Single layer docker image with build artifacts

Dockerfile

FROM alpine:latest AS builder
RUN echo "foo" > /foo.txt

FROM scratch
COPY --from=builder /*.txt .

Shell

pkhuong@penguin:/tmp/docker-hack$ docker -v
Docker version 19.03.3-beta2, build dede96ff4c
pkhuong@penguin:/tmp/docker-hack$ docker build .
Sending build context to Docker daemon  2.048kB
Step 1/4 : FROM alpine:latest AS builder
latest: Pulling from library/alpine
9d48c3bd43c5: Pull complete 
Digest: sha256:72c42ed48c3a2db31b7dafe17d275b634664a708d901ec9fd57b1529280f01fb
Status: Downloaded newer image for alpine:latest
 ---> 961769676411
Step 2/4 : RUN echo "foo" > /foo.txt
 ---> Running in ae75064a947b
Removing intermediate container ae75064a947b
 ---> ef6c6067c3e2
Step 3/4 : FROM scratch
 ---> 
Step 4/4 : COPY --from=builder /*.txt .
 ---> e61754c79a6b
Successfully built e61754c79a6b
pkhuong@penguin:/tmp/docker-hack$ docker save e61754c79a6b > test.tar
pkhuong@penguin:/tmp/docker-hack$ mkdir test
pkhuong@penguin:/tmp/docker-hack$ cd test
pkhuong@penguin:/tmp/docker-hack/test$ tar -xf ../test.tar
pkhuong@penguin:/tmp/docker-hack/test$ ls
07901039823771394504e93342ba3fce4d42bf59ebbed88091fda9175fba4af7  e61754c79a6bd2012097a7663013b7f0b7dff75afc7bac5bd4120a09657996f1.json  manifest.json
pkhuong@penguin:/tmp/docker-hack/test$ mkdir -p /tmp/docker-hack/layer; cd /tmp/docker-hack/layer
pkhuong@penguin:/tmp/docker-hack/layer$ tar -xf ../test/07901039823771394504e93342ba3fce4d42bf59ebbed88091fda9175fba4af7/layer.tar 
pkhuong@penguin:/tmp/docker-hack/layer$ ls
foo.txt
pkhuong@penguin:/tmp/docker-hack/layer$ cat foo.txt
foo