COPY --from is usually shown pointing at an earlier stage, and it accepts an image name just as happily — which removes a whole class of “install this one binary” instruction.
FROM php:7.1-fpm
# no curl, no gpg, no checksum to keep up to date
COPY --from=composer:1.5 /usr/bin/composer /usr/bin/composerThe version is pinned by the image tag, so upgrading is a one-line change and the provenance is whoever publishes that image rather than a URL in a RUN. It also skips the intermediate layer that downloading and deleting an installer would leave behind. Worth using for anything published as an official image; not worth it for something you would then have to trust blindly.