Docker Documentation

Introduction to Docker

Docker is a platform for developing, shipping, and running applications in containers. Containers are lightweight, portable, and self-contained units that can run anywhere Docker is installed.

Key Concepts

1. Containers

• Isolated environments that package application code and dependencies
• Share the host OS kernel but run in isolation
• Lightweight and fast to start/stop

2. Images

• Read-only templates used to create containers
• Built from Dockerfiles
• Stored in registries (like Docker Hub)

3. Dockerfile

• Text file containing instructions to build an image
• Each instruction creates a layer in the image
• Example:

FROM node:14
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
EXPOSE 3000
CMD ["npm", "start"]

Basic Docker Commands

Container Management

# List running containers
docker ps

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

# Start a container
docker start <container_id>

# Stop a container
docker stop <container_id>

# Remove a container
docker rm <container_id>

Image Management

# List images
docker images

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

# Pull an image
docker pull <image_name>

# Remove an image
docker rmi <image_name>

Running Containers

# Run a container
docker run <image_name>

# Run with port mapping
docker run -p 8080:80 <image_name>

# Run in detached mode
docker run -d <image_name>

# Run with environment variables
docker run -e VAR_NAME=value <image_name>

Docker Compose

Docker Compose is a tool for defining and running multi-container applications.

Basic Usage

version: '3'
services:
  web:
    build: .
    ports:
      - "3000:3000"
  db:
    image: postgres
    environment:
      POSTGRES_PASSWORD: password

Common Commands

# Start services
docker-compose up

# Start in detached mode
docker-compose up -d

# Stop services
docker-compose down

# View logs
docker-compose logs

Best Practices

1. Use Official Images

   • Prefer official images from Docker Hub
   • Specify exact versions for stability

2. Optimize Image Size

   • Use multi-stage builds
   • Remove unnecessary files
   • Combine RUN commands

3. Security

   • Don't run containers as root
   • Scan images for vulnerabilities
   • Use secrets for sensitive data

4. Networking

   • Use Docker networks for container communication
   • Expose only necessary ports
   • Use host networking sparingly

Advanced Topics

Docker Networking

• Bridge network (default)
• Host network
• Overlay network
• Custom networks

Docker Volumes

• Named volumes
• Bind mounts
• tmpfs mounts

Docker Swarm

• Service creation
• Stack deployment
• Scaling services
• Rolling updates

Troubleshooting

Common Issues

1. Container won't start
2. Network connectivity problems
3. Volume mounting issues
4. Permission problems

Debugging Commands

# View container logs
docker logs <container_id>

# Inspect container
docker inspect <container_id>

# Execute command in running container
docker exec -it <container_id> /bin/bash

Resources

• Docker Official Documentation
• Docker Hub
• Docker GitHub Repository