Docker and Docker Compose Guide

Introduction

Docker is a platform for developing, shipping, and running applications inside containers. Docker Compose is a tool for defining and running multi-container Docker applications using YAML files. This guide covers essential Docker and Docker Compose commands, with practical examples, to help you manage containers effectively.

What is Docker?

Docker allows you to package applications with their dependencies into containers, ensuring consistency across different environments. Containers are lightweight, portable, and run independently of the host system.

What is Docker Compose?

Docker Compose simplifies the management of multi-container applications by defining services, networks, and volumes in a single YAML file. It allows you to start, stop, and configure multiple containers with a single command.

Prerequisites

  • Docker installed on your system (docker --version to verify).
  • Docker Compose installed (docker-compose --version or docker compose version for newer versions).
  • Basic understanding of terminal commands.

Basic Docker Commands

Container Management

# List running containers
docker ps

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

# Run a container
docker run -d --name my_container -p 8080:80 nginx

# Stop a container
docker stop my_container

# Start a stopped container
docker start my_container

# Remove a container
docker rm my_container

# Remove all stopped containers
docker container prune

Image Management

# List images
docker images

# Pull an image from Docker Hub
docker pull nginx:latest

# Build an image from a Dockerfile
docker build -t my_image:tag .

# Remove an image
docker rmi my_image:tag

# Remove unused images
docker image prune

Logs and Inspection

# View container logs
docker logs my_container

# Follow container logs in real-time
docker logs -f my_container

# Inspect container details
docker inspect my_container

# View container resource usage
docker stats

Docker Compose Basics

Docker Compose uses a docker-compose.yml file to define services. Below is an example for a web application with a database.

Example: Simple Web App with Nginx and MySQL

version: '3.8'
services:
  web:
    image: nginx:latest
    ports:
      - "8080:80"
    volumes:
      - ./html:/usr/share/nginx/html
    depends_on:
      - db
  db:
    image: mysql:8.0
    environment:
      MYSQL_ROOT_PASSWORD: example_password
      MYSQL_DATABASE: myapp
    volumes:
      - db_data:/var/lib/mysql
volumes:
  db_data:

Explanation

  • version: Specifies the Docker Compose file format.
  • services: Defines the containers (e.g., web for Nginx, db for MySQL).
  • ports: Maps host port 8080 to container port 80.
  • volumes: Persists MySQL data and mounts a local html folder for Nginx.
  • environment: Sets MySQL configuration variables.
  • depends_on: Ensures the database starts before the web service.

Docker Compose Commands

# Start services defined in docker-compose.yml
docker-compose up -d

# Stop and remove services
docker-compose down

# View logs for all services
docker-compose logs

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

# List running services
docker-compose ps

# Build or rebuild services
docker-compose build

# Restart services
docker-compose restart

# Remove stopped service containers
docker-compose rm -f

Useful Docker Commands

Networking

# List networks
docker network ls

# Create a custom network
docker network create my_network

# Run a container in a specific network
docker run -d --network my_network --name my_container nginx

# Inspect a network
docker network inspect my_network

Volumes

# List volumes
docker volume ls

# Create a volume
docker volume create my_volume

# Remove unused volumes
docker volume prune

# Inspect a volume
docker volume inspect my_volume

System Maintenance

# Remove all unused containers, networks, and images
docker system prune -a

# View Docker system information
docker info

# Check Docker version
docker --version

Practical Script

Create a script to monitor and manage a Docker Compose setup:

#!/bin/bash
# manage_docker.sh

echo "=== Docker Compose Management ==="
echo "Current directory: $(pwd)"
echo ""

echo "Starting services..."
docker-compose up -d

echo ""
echo "Running containers:"
docker-compose ps

echo ""
echo "System status:"
docker info --format '{{.ContainersRunning}} containers running, {{.Images}} images'

echo ""
echo "Cleaning up unused resources..."
docker system prune -f

Make it executable:

chmod +x manage_docker.sh
./manage_docker.sh

Pro Tips

Troubleshooting

  • Container Won’t Start: Check logs with docker logs <container_name> or docker-compose logs.
  • Port Conflicts: Ensure the host port (e.g., 8080) isn’t already in use (netstat -tuln).
  • Image Pull Issues: Verify internet connectivity or check Docker Hub for the image.
  • Volume Permission Issues: Ensure the host user has access to mounted directories.

Next Steps

In future tutorials, we’ll cover:

  • Writing efficient Dockerfiles.
  • Docker networking and service discovery.
  • Orchestration with Docker Swarm or Kubernetes.
  • CI/CD integration with Docker.

Practice Exercises

  1. Web App Setup: Create a docker-compose.yml for a Node.js app with a MongoDB database.
  2. Log Analysis: Write a script to tail logs from a specific service.
  3. Resource Cleanup: Create a script to remove all stopped containers and unused images.
  4. Multi-Container App: Build a Compose file for a web app, database, and cache (e.g., Redis).

Resources

Practice building and managing containers to master Docker and Docker Compose!