Building your own Flask web service
In this chapter, we will build our own web service using the Flask framework, dockerize it and register it in the registry.
Requirements
You will require docker in this example. You can find installation instructions here. For example, on Ubuntu you can install it with:
curl -fsSL https://get.docker.com -o get-docker.sh
sudo sh get-docker.sh
To create, build and register docker image you don’t need a compiled hscloud environment, howerver you will need it to deploy the image to kubernetes.
Steps
We create a simple Flask application:
# app.py
from flask import Flask
app = Flask(__name__)
@app.route('/')
def hello_world():
return 'Hello, World!'
if __name__ == '__main__':
app.run()
We can check if the application works by running it. First we start the virtual environment and install Flask:
# for Linux and macOS environments
python3 -m venv .venv
source .venv/bin/activate
# for Windows environments
py -m venv .venv
.venv\bin\Activate.bat
After that:
pip3 install flask
python3 app.py
Now we create Dockerfile file for our application:
# Use an official Python runtime as a base image
FROM python:3.12.0-bullseye
# Set the working directory in docker
WORKDIR /app
# Copy the current directory contents into the container at /app
COPY . /app
# Install any needed packages specified in requirements.txt
RUN pip install --upgrade pip && \
pip install flask gunicorn
# Set environment variables
ENV FLASK_APP=app.py
ENV FLASK_RUN_HOST=0.0.0.0
# Expose port 5000 for the Flask app to listen on
EXPOSE 5000
# Define command to run the application using gunicorn
CMD ["gunicorn", "-w", "4", "-b", ":5000", "app:app"]
We can test if the application works in Docker:
docker build -t myflask:2137 . # Build the image
docker run -p 5000:5000 myflask:2137 # Run the container
We can check if the application works by opening the browser at http://localhost:5000.
Pushing the image to the registry
First, we need to authenticate to the registry. That will require visiting the link in a web browser:
https://registry.k0.hswaw.net
You should get command similar to:
docker login -u $hs_username -p *************** https://registry.k0.hswaw.net
Run it in your environment.
Now we need to create local server for our docker image:
# create local server for our docker image. Replace $hs_username with your sso username
docker tag myflask:2137 registry.k0.hswaw.net/$hs_username/myflask:2137
docker push registry.k0.hswaw.net/$hs_username/myflask:2137
To remove the image from the registry, you can use:
# remove image from registry. Replace $hs_username with your sso username
docker rmi registry.k0.hswaw.net/$hs_username/myflask:2137