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Skill: Docker Containerization (Node.js)

Purpose

To package a Node.js application and its dependencies into a lightweight, portable container image that runs consistently across any environment.

When to Use

  • When preparing an application for production deployment.
  • When ensuring development environment consistency.
  • When isolating microservices in a cluster (Kubernetes/ECS).

Procedure

1. Multi-Stage Dockerfile (TypeScript/Build)

Use multi-stage builds to keep the final production image as small as possible.

# Stage 1: Build
FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

# Stage 2: Production
FROM node:20-alpine
WORKDIR /app
ENV NODE_ENV=production

# Install only production dependencies
COPY package*.json ./
RUN npm ci --only=production

# Copy built assets from builder stage
COPY --from=builder /app/dist ./dist

# Security: Run as non-root user
USER node

EXPOSE 3000
CMD ["node", "dist/index.js"]

2. .dockerignore Configuration

Prevent unnecessary files from bloating the build context.

node_modules
npm-debug.log
dist
.git
.env
Dockerfile
.dockerignore

3. Docker Compose for Development

Simplify local development with linked services.

# docker-compose.yml
services:
  app:
    build: 
      context: .
      dockerfile: Dockerfile.dev
    ports:
      - "3000:3000"
    volumes:
      - .:/app
      - /app/node_modules
    environment:
      - DATABASE_URL=postgres://user:pass@db:5432/db
    depends_on:
      - db

  db:
    image: postgres:15
    environment:
      - POSTGRES_PASSWORD=pass

4. Building and Running

Commands for the CLI.

# Build the image
docker build -t my-app:v1 .

# Run the container
docker run -p 3000:3000 --env-file .env my-app:v1

Constraints

  • Base Image: Always use alpine or slim tags for smaller, more secure images.
  • Layer Caching: Copy package.json and install dependencies before copying the rest of the source code to leverage Docker layer caching.
  • Security: Never include .env files or hardcoded secrets in the image. Use environment variables at runtime.

Expected Output

A production-ready Dockerfile that produces a minimal, secure image containing only the necessary runtime files.