Getting Started with Docker

Docker is a tool (primarily a linux-based) that lets you package your application and everything it needs to run into a single container, so it works the same on any computer.

1. What is a docker

Consider a scenario:

There is a linux machine with following configuration.

Ubuntu Linux 22.04
Python 3.10
OpenCV version 4.4

Now you wnat to run an application about robotic vision which required different set of tools as follows:

Ubuntu Linux 22.04
Python 3.12
OpenCV version 4.2 (4.4 is not compatible with our robotic application)

Current vs Required Tools

2. We create an ISOLATED container

The ubunutu machine is not only running many other applications besides this new application robotic vision. By changing the python verion and OpenCV version may break other applications.

So what to do in this case? We create an ISOLATED space in which we run new application alongwith all necessary tools and configuration settings.

This new isolated space is called a container (or docker).

Docker Inside a Physical Machine

3. Multiple docker containers

This idea can be extended to include many dockers containers in a single machine, as shown below. In each case, we can chose different tools, version and configurations.

Multiple Dockers

4. Docker installation

Docker is an application that enables the creation of isolated environments called containers. If Docker is not installed on your system, follow these steps to install it:

You can check if docker is installed or not:

docker --version

if you see an out like docker command not found, then following the steps below.

Step 1: Install dependencies

sudo apt update
sudo apt install \
    ca-certificates \
    curl \
    gnupg \
    lsb-release -y

Step 2: Add docker’s official GPG key

sudo mkdir -p /etc/apt/keyrings
curl -fsSL https://download.docker.com/linux/debian/gpg | \
    sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg

Step 3: Add docker's repository

Find debian codename by lsb_release -c (code name can be "bookwork" or "buster", or "bullseye" etc.)
$(lsb_release -cs) is replaced with your Debian codename (e.g., bullseye, bookworm):

General CommandDebian (Bookworm) Command

echo \
  "deb [arch=$(dpkg --print-architecture) \
  signed-by=/etc/apt/keyrings/docker.gpg] \
  https://download.docker.com/linux/debian \
  $(lsb_release -cs) stable" | \
  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

echo \
  "deb [arch=$(dpkg --print-architecture) \
  signed-by=/etc/apt/keyrings/docker.gpg] \
  https://download.docker.com/linux/debian \
  bookworm stable" | \
  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

Step 4: Install docker

sudo apt update
sudo apt install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin -y

Step 5: Verify installation

docker --version

You should see an output like:

Docker version 28.3.3, build 980b856

5. Summary

Docker is a tool that allows multiple applications to run in isolation from each other on the same machine.
Each application is packaged along with its code and the tools needed to run it, ensuring consistency.
If one Docker container fails, it does not affect other running containers.
Applications can be easily moved across machines since everything needed to run them is bundled together, eliminating the need for separate installations and configurations.

Containers

CI/CD