docker optimization security containers devops

Docker image optimization and security scanning

Ryan Nakamura Feb 2026

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# Optimized production Dockerfile

# Stage 1: Dependencies
FROM node:20-alpine AS deps
WORKDIR /app

# Install only production dependencies
COPY package.json package-lock.json ./
RUN npm ci --only=production &&     npm cache clean --force

# Stage 2: Build
FROM node:20-alpine AS builder
WORKDIR /app

COPY package.json package-lock.json ./
RUN npm ci

COPY tsconfig.json ./
COPY src/ ./src/

RUN npm run build &&     rm -rf src tsconfig.json

# Stage 3: Production
FROM node:20-alpine AS production

# Security: add non-root user
RUN addgroup -g 1001 -S nodejs &&     adduser -S appuser -u 1001 -G nodejs

# Security: remove unnecessary packages
RUN apk --no-cache add dumb-init &&     rm -rf /var/cache/apk/*

WORKDIR /app

# Copy production dependencies
COPY --from=deps --chown=appuser:nodejs /app/node_modules ./node_modules

# Copy built application
COPY --from=builder --chown=appuser:nodejs /app/dist ./dist
COPY --from=builder --chown=appuser:nodejs /app/package.json ./

# Security: read-only filesystem
RUN mkdir -p /app/tmp && chown appuser:nodejs /app/tmp

USER appuser

ENV NODE_ENV=production
EXPOSE 3000

HEALTHCHECK --interval=30s --timeout=3s --start-period=10s --retries=3   CMD node -e "require('http').get('http://localhost:3000/health', (r) => { process.exit(r.statusCode === 200 ? 0 : 1) })"

# Use dumb-init to handle signals properly
ENTRYPOINT ["dumb-init", "--"]
CMD ["node", "dist/server.js"]

#!/bin/bash
set -euo pipefail

IMAGE="myapp:latest"

# .dockerignore contents
cat > .dockerignore << 'EOF'
.git
.gitignore
node_modules
npm-debug.log
Dockerfile*
docker-compose*
.dockerignore
.env*
*.md
tests/
coverage/
.github/
.vscode/
EOF

# Build image
docker build -t "$IMAGE" .

# Check image size
echo "=== Image Size ==="
docker images "$IMAGE" --format "table {{.Repository}}	{{.Tag}}	{{.Size}}"

# Scan with Trivy
echo "=== Trivy Security Scan ==="
trivy image --severity HIGH,CRITICAL "$IMAGE"

# Scan with Docker Scout
echo "=== Docker Scout ==="
docker scout cves "$IMAGE"

# Check for secrets in image
echo "=== Secret Scanning ==="
trivy image --scanners secret "$IMAGE"

# List image layers
echo "=== Image Layers ==="
docker history "$IMAGE" --no-trunc

# Lint Dockerfile
echo "=== Hadolint ==="
hadolint Dockerfile

# Check running as non-root
echo "=== User Check ==="
docker run --rm "$IMAGE" whoami

echo "=== Scan Complete ==="

2 files · dockerfile, bash Explain with highlit

Optimized Docker images reduce build time, storage, and attack surface. Alpine-based images start at 5MB versus 100MB+ for Debian. Multi-stage builds separate build tools from runtime—final image contains only production artifacts. Layer ordering matters: copy dependency files first, then source code, maximizing cache hits. Use COPY --from=builder to extract built artifacts. RUN instructions should be combined with && to reduce layers. .dockerignore excludes node_modules, .git, and test files. Pin exact package versions for reproducibility. Run containers as non-root with USER directive. Use docker scout or trivy for vulnerability scanning. HEALTHCHECK enables container health monitoring. Image size directly impacts deployment speed and cold start time.