Implement cache using docker's --cache-from flag

With docker 1.13 a new build flag was added: --cache-from
This flag deprecated the buildcache tool that we used with docker 1.12

Details: moby/moby#26839

Dockerfile

@@ -3,8 +3,6 @@ FROM concourse/buildroot:iptables
 ADD docker/ /usr/local/bin/
 RUN /usr/local/bin/docker --version
 
-ADD buildcache /usr/local/bin/buildcache
-
 ADD assets/ /opt/resource/
 
 ADD ecr-login /usr/local/bin/docker-credential-ecr-login

README.md

@@ -137,12 +137,6 @@ version is the image's digest.
   first pull `image:tag` from the Docker registry (so as to use cached
   intermediate images when building). This will cause the resource to fail
   if it is set to `true` and the image does not exist yet.
-  Note: Since docker 1.10 docker images [do not contain all necessary metadata to
-  restore the build cache](https://github.com/docker/docker/issues/20316).
-  Additional metadata needs to be saved and re-applied after a docker pull to have 
-  subsequent builds skip identical intermediate layers. This additional
-  metadata is stored as a very small separate image (`image:${cache_tag}-buildcache`)
-  in the repository of this resource.
 
 * `cache_tag`: *Optional.* Default `tag`. The specific tag to pull before
   building when `cache` parameter is set. Instead of pulling the same tag

assets/out

@@ -115,13 +115,10 @@ elif [ -n "$build" ]; then
       "$(cat "${load_base}/repository"):$(cat "${load_base}/tag")"
   fi
 
+  cache_from=""
   if [ "$cache" = "true" ]; then
     docker_pull "${repository}:${cache_tag}"
-    docker create \
-      --cidfile=/tmp/container.cid \
-      "${repository}:${cache_tag}-buildcache" whatever && \
-      docker cp $(cat /tmp/container.cid):/buildcache.tgz /tmp/buildcache.tgz && \
-      docker load -i /tmp/buildcache.tgz
+    cache_from="--cache-from ${repository}:${cache_tag}"
   fi
 
   expanded_build_args=""
@@ -133,7 +130,7 @@ elif [ -n "$build" ]; then
     expanded_build_args=${expanded_build_args}" "$(jq -r 'with_entries(.key |= "--build-arg " + . )|with_entries(.key = .key + "=" +.value)|keys|join(" ")' <$build_args_file)
   fi
 
-  docker build -t "${repository}:${tag_name}" $expanded_build_args -f "$dockerfile" "$build"
+  docker build -t "${repository}:${tag_name}" $expanded_build_args -f "$dockerfile" $cache_from "$build"
 elif [ -n "$load_file" ]; then
   if [ -n "$load_repository" ]; then
     docker load -i "$load_file"
@@ -181,12 +178,6 @@ if [ "$need_tag_as_latest" = "true" ] && [ "${tag_name}" != "latest"  ]    ; the
   echo "${repository}:${tag_name} tagged as latest"
 fi
 
-if [ -n "$build" ] && [ "$cache" = "true" ]; then
-  buildcache save -o buildcache.tgz "${repository}:${tag_name}"
-  tar c buildcache.tgz | docker import - "${repository}:${cache_tag}-buildcache"
-  docker push "${repository}:${cache_tag}-buildcache"
-fi
-
 jq -n "{
   version: {
     digest: $(echo $digest | jq -R .)

ci/scripts/build

@@ -20,8 +20,6 @@ go build -o ./assets/print-metadata ./cmd/print-metadata/
 
 curl -sSL -O "https://get.docker.com/builds/Linux/x86_64/docker-${DOCKER_VERSION}.tgz"
 tar zxf "docker-${DOCKER_VERSION}.tgz"
-go build -o ./buildcache github.com/concourse/docker-image-resource/vendor/github.com/tonistiigi/buildcache/cmd/buildcache
-
 
 go build -o ./ecr-login github.com/concourse/docker-image-resource/vendor/github.com/awslabs/amazon-ecr-credential-helper/ecr-login/cmd
 

scripts/deps

@@ -3,5 +3,4 @@
 godep save \
   ./... \
   github.com/onsi/ginkgo/ginkgo \
-  github.com/awslabs/amazon-ecr-credential-helper/ecr-login/cmd \
-  github.com/tonistiigi/buildcache/cmd/buildcache
+  github.com/awslabs/amazon-ecr-credential-helper/ecr-login/cmd