docker-containerization

Docker Containerization Skill

Step 1: Choose the Right Base Image

Use Case	Base Image
Python production	python:3.12-slim
Node.js production	node:20-alpine
Go production (final stage)	gcr.io/distroless/static
Debugging / dev	python:3.12 or node:20
Minimal static binary	scratch

Rules:

• Never use latest tag - pin exact versions for reproducibility
• Prefer -slim or -alpine over full images to reduce attack surface and size
• Use distroless or scratch for final stages of statically compiled languages

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Step 2: Production Dockerfiles

Python Application

# ─── Build Stage ─────────────────────────────────────────────────────────────
FROM python:3.12-slim AS builder

WORKDIR /app

# Install dependencies separately for layer caching
COPY requirements.txt .
RUN pip install --upgrade pip && \
    pip install --no-cache-dir --prefix=/install -r requirements.txt

# ─── Final Stage ─────────────────────────────────────────────────────────────
FROM python:3.12-slim

WORKDIR /app

# Copy installed packages from builder
COPY --from=builder /install /usr/local

# Create non-root user (security hardening)
RUN groupadd --gid 1001 appuser && \
    useradd --uid 1001 --gid appuser --shell /bin/bash --create-home appuser

# Copy application code
COPY --chown=appuser:appuser . .

USER appuser

EXPOSE 8000

# Health check
HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
    CMD curl -f http://localhost:8000/health || exit 1

CMD ["python", "-m", "uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]

Node.js Application

# ─── Dependencies Stage ───────────────────────────────────────────────────────
FROM node:20-alpine AS deps
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production

# ─── Build Stage (if TypeScript/Next.js) ─────────────────────────────────────
FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

# ─── Final Stage ─────────────────────────────────────────────────────────────
FROM node:20-alpine AS runner
WORKDIR /app

# Non-root user
RUN addgroup --gid 1001 nodejs && \
    adduser --system --uid 1001 nextjs

# Production dependencies only
COPY --from=deps --chown=nextjs:nodejs /app/node_modules ./node_modules
COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./
COPY --from=builder --chown=nextjs:nodejs /app/.next/static ./.next/static
COPY --from=builder --chown=nextjs:nodejs /app/public ./public

USER nextjs

EXPOSE 3000
ENV NODE_ENV=production PORT=3000

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