What specific Dockerfile technique is used to create very small images by removing build-time tools and dependencies from the final runtime image?

The specific Dockerfile technique used to create very small images by removing build-time tools and dependencies from the final runtime image is called multi-stage builds. This technique is implemented by using multiple `FROM` instructions within a single Dockerfile, where each `FROM` statement initiates a new, independent build stage. The core idea is to separate the environment required for building an application from the environment needed solely for running it. An initial stage, often called the builder stage, utilizes a larger base image equipped with all the compilers, SDKs, and development dependencies necessary to compile, package, or process the application code. Once the desired application artifact, such as a compiled executable binary, a web application package, or a compressed bundle, is successfully generated within this builder stage, a subsequent `FROM` instruction starts a new, clean, and typically much smaller final runtime stage. In this final stage, a minimal base image is chosen, containing only the essential operating system components and any runtime libraries strictly necessary for the application to function. The critical step involves using the `COPY --from=` instruction to precisely transfer only the compiled application artifact or other specific, essential files from the earlier builder stage into this new, lightweight runtime stage. All the large build-time tools, development libraries, and temporary files that were present in the builder stage are thereby excluded from the final image. This process dramatically reduces the final image size, enhances security by minimizing the included components and potential attack surface, and improves deployment efficiency due to smaller image downloads.