Lesson 14

Multi-stage builds

This page shows how Docker can use one stage for building and another stage for running, which keeps the final image cleaner.

Builder stage

The first stage installs tools and creates the final build output.

Runtime stage

The final stage copies only what is needed to run the app and leaves build clutter behind.

Why it matters

This is one of the best ways to create smaller, cleaner production images.

Example structure

FROM node:18 AS builder
WORKDIR /app
COPY . .
RUN npm install
RUN npm run build

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

Main benefits

Smaller final images
Cleaner runtime environment
Build-only tools stay out of the final stage

Common mistakes

Copying too much from the builder stage
Installing unnecessary runtime tools again in the final stage
Not understanding what files the app actually needs at startup

Next page: Lesson 15 explains Docker Hub and registries so you can tag, push, and pull your own images properly.