Lab05-01: Docker Basics

This guide provides a step-by-step walkthrough of fundamental Docker concepts and commands. It's designed as a practical lab manual to get you started with containerization.

Prerequisites

A machine running Ubuntu (20.04+ recommended)
Sudo or root privileges (required for installation and managing Docker daemon)
Internet access to download packages and images

Lab 1: Install Docker on Ubuntu

This section guides you through installing the Docker Engine on your Ubuntu system. We'll remove old versions, set up the official Docker repository, and install the latest stable version.

Remove any old Docker versions
- This step ensures a clean installation by removing potentially conflicting older packages of Docker or related components like containerd or runc.
```
sudo apt-get remove \\
  docker \\
  docker-engine \\
  docker.io \\
  containerd \\
  runc
```
Update package index and install prerequisites
- Updating the package index ensures you get the latest version information from repositories. The listed packages (apt-transport-https, ca-certificates, curl, software-properties-common) are necessary for adding and accessing external repositories over HTTPS.
```
sudo apt-get update
sudo apt-get install \\
  apt-transport-https \\
  ca-certificates \\
  curl \\
  software-properties-common
```
Add Docker’s official GPG key
- Adding the GPG key verifies the authenticity of the packages you download from the Docker repository, protecting against malicious package tampering.
```
curl -fsSL <https://download.docker.com/linux/ubuntu/gpg> \\
  | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg
```
Set up the stable repository
- This command adds the official Docker stable repository to your system's sources list. This tells apt where to find the Docker packages for your specific Ubuntu version (lsb_release -cs) and architecture (dpkg --print-architecture). The signed-by part links the repository to the GPG key we added.
```
echo \\
  "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] \\
  <https://download.docker.com/linux/ubuntu> \\
  $(lsb_release -cs) stable" \\
  | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
```
Install Docker Engine and CLI
- We update the package index again to include the newly added Docker repository. Then, we install the core components: docker-ce (the Community Edition engine), docker-ce-cli (the command-line interface), containerd.io (the container runtime), and necessary plugins for building and orchestration (docker-buildx-plugin, docker-compose-plugin).
```
sudo apt-get update
sudo apt-get install \\
  docker-ce \\
  docker-ce-cli \\
  containerd.io \\
  docker-buildx-plugin \\
  docker-compose-plugin
```
Verify installation
- This command simply checks if the docker command is available and reports its installed version, confirming the installation was successful.
```
docker --version
```
(Optional) Manage Docker as a non-root user
- By default, the Docker daemon binds to a Unix socket owned by root. Only root or users in the docker group can access it. Adding your user to the docker group allows you to run docker commands without sudo. Note: The docker group grants root-level privileges, so handle with care.
```
sudo usermod -aG docker $USER
# Then log out and back in, or run:
newgrp docker
```

Lab 2: Working with Images

Docker Images are read-only templates used to create containers. They contain the application code, libraries, dependencies,1 and configuration needed for an application to run. This lab explores how to build, inspect, share, and manage images.

2.1 Build an image from a Dockerfile
- A Dockerfile is a script that contains instructions for building a Docker image (e.g., specifying the base image, copying files, running commands). This command builds an image based on the Dockerfile in the current directory (.). The t myapp:latest option tags the image with a name (myapp) and a version (latest), making it easy to reference.
```
# From a directory with Dockerfile
docker image build -t myapp:latest .
```