docs/code-samples/serving/hello-world/helloworld-python

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:

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.
• Docker installed and running on your local machine, and a Docker Hub account configured.
• (optional) The Knative CLI client kn 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:

   mkdir app
   cd app
   

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

   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 for more details.

   # 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.

   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.

1. Use Docker to build the sample code into a container, then push the container to the Docker registry:

   # Build the container on your local machine
   docker build -t {username}/helloworld-python .
   
   # Push the container to docker registry
   docker push {username}/helloworld-python
   

Deploying the app

1. After the build has completed and the container is pushed to Docker Hub, you can deploy the app into your cluster.

=== "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"
    ```

   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"

   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.

   === "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:

   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
```