Docker image was 1.2GB — dropped to 180MB with multi-stage build

Pushing a Node.js Docker image to ECR was taking 4+ minutes every CI run. docker image ls showed the image was sitting at 1.2GB. Cold pulls in EKS were slow enough to cause pod startup timeouts.

Root cause: The Dockerfile was using node:18 as the base image and installing all dev dependencies (npm install without --omit=dev). The full Node.js image includes build tools, Python, and compilers that have no place in a production runtime.

Fix:

Before — single-stage Dockerfile (1.2GB):

FROM node:18
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build
CMD ["node", "dist/index.js"]

After — multi-stage build (180MB):

FROM node:18-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build
 
FROM node:18-alpine AS runtime
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
EXPOSE 3000
CMD ["node", "dist/index.js"]

Check the size difference:

docker build -t my-app:optimized .
docker image ls my-app

Lesson: Always use multi-stage builds for Node.js, Go, and Java apps — the builder stage carries tools you never need at runtime, and Alpine images alone cut 60–70% of image size.