🐳 Docker Deployment Mastery

⚠️ The Problems

• Dependency Hell: Conflicting library versions across applications
• Environment Drift: Dev, staging, and prod slowly diverge over time
• Slow Onboarding: New developers spend days setting up environments
• Scaling Pain: Each new server needs hours of manual configuration

📄 Example: Node.js App Dockerfile

# Layer 1: Start with Node.js 18 on Alpine Linux
FROM node:18-alpine

# Layer 2: Set working directory
WORKDIR /app

# Layer 3: Copy dependency manifests FIRST
COPY package*.json ./

# Layer 4: Install dependencies
RUN npm ci --only=production

# Layer 5: Copy application code LAST
COPY . .

# Metadata: which port to expose
EXPOSE 3000

# Define startup command
CMD ["node", "server.js"]

Scenario: Your web app needs to talk to a database.

# Create a custom network
docker network create myapp-network

# Run database on the network
docker run -d --name db \
  --network myapp-network \
  postgres:14

# Run app on the same network
docker run -d --name web \
  --network myapp-network \
  -p 3000:3000 \
  myapp:1.0

Now web connects to db using hostname "db"—Docker handles DNS automatically!

Containers are ephemeral—when stopped, changes are lost. Volumes solve this:

# Create a named volume
docker volume create db-data

# Mount it to the container
docker run -d --name db \
  --network myapp-network \
  -v db-data:/var/lib/postgresql/data \
  postgres:14

Database data now survives restarts, updates, and even container deletion!

🎬 Interactive Command Builder

Check options to build your run command:

📄 docker-compose.yml Example

version: '3.8'

services:
  web:
    build: .
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=production
      - DB_HOST=db
    depends_on:
      - db
    networks:
      - app-network
    volumes:
      - ./logs:/app/logs

  db:
    image: postgres:14
    environment:
      - POSTGRES_PASSWORD=secret
    volumes:
      - db-data:/var/lib/postgresql/data
    networks:
      - app-network

volumes:
  db-data:

networks:
  app-network:

🎯 Perfect For

📄 Example: devcontainer.json

{
  "name": "Node.js Dev Container",
  "image": "mcr.microsoft.com/devcontainers/javascript-node:18",
  
  "customizations": {
    "vscode": {
      "extensions": [
        "dbaeumer.vscode-eslint",
        "esbenp.prettier-vscode",
        "ms-azuretools.vscode-docker"
      ],
      "settings": {
        "terminal.integrated.defaultProfile.linux": "bash"
      }
    }
  },
  
  "forwardPorts": [3000],
  "postCreateCommand": "npm install",
  "remoteUser": "node"
}

What You Should Know Now

• Environment parity: Docker packages app + dependencies so behavior is consistent across laptops, staging, and production.
• Layered images: Efficient Dockerfiles place stable layers early and frequently changing code later to maximize cache reuse.
• Networks & service discovery: Containers on the same Docker network can communicate by service/container name.
• Persistent storage: Volumes keep important data safe beyond container lifecycle events.
• Build once, run anywhere: The same image can run in multiple environments with predictable results.
• Dev Containers: Team members can share identical development environments for faster onboarding and fewer setup issues.

Assessment Rules

• Total questions: 7
• One attempt per question during a run
• Passing score: 80% or higher
• Use Next to begin Assessment Q1