Docker Multi-Stage Build Generator

A multi-stage build uses multiple FROM statements in a single Dockerfile. Each stage has its own filesystem and can copy specific artifacts from previous stages. The key benefit: your final image only contains what you explicitly copy — not the build tools, compilers, or dev dependencies. This can shrink images from gigabytes to under 100MB.

COPY --from=<stage> copies files from a named or numbered stage into the current stage. Example: 'COPY --from=builder /app/dist /usr/share/nginx/html' copies the compiled output from the builder stage into an nginx image. The builder stage's filesystem (node_modules, source files, compilers) is discarded.

For Node.js, use node:20-alpine for production — it's ~50MB vs ~300MB for node:20-slim. For the build stage, node:20-alpine also works. Avoid node:latest (unpinned, large). If you need specific glibc features not in Alpine's musl, use node:20-slim instead. Always pin your versions: node:20.11-alpine3.19.

.dockerignore prevents unnecessary files from being sent to the Docker build context. Without it, Docker copies your entire project directory (including node_modules, .git, test files) before running the Dockerfile. A good .dockerignore can reduce build context from gigabytes to kilobytes, significantly speeding up builds.

Use 'worker' for background jobs, queue consumers, and scheduled tasks that don't listen on a port. Use 'api' for HTTP servers. Use 'static' for SPAs, documentation, and sites served by nginx. The distinction matters for the CMD/ENTRYPOINT, the runtime base image, and whether you need an exposed port.

Copy package.json and package-lock.json before copying source code. Docker layer caching means if those files haven't changed, the npm install layer is reused on the next build. Example order: COPY package*.json ./ → RUN npm ci → COPY . . This keeps build times fast when only code changes.