> ## Documentation Index > Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt > Use this file to discover all available pages before exploring further. # Demo Creating a new Docker Image > This guide explains how to build a custom Docker image for a Python Flask web application and push it to Docker Hub. Welcome to this detailed guide on building a custom Docker image for a simple Python Flask web application. In this tutorial, you'll learn how to set up the application, manually run it, containerize it using Docker, and finally push your image to Docker Hub. The complete project is available on my [GitHub page](https://github.com). *** ## Application Overview Our web application comprises a single file, `app.py`, which defines two routes: * The default route (`/`) displays a welcome message. * The `/how are you` route returns the response "I am good, how about you?". Below is the complete source code for `app.py`: ```python theme={null} import os from flask import Flask app = Flask(__name__) @app.route("/") def main(): return "Welcome!" @app.route('/how are you') def hello(): return 'I am good, how about you?' if __name__ == "__main__": app.run() ``` *** ## Deploying the Application Manually Before containerizing the application, you can deploy it manually on an Ubuntu host. Follow these steps: ### Installing Dependencies Update your package lists and install Python along with required packages: ```bash theme={null} apt-get update apt-get install -y python python-setuptools python-dev build-essential python-pip python-mysqldb ``` Next, install Flask and its MySQL helper using pip: ```bash theme={null} pip install flask pip install flask-mysql ``` To run the application manually, execute the command below: ```bash theme={null} FLASK_APP=app.py flask run --host=0.0.0.0 ``` Once running, access the following URLs in your web browser: * `http://:5000` – should display "Welcome!" * `http://:5000/how%20are%20you` – should display "I am good, how about you?" The console output will look similar to: ```plaintext theme={null} => Welcome => I am good, how about you? ``` *** ## Running the Application Inside a Docker Container Containerizing your application isolates the environment and simplifies dependency management. ### Starting an Ubuntu Container Launch an interactive Ubuntu container with a bash shell: ```bash theme={null} docker run -it ubuntu bash ``` Inside the container, update the package index and install Python: ```bash theme={null} apt-get update apt-get install -y python ``` If you encounter errors while installing Python due to an outdated package index, make sure to run `apt-get update` before attempting the installation. ### Installing pip and Flask If you receive a "pip: command not found" error, install pip: ```bash theme={null} apt-get install python-pip ``` Then install Flask using pip: ```bash theme={null} pip install flask ``` Successful installation will display messages confirming that Flask and its dependencies (itsdangerous, click, Werkzeug, Jinja2, MarkupSafe) have been installed. ### Running the Application After copying your application code into the container (for example, place it in `/opt/app.py`), run the application with: ```bash theme={null} FLASK_APP=app.py flask run --host=0.0.0.0 ``` The expected output is: ```plaintext theme={null} * Serving Flask app "app" * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit) ``` You can now access the application using the container's IP on port 5000. Visiting the `/how%20are%20you` route should trigger a GET request and display the correct response. *** ## Recording the Steps It's a good practice to record the commands executed for troubleshooting or later use. Below is an example command history: ```bash theme={null} apt-get update apt-get install -y python apt-get install python-pip pip install flask cat > /opt/app.py vi /opt/app.py FLASK_APP=app.py flask run --host=0.0.0.0 history ``` Keep these steps handy as you move forward to Dockerize your application. *** ## Dockerizing the Application After verifying your web application inside a Docker container, you can now create a Docker image. ### Creating a Dockerfile Create a project directory (e.g., `my-simple-webapp`) and add a file named `Dockerfile` with the following content: ```Dockerfile theme={null} FROM ubuntu # Update package lists and install Python and pip RUN apt-get update && apt-get install -y python python-pip # Install Flask via pip RUN pip install flask # Copy application source code into the container COPY app.py /opt/app.py # Set the entrypoint to run the Flask application ENTRYPOINT ["flask", "run", "--host=0.0.0.0", "--app", "/opt/app.py"] ``` Ensure that your `app.py` file is in the same directory as your `Dockerfile`. ### Building the Image Build your Docker image by running: ```bash theme={null} docker build . -t my-simple-webapp ``` Docker caches each layer, so subsequent builds without changes will be faster. To verify the image was built, list your Docker images: ```bash theme={null} docker images ``` Your image `my-simple-webapp` should appear in the list. ### Running the Docker Image To run your containerized application, execute: ```bash theme={null} docker run my-simple-webapp ``` Without port mapping, the application is accessible only from the host or via Docker’s internal IP. To make the application accessible externally, run: ```bash theme={null} docker run -p 5000:5000 my-simple-webapp ``` Then, navigate to `http://:5000` in your web browser. *** ## Pushing the Image to Docker Hub Sharing your application on Docker Hub is simple. Follow these steps: 1. Tag your image using your Docker Hub username (e.g., if your username is `mmumshad`): ```bash theme={null} docker build . -t mmumshad/my-simple-webapp ``` 2. Log in to Docker Hub: ```bash theme={null} docker login ``` Enter your username and password when prompted. 3. Push the image to Docker Hub: ```bash theme={null} docker push mmumshad/my-simple-webapp ``` If you encounter an error like “requested access to the resource is denied,” ensure that you have tagged your image with your Docker Hub account name and that you are logged in. Upon a successful push, your image will be available in your Docker Hub repository. You can view it on your Docker Hub dashboard. ![The image shows a Docker Hub webpage listing various public repositories with details on stars, pulls, and options to view more information.](https://kodekloud.com/kk-media/image/upload/v1752874143/notes-assets/images/Docker-Training-Course-for-the-Absolute-Beginner-Demo-Creating-a-new-Docker-Image/frame_1010.jpg) Others can pull your image by running: ```bash theme={null} docker pull mmumshad/my-simple-webapp ``` For private images, note that free Docker Hub accounts are limited to one private repository. ![The image shows a Docker Hub repository settings page, offering options to make the repository private or delete it, with warnings about irreversible actions.](https://kodekloud.com/kk-media/image/upload/v1752874145/notes-assets/images/Docker-Training-Course-for-the-Absolute-Beginner-Demo-Creating-a-new-Docker-Image/frame_1040.jpg) *** ## Summary In this guide, we covered: * Setting up a basic Flask web application. * Manually installing dependencies and running the application on an Ubuntu host. * Containerizing the application inside an Ubuntu Docker container. * Recording the installation and execution steps. * Creating a Dockerfile to build a custom image. * Building, running, and verifying the Docker image. * Tagging and pushing the image to Docker Hub for public distribution. Practice these steps to master Docker containerization and share your applications with the community. Happy containerizing!