🐳 Docker & Containers

Containerizing applications for consistent environments and deployment.

Dockerfile best practices

# Use specific version, not :latest
FROM node:20-alpine

WORKDIR /app

# Copy dependency files first (cache layer)
COPY package.json package-lock.json ./
RUN npm ci --production

# Copy source code
COPY . .

# Non-root user
RUN addgroup -S app && adduser -S app -G app
USER app

EXPOSE 3000
CMD ["node", "server.js"]

Key principles

• One process per container — Don't run multiple services in one container
• Minimize image size — Use Alpine, multi-stage builds
• Layer caching — Put rarely-changing layers first
• No secrets in images — Use env vars or mounted secrets
• Immutable images — Same image across all environments

Multi-stage build

# Build stage
FROM node:20-alpine AS builder
WORKDIR /app
COPY . .
RUN npm ci && npm run build

# Production stage
FROM node:20-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
CMD ["node", "dist/server.js"]

Docker Compose (local dev)

services:
  app:
    build: .
    ports:
      - "3000:3000"
    environment:
      - DATABASE_URL=postgres://user:pass@db:5432/mydb
    depends_on:
      - db
  db:
    image: postgres:16-alpine
    volumes:
      - pgdata:/var/lib/postgresql/data
    environment:
      - POSTGRES_PASSWORD=pass

volumes:
  pgdata:

Common commands

Command	Purpose
docker build -t app .	Build image
docker run -p 3000:3000 app	Run container
docker compose up -d	Start all services
docker compose logs -f	Follow logs
docker exec -it <id> sh	Shell into container
docker system prune	Clean unused resources