Build your first Docker Container

In this blog, let’s dive into building your first Docker image. We aim to create an Ubuntu-based image with Python 3 installed in it.

Why Build Your Docker Image?

Docker images are the foundation of containers. While public images on Docker Hub are convenient, building your image gives you control over the environment. This ensures consistency across your deployments and provides a deeper understanding of Docker's work.

Ready? Let’s get started!

Set Up Docker

First, make sure Docker is installed and running on your machine.

Follow this blog to install Docker on your Linux/WSL.

Verify installation by running:

docker --version

Create a Dockerfile

The Dockerfile is a simple text file with instructions to build your Docker image. Create a project directory to keep things tidy:

mkdir docker-python && cd docker-python

Now, create a file named Dockerfile:

PS: The file is Dockerfile with no extension

touch Dockerfile

Write the Dockerfile

Here’s what your Dockerfile should look like:

#Ubuntu as the base image  
FROM ubuntu:latest  

# Update and install Python 3  
RUN apt-get update && apt-get install -y python3

Let’s examine the above file

1. FROM ubuntu:latest: Starts with the latest Ubuntu base image.

2. RUN: Updates the package list and installs Python 3.

Build the Image

Time to turn the Dockerfile into a Docker image. Run:

docker build -t ubuntu-python3 .

Command Explanation:

• The -t ubuntu-python3 flag tags the image with a name. In our case it’s ubuntu-python3

• The . specifies the build context (current directory).

If everything goes well, Docker will download the Ubuntu base image and install Python 3.

Verify Your Image

Check if your image is built:

docker images

You should see ubuntu-python3 in the list.

Run a Container

Let’s test our image by running a container:

docker run ubuntu-python3

If everything goes well, your container should be running now.

Run the following command to confirm.

docker ps -a

Run the following command to connect to the docker container you just created

docker exec -it ubuntu-python3 /bin/bash

You should now see a “new terminal”. This is the terminal of your container.

Run python -V In the terminal, you will see the Python version.

If everything went well, you just built your first Docker image, ran it as a container and established a session with the container to run a command.