We use analytics and cookies to understand site traffic. Information about your use of our site is shared with Google for that purpose. Learn more.
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 -b "master" https://github.com/knative/docs knative-docs
cd knative-docs/docs/serving/samples/hello-world/helloworld-python
Prerequisites
- A Kubernetes cluster with Knative installed and DNS configured. Follow the installation instructions.
- 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
-
Create a new directory and cd into it:
mkdir app cd app
-
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', '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)))
-
In your project directory, create a file named
Dockerfile
and copy the code block below 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
-
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.
-
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
-
After the build has completed and the container is pushed to Docker Hub, you can deploy the app into your cluster.
-
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 registryapiVersion: 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 usingkubectl
:kubectl apply --filename service.yaml
With
kn
you can deploy the service withkn 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
-
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. withxip.io
), or using a Custom Domain.kubectl get ksvc helloworld-python --output=custom-columns=NAME:.metadata.name,URL:.status.url
Example:
NAME URL helloworld-python http://helloworld-python.default.1.2.3.4.xip.io
kn service describe helloworld-python -o url
Example:
http://helloworld-python.default.1.2.3.4.xip.io
-
Now you can make a request to your app and see the result. Replace the URL below with the URL returned in the previous command.
Example:
curl http://helloworld-python.default.1.2.3.4.xip.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 thecurl
command failed.
Removing
To remove the sample app from your cluster, delete the service record.
kubectl delete --filename service.yaml
kn service delete helloworld-python
Feedback
Was this page helpful?
Glad to hear it! Please tell us how we can improve.
Sorry to hear that. Please tell us how we can improve.