$ git clone git://github.com/matejc/push
$ cd ./push
$ nix-build

$ nix-build test_image.nix -o image.tar.gz
these derivations will be built:
  /nix/store/xg5g57px4jcr005fbk72s4brsqzpvymw-my-echo-config.json.drv
  /nix/store/fk8giwrv2yysac8ny8449vpf3v5ximny-docker-layer.drv
  /nix/store/ccqql37jb5i5nivc9kb4rz6c2ikf7gkx-runtime-deps.drv
  /nix/store/r21k9nszvi7c6bgvk63358385mj9yrpv-my-echo.tar.gz.drv
building path(s) ‘/nix/store/83045vj35r5cajsk375j54fl2hq7ai3a-my-echo-config.json’
building path(s) ‘/nix/store/yczixa8m6q1jy883rpd8na6rss70q3pm-docker-layer’
Adding contents
/tmp/nix-build-docker-layer.drv-0/layer /tmp/nix-build-docker-layer.drv-0
/tmp/nix-build-docker-layer.drv-0
Packing layer
building path(s) ‘/nix/store/8ap63bzwwzrbmy5k6l98b17xkanz1x56-runtime-deps’
building path(s) ‘/nix/store/x5h6wr918kqwbf3gai43vbavmb3alz6q-my-echo.tar.gz’
Adding layer
Adding meta
Cooking the image
/nix/store/x5h6wr918kqwbf3gai43vbavmb3alz6q-my-echo.tar.gz

$ ./result/bin/push ./image.tar.gz http://localhost:5000
[2ed41dd] Calculating digest for layer.tar ...
[2ed41dd] Compressing layer.tar to layer.tgz ...
[2ed41dd] Calculating digest for layer.tgz ...
Registry http://localhost:5000/v2/ is OK
[my-echo:latest] Pushing 17a778a3b461 ...
[my-echo:latest] Pushed 17a778a3b461
[my-echo:latest] Pushing a8c92d823a55 ...
[my-echo:latest] Pushed a8c92d823a55
[my-echo:latest] Uploaded 9035.60 KiB
Success!
Removing /tmp/tmpp9ks3qij ...

$ docker pull localhost:5000/my-echo:latest
latest: Pulling from my-echo
c17b5508357a: Pull complete
Digest: sha256:9b4f58441d2e548e61c9353b874094493e9b797d8a548d1db163f724dc410264
Status: Downloaded newer image for localhost:5000/my-echo:latest

$ docker run -ti --rm localhost:5000/my-echo:latest
test hello!