Multi-stage Docker builds reduce image size by up to 80%

Docker layer caching is order-dependent: copy dependency manifests first, run install, then copy application code. Dependencies change infrequently so the cached layer eliminates rebuild time. Multi-stage builds compile in a heavy base image (node:18) and copy only artifacts to a minimal runtime image (alpine or distroless). Google's distroless images contain zero shell or package manager, reducing attack surface.