git init

.gitignore

+# editors
+*~
+.*.sw[op]
+
+# artifacts
+*.tar*

Makefile

+.PHONY: all clean
+
+all:
+	$(MAKE) -C stretch
+
+clean:
+	$(MAKE) -C stretch clean

stretch/Dockerfile

+FROM scratch
+ADD root.tar.xz /
+CMD ["bash"]

stretch/Makefile

+# config this for image updates
+DOWNLOAD_VERSION := 2018-06-29-03:25
+DOWNLOAD_CHECKSUM := c79fa57cf66a9064addda899653178eb55cd3cc05c70c38cfa761692d742b3cc7410a057cb7010ace2116f149481f36f57513c1aca7a0d6f0fdf349e18c450e7
+
+REPO := raspbian-base
+
+DOWNLOAD_TARBALL := https://downloads.raspberrypi.org/raspbian_lite/archive/$(DOWNLOAD_VERSION)/root.tar.xz
+DOWNLOAD_FILE := root.tar.xz
+
+IMAGE_PREFIX := ${DOCKER_IMAGE_PREFIX}
+ifeq ($(IMAGE_PREFIX),)
+IMAGE_PREFIX := icinga/$(REPO)/
+endif
+
+REGISTRY := ${DOCKER_REGISTRY}
+ifneq ($(REGISTRY),)
+IMAGE_PREFIX := $(REGISTRY)/$(IMAGE_PREFIX)
+endif
+
+#ifeq ($(VERSION),)
+#VERSION := $(shell basename `pwd`)
+#endif
+VERSION := stretch
+IMAGE := $(IMAGE_PREFIX)$(VERSION)
+
+.PHONY: all download clean
+
+all: download build
+
+download: $(DOWNLOAD_FILE)
+
+$(DOWNLOAD_FILE):
+	@echo "Downloading $(DOWNLOAD_TARBALL)"
+	curl -LS -C - "$(DOWNLOAD_TARBALL)" -o "$@.tmp"
+	echo "$(DOWNLOAD_CHECKSUM)  $@.tmp" | sha512sum -c
+	mv "$@.tmp" "$@"
+
+build:
+	docker build --tag "$(IMAGE)" .
+
+push:
+	docker push "$(IMAGE)"
+
+clean:
+	rm -f *.tar*
+	if (docker inspect --type image "$(IMAGE)" >/dev/null 2>&1); then docker rmi "$(IMAGE)"; fi