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Docker Guide

Complete guide to containerization with Docker, from basics to advanced patterns.

What is Docker?​

Docker is a platform for developing, shipping, and running applications in containers. Containers allow you to package an application with all its dependencies into a standardized unit for software development.

Getting Started​

Installation​

Install Docker on your system:

Ubuntu/Debian:

curl -fsSL https://get.docker.com -o get-docker.sh
sudo sh get-docker.sh

macOS/Windows: Download Docker Desktop from docker.com

Your First Container​

Run your first container:

docker run hello-world

Docker Basics​

Images​

Images are the blueprint for containers. Pull an image from Docker Hub:

docker pull nginx:latest

List all images:

docker images

Containers​

Create and run a container from an image:

docker run -d -p 80:80 --name my-nginx nginx:latest

List running containers:

docker ps

Stop a container:

docker stop my-nginx

Dockerfile​

Create custom images using a Dockerfile:

FROM node:18-alpine

WORKDIR /app

COPY package*.json ./

RUN npm install

COPY . .

EXPOSE 3000

CMD ["npm", "start"]

Build the image:

docker build -t my-app:latest .

Docker Compose​

Manage multi-container applications with Docker Compose:

version: '3.8'

services:
  web:
    build: .
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=production
    depends_on:
      - db

  db:
    image: postgres:15
    environment:
      - POSTGRES_PASSWORD=secretpassword
    volumes:
      - postgres-data:/var/lib/postgresql/data

volumes:
  postgres-data:

Run your application:

docker-compose up -d

Best Practices​

1. Use Specific Image Tags​

❌ Don't:

FROM node

✅ Do:

FROM node:18-alpine

2. Minimize Layers​

Combine RUN commands:

RUN apt-get update && \
    apt-get install -y package1 package2 && \
    apt-get clean && \
    rm -rf /var/lib/apt/lists/*

3. Use .dockerignore​

Create a .dockerignore file:

node_modules
npm-debug.log
.git
.gitignore
README.md
.env

4. Multi-stage Builds​

Reduce image size with multi-stage builds:

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

# Production stage
FROM node:18-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY package*.json ./
RUN npm install --production
CMD ["node", "dist/index.js"]

Common Commands Reference​

CommandDescription
docker psList running containers
docker ps -aList all containers
docker imagesList images
docker logs <container>View container logs
docker exec -it <container> bashEnter container shell
docker rm <container>Remove container
docker rmi <image>Remove image
docker system pruneClean up unused resources

Next Steps​