete the service record: ### kubectl ```bash kubectl delete --filename service.yaml ``` ### kn ```bash kn service delete helloworld-python ```