Introduction to Docker

Containerize Everything

🐳 Learn the basics of Docker containerization

What is Docker?

Container platform
Packages applications with dependencies
"Build once, run anywhere"
Lightweight alternative to VMs
Industry standard for deployment

Containers vs Virtual Machines

Virtual Machines

Full OS for each VM
Heavy resource usage
Slower to start
Complete isolation

Containers

Share host OS kernel
Lightweight
Start in seconds
Process isolation

Core Concepts

Image

Read-only template with application

Container

Running instance of an image

Registry

Storage for Docker images

Dockerfile

Instructions to build an image

Basic Docker Commands

bash

# Pull an image
docker pull nginx

# List images
docker images

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

# List running containers
docker ps

Working with Containers

bash

# Stop container
docker stop <container-id>

# Start container
docker start <container-id>

# Remove container
docker rm <container-id>

# View logs
docker logs <container-id>

Creating a Dockerfile

dockerfile

# Base image
FROM node:18-alpine

# Set working directory
WORKDIR /app

# Copy package files
COPY package*.json ./

# Install dependencies
RUN npm install

# Copy app files
COPY . .

# Expose port
EXPOSE 3000

# Start command
CMD ["npm", "start"]

Building Images

bash

# Build image
docker build -t myapp:latest .

# Tag image
docker tag myapp:latest myapp:v1.0

# Push to registry
docker push myapp:v1.0

Build Best Practices

Use specific base image versions
Minimize layers
Order commands by change frequency
Use .dockerignore
Don't run as root

Docker Compose

Manage multi-container applications

yaml

version: '3.8'
services:
  web:
    build: .
    ports:
      - "3000:3000"
  
  db:
    image: postgres:15
    environment:
      POSTGRES_PASSWORD: secret

Compose Commands

bash

# Start services
docker-compose up -d

# Stop services
docker-compose down

# View logs
docker-compose logs

# Scale services
docker-compose up -d --scale web=3

Networking

Bridge Network

Default network for containers

Host Network

Share host's network

Custom Networks

bash

docker network create mynet
docker run --network mynet nginx

Volumes

Persist data beyond container lifecycle

bash

# Named volume
docker run -v mydata:/data nginx

# Bind mount
docker run -v /host/path:/container/path nginx

# List volumes
docker volume ls

Common Patterns

Multi-stage Builds

dockerfile

# Build stage
FROM node:18 AS builder
WORKDIR /app
COPY . .
RUN npm run build

# Production stage
FROM nginx:alpine
COPY --from=builder /app/dist /usr/share/nginx/html

Security Tips

✅ Use official images
✅ Scan for vulnerabilities
✅ Don't store secrets in images
✅ Run as non-root user
✅ Keep images updated

Debugging

bash

# Execute command in container
docker exec -it <container> bash

# Inspect container
docker inspect <container>

# View resource usage
docker stats

Start Containerizing!

Docker makes deployment consistent and scalable

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