Docker: From Basics to Advanced

Docker is an open-source platform designed to simplify application deployment. It ensures that applications run reliably regardless of the environment.
It allows developers to build, ship, and run applications in isolated environments called containers. Containers package applications with their libraries, dependencies, and configurations, ensuring consistency across development, testing, and production.

• Consistency: Applications behave the same in development, testing, and production.
• Lightweight: Containers share the host OS kernel, making them more efficient than virtual machines.
• Portable: Run applications anywhere, from local machines to cloud platforms.

1. Install Docker on Linux

# Update the package index
sudo apt update

# Install required packages
sudo apt install apt-transport-https ca-certificates curl software-properties-common -y

# Add Docker's official GPG key
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

# Add the Docker repository
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
sudo apt update
sudo apt install docker-ce docker-ce-cli containerd.io -y

# Verify the installation
docker --version

2. Install Docker on macOS

• Requires macOS 10.14 or newer
• Ensure adequate resources are available for Docker Desktop

# Download Docker Desktop for Mac from:
https://www.docker.com/products/docker-desktop/

# Install Docker by dragging it to the Applications folder
# Open Docker Desktop and follow setup instructions

3. Install Docker on Windows

Docker Desktop supports Windows 10 64-bit (Professional, Enterprise, Education) and Windows 11

Steps:

1. Download Docker Desktop from Docker's official website.
2. Run the installer and follow on-screen instructions.
3. After installation, verify with:

docker --version

Useful Tips

Add your user to the Docker group to run Docker without sudo:

sudo usermod -aG docker $USER

Log out and log back in for changes to take effect.

Containers share host resources. Ensure sufficient CPU and memory allocation for performance.

• Docker Desktop: Includes GUI tools, ideal for macOS and Windows.
• Docker Engine: Lightweight CLI-based version for Linux servers.

Verify Your Docker Installation

Run a test container:

docker run hello-world

Expected output:

Hello from Docker!
This message shows that your installation appears to be working correctly.

Docker Command Reference

Basic Commands

• Check Docker Version

docker --version

• List Docker Images

docker images

• List Running Containers

docker ps

• List All Containers

docker ps -a

• Run a Container

docker run [OPTIONS] IMAGE [COMMAND] [ARG...]

• Stop a Running Container

docker stop CONTAINER_ID

• Remove a Container

docker rm CONTAINER_ID

• Remove an Image

docker rmi IMAGE_ID

Building Docker Images

• Build an Image from a Dockerfile

docker build -t IMAGE_NAME:TAG PATH

• Build Without Cache

docker build --no-cache -t IMAGE_NAME:TAG PATH

• View Build History

docker history IMAGE_NAME:TAG

Dockerfile Basics

Example:

# Use a base image
FROM ubuntu:latest

# Set environment variables
ENV MY_ENV_VAR=value

# Install dependencies
RUN apt-get update && apt-get install -y curl

# Copy files
COPY ./local_file /container_file

# Define default command
CMD ["echo", "Hello, Docker!"]

Networking and Volumes

• Create a Network

docker network create my_network

• Run a Container on a Network

docker run --network my_network IMAGE_NAME

• Create a Volume

docker volume create my_volume

• Run with a Volume

docker run -v my_volume:/container_path IMAGE_NAME

Docker Compose

• Start Services

docker-compose up

• Detached Mode

docker-compose up -d

• Stop Services

docker-compose down

• View Logs

docker-compose logs

Registry Operations

• Push to Docker Hub

docker push IMAGE_NAME:TAG

• Pull from Docker Hub

docker pull IMAGE_NAME:TAG

• Tag an Image

docker tag SOURCE_IMAGE:TAG TARGET_IMAGE:TAG

• Login

docker login

Troubleshooting and Scenarios

Scenario 1: Container Not Starting

• Symptom: Container exits immediately
• Solution: Check logs

docker logs CONTAINER_ID

Ensure command is valid and not terminating.

Use -it to keep the container interactive during debugging.

Scenario 2: Image Build Fails

• Symptom: docker build fails

• Solution:

• Review error messages

• Ensure Dockerfile syntax is correct

• Use no-cache build:

  docker build --no-cache -t IMAGE_NAME:TAG .
  

Cached layers may cause outdated dependencies. Use --no-cache to ensure fresh builds.

Scenario 3: Port Already in Use

• Symptom: Port conflict error

• Solution:

• Identify process:

  lsof -i :PORT
  

• Stop conflicting process or map a new port:

  docker run -p NEW_PORT:CONTAINER_PORT IMAGE_NAME
  

Use docker ps to review port mappings of running containers.

Scenario 4: Cannot Remove Container/Image

• Symptom: Removal fails with "in use" error

• Solution:

• Stop all containers:

  docker stop $(docker ps -q)
  

• Force remove:

  docker rm -f CONTAINER_ID
  docker rmi -f IMAGE_ID
  

The -f flag forces removal even when containers or images are in use.