Docker Beginner's Guide: Installation and Essential Commands

Docker is an open-source platform that lets you run applications in isolated containers. It provides a consistent environment from development to production. This guide covers Docker installation, essential commands, and practical usage scenarios.

What is Docker?

Docker packages applications and their dependencies into portable containers. Unlike virtual machines:

Shares the host OS kernel (much lighter)
Starts and stops in seconds
Uses far fewer resources
Eliminates the "works on my machine" problem

Docker is the cornerstone of modern software development and deployment. On REXE servers, you can easily deploy applications using Docker.

Installing Docker

Debian/Ubuntu

hljs bash

# Remove old versions
sudo apt remove docker docker-engine docker.io containerd runc

# Install prerequisites
sudo apt update
sudo apt install ca-certificates curl gnupg lsb-release -y

# Add Docker GPG key
sudo mkdir -p /etc/apt/keyrings
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg

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

# Install Docker
sudo apt update
sudo apt install docker-ce docker-ce-cli containerd.io docker-compose-plugin -y

# Start and enable service
sudo systemctl start docker
sudo systemctl enable docker

RHEL/CentOS/AlmaLinux

hljs bash

# Add Docker repository
sudo dnf config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo

# Install Docker
sudo dnf install docker-ce docker-ce-cli containerd.io docker-compose-plugin -y

# Start service
sudo systemctl start docker
sudo systemctl enable docker

Verify Installation

hljs bash

# Check Docker version
docker --version

# Run test container
sudo docker run hello-world

# Use Docker without sudo
sudo usermod -aG docker $USER
newgrp docker

Essential Docker Commands

Running Containers

hljs bash

# Run a simple container
docker run nginx

# Run in background (detached)
docker run -d nginx

# Run with port mapping
docker run -d -p 8080:80 nginx

# Run with a name
docker run -d --name web-server -p 8080:80 nginx

# Run with environment variable
docker run -d -e MYSQL_ROOT_PASSWORD=secret --name mysql mysql:8.0

# Run with volume mount
docker run -d -v /host/dir:/container/dir nginx

# Auto-restart policy
docker run -d --restart unless-stopped nginx

# Interactive terminal
docker run -it ubuntu bash

Container Management

hljs bash

# List running containers
docker ps

# List all containers (including stopped)
docker ps -a

# Stop a container
docker stop container_name

# Start a container
docker start container_name

# Restart a container
docker restart container_name

# Remove a container (must be stopped first)
docker rm container_name

# Force remove running container
docker rm -f container_name

# Remove all stopped containers
docker container prune

Container Monitoring

hljs bash

# View container logs
docker logs container_name

# Follow logs in real-time
docker logs -f container_name

# Last 100 lines of logs
docker logs --tail 100 container_name

# Container resource usage
docker stats

# Container details
docker inspect container_name

# Attach to container shell
docker exec -it container_name bash

# Run command in container
docker exec container_name ls /var/www

Image Management

hljs bash

# Pull an image
docker pull nginx
docker pull nginx:1.25
docker pull ubuntu:22.04

# List local images
docker images

# Remove an image
docker rmi nginx

# Remove unused images
docker image prune

# Remove all unused resources
docker system prune -a

# Show image sizes
docker images --format "table {{.Repository}}\t{{.Tag}}\t{{.Size}}"

Building Images with Dockerfile

hljs dockerfile

# Example Dockerfile
FROM node:18-alpine

WORKDIR /app

COPY package*.json ./
RUN npm install --production

COPY . .

EXPOSE 3000

CMD ["node", "server.js"]

hljs bash

# Build image
docker build -t myapp:1.0 .

# Push to Docker Hub
docker tag myapp:1.0 username/myapp:1.0
docker push username/myapp:1.0

Volume Management

Volumes ensure data persists even when containers are removed.

hljs bash

# Create a volume
docker volume create database-data

# List volumes
docker volume ls

# Mount volume to container
docker run -d -v database-data:/var/lib/mysql mysql:8.0

# Bind mount (host directory)
docker run -d -v /root/data:/app/data nginx

# Remove a volume
docker volume rm database-data

# Remove unused volumes
docker volume prune

# Volume details
docker volume inspect database-data

Networking Basics

hljs bash

# List networks
docker network ls

# Create custom network
docker network create app-network

# Connect containers to network
docker run -d --network app-network --name web nginx
docker run -d --network app-network --name db mysql:8.0

# Containers on same network can reach each other by name
# From web container: ping db

# Network details
docker network inspect app-network

# Remove network
docker network rm app-network

Practical Examples

Nginx Web Server

hljs bash

docker run -d \
  --name nginx-web \
  -p 80:80 \
  -v /var/www/html:/usr/share/nginx/html:ro \
  --restart unless-stopped \
  nginx:alpine

MySQL Database

hljs bash

docker run -d \
  --name mysql-db \
  -e MYSQL_ROOT_PASSWORD=strong_password \
  -e MYSQL_DATABASE=myapp \
  -v mysql-data:/var/lib/mysql \
  -p 3306:3306 \
  --restart unless-stopped \
  mysql:8.0

WordPress + MySQL

hljs bash

# Create network
docker network create wordpress-net

# Start MySQL
docker run -d \
  --name wordpress-db \
  --network wordpress-net \
  -e MYSQL_ROOT_PASSWORD=root_pass \
  -e MYSQL_DATABASE=wordpress \
  -e MYSQL_USER=wp_user \
  -e MYSQL_PASSWORD=wp_pass \
  -v wp-db-data:/var/lib/mysql \
  mysql:8.0

# Start WordPress
docker run -d \
  --name wordpress \
  --network wordpress-net \
  -e WORDPRESS_DB_HOST=wordpress-db \
  -e WORDPRESS_DB_USER=wp_user \
  -e WORDPRESS_DB_PASSWORD=wp_pass \
  -e WORDPRESS_DB_NAME=wordpress \
  -p 8080:80 \
  wordpress:latest

For managing multiple containers, use Docker Compose. A docker-compose.yml file lets you start all services with a single command.

Conclusion

Docker is an indispensable tool for modern application deployment. Once you master the basics, move on to Docker Compose for multi-service management. On REXE servers, Docker lets you run applications in an isolated, secure, and portable manner.

Docker Beginner's Guide: Installation and Essential Commands

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