Docker ensures everyone runs the same environment — from junior developer to production server.
Core Concepts
Image: A template (like a class). Container: A running instance (like an object). Dockerfile: Recipe to build an image. docker-compose: Run multiple containers together.
Your First Dockerfile
FROM node:20-alpine → WORKDIR /app → COPY package*.json ./ → RUN npm ci → COPY . . → CMD ["node", "server.js"]
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