Example of mounting one stage from another

Dockerfile

# syntax=docker/dockerfile:1-experimental

FROM alpine:3 AS fetcher
# We don't care about minimizing the number layers for this image.
RUN apk add --no-cache curl ca-certificates

WORKDIR /files

RUN curl -sSLf -o chronic https://github.com/docwhat/chronic/releases/download/v1.0.11/chronic_linux_amd64


FROM alpine:3 AS release
# We care about minimizing layers here.

# Documented here
# https://github.com/moby/buildkit/blob/master/frontend/dockerfile/docs/experimental.md
RUN --mount=type=bind,from=fetcher,source=/files,target=/fetcher \
      cp /fetcher/chronic /bin/chronic && \
      chown 0:0 /bin/chronic && \
      chmod a+x /bin/chronic && \
      ln -nsf chronic /bin/cronic

# EOF