Docker simplifies how we build, ship, and run applications by following a clear lifecycle.
Let’s break it down into three main stages with an easy-to-follow example using Ubuntu and a small Python app.

1️⃣ Create the Dockerfile

A Dockerfile is like a recipe for your application. It tells Docker:

• Which base image to start from
• What dependencies to install
• What command to run when the container starts

Example:

# Start with an official Ubuntu image
FROM ubuntu:22.04

# Install Python
RUN apt-get update && apt-get install -y python3

# Copy our app to the container
COPY app.py /app/app.py

# Set working directory
WORKDIR /app

# Run the app when container starts
CMD ["python3", "app.py"]

2️⃣ Build the Docker Image

The Dockerfile is just instructions. To actually create something runnable, we build an image:

Using the Dockerfile, a Docker image is created through the docker build command. A Docker image is a lightweight, standalone, and executable package that includes everything needed to run an application, such as the runtime environment, system tools, libraries, and dependencies.

docker build -t ubuntu-simple-app .

What happens here?

• Docker takes the Ubuntu image
• Installs Python
• Copies app.py into it
• Creates a ready-to-use image named ubuntu-simple-app

3️⃣ Run the Docker Container

Once the image is built, a Docker container is created and executed using the docker run command. A container is an isolated environment where the application runs consistently across different systems. Containers leverage the lightweight nature of Docker images, ensuring minimal overhead and fast deployment.

docker run --name my-simple-app ubuntu-simple-app

Example app (app.py):

print("Hello from inside my Ubuntu-based Docker container!")

Output:

Hello from inside my Ubuntu-based Docker container!

🔄 Quick Recap

1. Dockerfile → Your recipe for building the image
2. Build Image → Turn recipe into a runnable package
3. Run Container → Launch the app in an isolated environment

By following this lifecycle, you ensure your app runs consistently anywhere — your laptop, a server, or the cloud.

💡 Pro Tip:

You can share your image with others via Docker Hub:

docker tag ubuntu-simple-app your-dockerhub-username/ubuntu-simple-app
docker push your-dockerhub-username/ubuntu-simple-app