Docker for Developers

Docker Basics

Docker is a platform for developing, shipping, and running applications inside containers. Containers package software with all dependencies for consistent execution.

Key Concepts

• Images: Blueprints for containers
• Containers: Running instances of images
• Dockerfile: Instructions to build images
• Registry: Repository for storing and sharing images

Creating a Dockerfile

FROM node:16-alpine
  WORKDIR /app
  COPY package*.json ./
  RUN npm install
  COPY . .
  EXPOSE 3000
  CMD ["npm", "start"]

Building and Running Containers

Build an image:

docker build -t my-app .

Run a container:

docker run -p 3000:3000 my-app

Docker Compose

Define multi-container applications with docker-compose.yml:

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

Development Workflow

Docker simplifies "works on my machine" issues by providing consistent environments. Use volumes to mount source code for live reloading:

docker run -v $(pwd):/app -p 3000:3000 my-app

Best Practices

• Use multi-stage builds to reduce image size
• Don't store secrets in images
• Use .dockerignore to exclude unnecessary files
• Tag images with versions for reproducibility

Docker is essential for modern development workflows, especially in team environments and CI/CD pipelines.