Diet Docker: How to Slash Your Image Size by 90%

I recently audited a client's infrastructure and found a simple Node.js microservice that was 1.2GB in size. Why? Because they blindly copied a FROM node:latest example and included their entire development toolchain in production. We got it down to 80MB.

The "node_modules" Black Hole

The biggest offender is dependencies. You need typescript, webpack, and jest to build your app, but you do NOT need them to run it. If you ship your devDependencies to production, you are shipping dead weight.

The Magic of Multi-Stage Builds

Docker allows you to use multiple FROM statements in a single Dockerfile. The first stage does the heavy lifting (compiling, building). The second stage copies only the artifacts from the first stage.

# Stage 1: Builder
FROM node:18 AS builder
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build

# Stage 2: Runner
FROM node:18-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/package*.json ./
RUN npm install --production
CMD ["node", "dist/index.js"]

This pattern discards the entire "Builder" environment. The final image only contains the compiled code and production dependencies.

Alpine Linux

Standard Linux images (like Ubuntu/Debian) include tools you don't need (curl, vim, git). Alpine Linux is a security-oriented, lightweight distro that is only ~5MB. Switching from node:18 to node:18-alpine can save 600MB instantly.

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