Docker

Docker

Docker standardizes software delivery by packaging apps into containers. In 2025, Docker emphasizes BuildKit for high-performance builds and Docker Scout for supply chain security.

When to Use

• Local Development: Replicate production environments locally (docker compose).
• CI/CD: Standard unit of deployment for 99% of modern pipelines.
• Legacy Migration: Wrap old apps in containers to extend their life.

Quick Start (BuildKit)

# syntax=docker/dockerfile:1
FROM node:22-alpine AS base
WORKDIR /app
COPY package*.json ./

FROM base AS deps
RUN npm ci

FROM base AS release
COPY --from=deps /app/node_modules ./node_modules
COPY . .
CMD ["node", "index.js"]

Core Concepts

BuildKit

The modern build engine (default in 2025). Features concurrent build steps, secret mounting, and cache exports. DOCKER_BUILDKIT=1 docker build .

Multi-stage Builds

Keep images tiny by separating "build" environment (compilers, SDKs) from "runtime" environment (minimal OS).

Docker Compose

Define multi-container apps. docker compose up -d --watch (New watch mode syncs files continuously).

Best Practices (2025)

Do:

• Use docker init: Generates best-practice Dockerfiles and .dockerignore for your language.
• Use Distroless / Alpine: Minimize attack surface.
• Scan with Docker Scout: Check for CVEs early in the pipeline.

Don't:

• Don't run as Root: Use USER node or create a specific user in the Dockerfile.
• Don't leak secrets: Use --mount=type=secret during build, never COPY .env.

References

• Docker Documentation

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