The hocker package provides a small set of utilities to fetch docker image
artifacts from docker registries and produce Nix derivations marrying docker and
Nix elegantly:
hocker-imagefor fetching a docker imagehocker-layerfor fetching a docker image's layershocker-configfor fetching a docker image's configuration JSONhocker-manifestfor fetching a docker registry image manifestdocker2nixfor generating Nix expressions calling thefetchdockerderivations, given a docker registry image manifest
These tools only work with version 2 of the docker registry and docker (>=) v1.10.
The motivation for this tool came from a need to fetch docker image artifacts from a docker registry without the stock docker tooling designed to only work with the docker daemon.
Our use case (and the reason why this package exposes a docker2nix tool) is pulling
docker images into a NixOS system's store and
loading those images from the store into the docker daemon running on that same system.
We desired this for two critical reasons:
- The docker daemon no longer required an internet connection in order to load the docker images
- By virtue of fetching the docker images at build-time as opposed to run-time, failures from non-existent images or image tags are caught earlier
We strived to make this tool useful outside of the context of Nix and NixOS, therefore all of these tools are usable without Nix in the workflow.
For high-level documentation of each utility, please refer to the README's in their respective directories (links are in the above list).
Let's first retrieve a docker registry image manifest for the debian:jessie
docker image (note that we need the library/ repository prefix because we are
pulling from the official debian repository!):
$ hocker-manifest library/debian jessie
{
"schemaVersion": 2,
"mediaType": "application/vnd.docker.distribution.manifest.v2+json",
"config": {
"mediaType": "application/vnd.docker.container.image.v1+json",
"size": 1528,
"digest": "sha256:054abe38b1e6f863befa4258cbfaf127b1cc9440d2e2e349b15d22e676b591e7"
},
"layers": [
{
"mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
"size": 52550276,
"digest": "sha256:cd0a524342efac6edff500c17e625735bbe479c926439b263bbe3c8518a0849c"
}
]
}Next, we can easily generate a fetchdocker derivation using docker2nix:
$ hocker-manifest library/debian jessie | docker2nix library/debian jessie
{ fetchDockerConfig, fetchDockerLayer, fetchdocker }:
fetchdocker rec {
name = "debian";
registry = "https://registry-1.docker.io/v2/";
repository = "library";
imageName = "debian";
tag = "jessie";
imageConfig = fetchDockerConfig {
inherit tag registry repository imageName;
sha256 = "1rwinmvfc8jxn54y7qnj82acrc97y7xcnn22zaz67y76n4wbwjh5";
};
imageLayers = let
layer0 = fetchDockerLayer {
inherit registry repository imageName;
layerDigest = "cd0a524342efac6edff500c17e625735bbe479c926439b263bbe3c8518a0849c";
sha256 = "1744l0c8ag5y7ck9nhr6r5wy9frmaxi7xh80ypgnxb7g891m42nd";
};
in [ layer0 ];
}We developed these tools with private registries in-mind and they currently support three modes of authentication:
- Nothing at all (simply do not supply
--tokenor--usernameand--password) - Bearer token-based authentication, you should retrieve a token and then give
it via the
--tokenflag - Basic authentication with
--usernameand--password(most common with nginx proxied registries providing basic auth protection; you should be careful to ensure you're only sending requests to registries exposed via TLS or SSL!)
A caveat to #1 if you do not supply any authentication credential flags and you
also do not supply a --registry flag then the tools assume you wish to make a
request to the public docker hub registry, in which case they ask for a
short-lived authentication token from the registry auth server and then make the
request to the public docker hub registry.
Building (and developing a patch for) this project using cabal is
straight-forward if we have Nix installed:
$ nix-shell
[nix-shell:]$ cabal --version
cabal-install version 1.24.0.2
compiled using version 1.24.2.0 of the Cabal library... cabal and all of the package dependencies will be in the shell environment
so that we can then:
[nix-shell:]$ cabal buildAlternatively we can nix-build the project, this is not recommended for
development because Nix will not build the project incrementally:
$ nix-build --attr hocker release.nix
these derivations will be built:
/nix/store/3dwvcm66360fpfqrrc4swp9y4q0jzvh9-hocker-0.1.0.0.drv
building path(s) ‘/nix/store/g16mrfhlmb1z3qkdzr0diaqn2dhl8bv6-hocker-0.1.0.0’
...
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