# Multi-Stage Builds — Docker

Source: https://www.geekswithgeeks.com/en/docker/docker-multi-stage-builds

> Compile in one stage, ship only the runtime artifacts in a smaller final image.

## Why bother?

Build tools, compilers, and source code often aren't needed at runtime, but a single-stage Dockerfile ships them anyway — bloating the image and its attack surface.

## Build stage + runtime stage

Name a stage with `AS`, then `COPY --from=<stage>` pulls only the built artifact into a slim final image — the compiler and dev dependencies never make it in.

```dockerfile
# --- build stage ---
FROM node:20 AS build
WORKDIR /app
COPY . .
RUN npm install && npm run build

# --- runtime stage ---
FROM node:20-alpine
WORKDIR /app
COPY --from=build /app/dist ./dist
COPY package.json .
RUN npm install --production
CMD ["node", "dist/server.js"]
```