Docker Comprehensive Guide

This document provides a general overview and practical guide for using Docker in software development projects. It is suitable for beginners and intermediate users working with containerized applications.

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Table of Contents

• What is Docker?
• Key Concepts
• Basic Docker Commands
• Dockerfile Basics
• Docker Compose
• Volumes and Networks
• Best Practices
• Troubleshooting
• References

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What is Docker?

Docker is a platform for developing, shipping, and running applications inside lightweight containers. Containers package code and dependencies, ensuring consistency across environments.

Key Concepts

• Image: A snapshot of a filesystem and parameters for running a container.
• Container: A running instance of an image.
• Dockerfile: Script to build images.
• Volume: Persistent storage for containers.
• Network: Communication layer between containers.

Basic Docker Commands

# Build an image from a Dockerfile
docker build -t <image_name> .

# Run a container from an image
docker run -d -p <host_port>:<container_port> <image_name>

# List running containers
docker ps

# Stop a container
docker stop <container_id>

# Remove a container
docker rm <container_id>

# Remove an image
docker rmi <image_id>

Dockerfile Basics

A Dockerfile defines how to build a Docker image. Example:

FROM node:18
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
EXPOSE 3000
CMD ["npm", "start"]

Docker Compose

Docker Compose allows you to define and run multi-container applications using a compose.yml or docker-compose.yml file.

Example:

version: "3.8"
services:
    app:
        build: .
        ports:
            - "3000:3000"
    db:
        image: mongo
        ports:
            - "27017:27017"

Volumes and Networks

• Volumes: Persist data outside containers.

  docker volume create mydata
  docker run -v mydata:/data <image>

• Networks: Isolate and connect containers.

  docker network create mynet
  docker run --network=mynet <image>

Best Practices

• Use .dockerignore to exclude unnecessary files.
• Keep images small and use official base images.
• Tag images with meaningful names and versions.
• Use environment variables for configuration.
• Clean up unused images and containers regularly.

Troubleshooting

• Build errors: Check Dockerfile syntax and paths.
• Port conflicts: Ensure host ports are available.
• Permission issues: Use correct user permissions in containers.
• Networking issues: Verify network configuration and container connectivity.

References

• Docker Documentation
• Docker Compose Docs
• Awesome Docker

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For project-specific Docker instructions, see the Docker guides in each subfolder.