Docker has become one of the most essential tools for developers. It allows you to package applications with all their dependencies into portable containers. In this blog post, you will build your first Docker image using the simplest possible example.
What Is a Docker Image?#
A Docker image is a read-only template that contains everything needed to run an application: - Source code - Runtime - Dependencies - System tools
When you run an image, Docker creates a container, which is a small isolated environment.
Step 1 - Create a Project Folder#
Start by creating a folder for your project:
mkdir myapp
cd myapp
Step 2 - Add a Simple Python Script#
Inside your myapp folder, create a file named app.py:
print("Hello from my Docker image!")
This small script will be what your container runs.
Step 3 - Create Your Dockerfile#
The Dockerfile tells Docker how to build your image. Create a file named Dockerfile:
# Use a small official Python image
FROM python:3.10-slim
# Copy script into image
COPY app.py /app.py
# Run script on container start
CMD ["python", "app.py"]
Step 4 - Build the Docker Image#
Run this from inside your project folder:
docker build -t my-first-image .
Docker will: 1. Download the base Python image 2. Add app.py into the image 3. Set the startup command
If everything works correctly, you will have your first image.
Step 5 - Run Your Docker Image#
Start a container by running:
docker run my-first-image
You should see:
Hello from my Docker image!
Congratulations. You have built and run your first Docker image.
What’s Next?#
Now that you understand the basic process, you can try: - Building images for web servers - Using docker-compose - Optimizing images with multi-stage builds - Publishing your image to Docker Hub
Docker is a powerful tool, and this is your starting point.