What is a multi-stage build and why use one?

A multi-stage build uses multiple FROM instructions in one Dockerfile, each starting a new, independent build stage. Later stages can selectively COPY artifacts from earlier stages using COPY --from=<stage>. This lets you use a full SDK/build-toolchain image to compile your application, then discard that entire toolchain in the final stage, copying only the compiled artifact into a minimal runtime base image — dramatically shrinking final image size and attack surface.