Docker Images: Why Is My Build 2GB?

Last Updated: November 2025
Scope: Docker, Node.js, Python

The Audit

docker images
# Look at the SIZE column

🚩 Red Flags:

• Node.js app >500MB
• Python app >1GB

The Fixes

Fix 1: Multi-Stage Builds

# ❌ Bad: Includes build tools in final image (800MB+)
FROM node:18
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build
CMD ["node", "dist/index.js"]

# ✅ Good: Build stage separate from runtime (150MB)
FROM node:18 AS builder
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build

FROM node:18-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
CMD ["node", "dist/index.js"]

Fix 2: Use Alpine Base Images

FROM node:18-alpine    # 40MB instead of 350MB
FROM python:3.11-slim  # 120MB instead of 900MB

Fix 3: Clean Up Package Managers

RUN npm ci --only=production && npm cache clean --force
# OR
RUN pip install --no-cache-dir -r requirements.txt

The Checklist

• Using multi-stage builds?
• Using alpine/slim base images?
• Cleaning package manager cache?