Introduction

Containerization is a popular approach to package and deploy applications. Docker is a widely-used platform for creating, deploying, and running containers. In this guide, we'll explore how to containerize your Flask application using Docker, including creating a Dockerfile, building an image, and running containers.

Step 1: Install Docker

If you haven't already, you need to install Docker on your development machine. Visit the Docker website to download and install Docker for your specific operating system.

Step 2: Create a Dockerfile

A Dockerfile is a script that defines how to build a Docker image for your Flask application. Here's an example of a Dockerfile for a basic Flask app:

# Use an official Python runtime as a parent image
FROM python:3.8-slim
# Set the working directory to /app
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 --trusted-host pypi.python.org -r requirements.txt
# Make port 80 available to the world outside this container
EXPOSE 80
# Define environment variable
ENV NAME World
# Run app.py when the container launches
CMD ["python", "app.py"]
        

Step 3: Build the Docker Image

Use the `docker build` command to build a Docker image from your Dockerfile. Make sure you run this command in the same directory as your Dockerfile. Provide a tag for your image to make it easier to reference later.

docker build -t my-flask-app .
        

Step 4: Run a Docker Container

Use the `docker run` command to start a container from the image you built. Specify any necessary options, such as port mapping or environment variables. For example:

docker run -p 4000:80 my-flask-app
        

Step 5: Access Your Flask App

Your Flask app should now be running inside a Docker container. You can access it by opening a web browser and navigating to the IP address or hostname where the container is running. In this example, it would be http://localhost:4000.

Conclusion

Containerizing your Flask application with Docker provides a portable and consistent way to deploy your app across different environments. By following these steps, you can create a Docker image for your Flask app and run it as a container. Docker simplifies deployment and eliminates many of the "it works on my machine" issues that can arise in web development.