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.github/workflows | ||
closure | ||
cmd | ||
data | ||
examples | ||
nix | ||
tests | ||
types | ||
default.nix | ||
flake.lock | ||
flake.nix | ||
go.mod | ||
go.sum | ||
LICENSE | ||
main.go | ||
README.md |
nix2container
nix2container provides an efficient container development workflow with images built by Nix: it doesn't write tarballs to the Nix store and allows to skip already pushed layers (without having to rebuild them).
This is based on ideas developed in this blog post.
Getting started
{
inputs.nix2container.url = "github:nlewo/nix2container";
outputs = { self, nixpkgs, nix2container }: let
pkgs = import nixpkgs { system = "x86_64-linux"; };
nix2containerPkgs = nix2container.packages.x86_64-linux;
in {
packages.x86_64-linux.hello = nix2containerPkgs.nix2container.buildImage {
name = "hello";
config = {
entrypoint = ["${pkgs.hello}/bin/hello"];
};
};
};
}
This image can then be loaded into Docker with
$ nix run .#hello.copyToDockerDaemon
$ docker run hello:latest
Hello, world!
More Examples
To load and run the bash
example image into Podman:
$ nix run github:nlewo/nix2container#examples.bash.copyToPodman
$ podman run -it bash
bash
: Bash in/bin/
fromImage
: Alpine as base imagefromImageManifest
: Alpine as base image, from a storedmanifest.json
.nginx
nonReproducible
: with a non reproducible store path :/openbar
: set permissions on files (without root nor VM)uwsgi
: isolate dependencies in layerslayered
: build a layered image as described in this blog post
Functions documentation
nix2container.buildImage
Function arguments are:
-
name
(required): the name of the image. -
tag
(defaults to the image output hash): the tag of the image. -
config
(defaults to{}
): an attribute set describing an image configuration as defined in the OCI image specification. -
copyToRoot
(defaults tonull
): a derivation (or list of derivations) copied in the image root directory (store path prefixes/nix/store/hash-path
are removed, in order to relocate them at the image/
).pkgs.buildEnv
can be used to build a derivation which has to be copied to the image root. For instance, to get bash and coreutils in the image/bin
:copyToRoot = pkgs.buildEnv { name = "root"; paths = [ pkgs.bashInteractive pkgs.coreutils ]; pathsToLink = [ "/bin" ]; };
-
fromImage
(defaults tonull
): an image that is used as base image of this image; usepullImage
orpullImageFromManifest
to supply this. -
maxLayers
(defaults to1
): the maximum number of layers to create. This is based on the store path "popularity" as described in this blog post. Note this is applied on the image layers and not on layers added with thebuildImage.layers
attribute. -
perms
(defaults to[]
): a list of file permisssions which are set when the tar layer is created: these permissions are not written to the Nix store.Each element of this permission list is a dict such as
{ path = "a store path"; regex = ".*"; mode = "0664"; }
The mode is applied on a specific path. In this path subtree, the mode is then applied on all files matching the regex.
-
initializeNixDatabase
(defaults tofalse
): to initialize the Nix database with all store paths added into the image. Note this is only useful to run nix commands from the image, for instance to build an image used by a CI to run Nix builds. -
layers
(defaults to[]
): a list of layers built with the buildLayer function: if a store path in deps or contents belongs to one of these layers, this store path is skipped. This is pretty useful to isolate store paths that are often updated from more stable store paths, to speed up build and push time.
nix2container.pullImage
Pull an image from a container registry by name and tag/digest, storing the
entirety of the image (manifest and layer tarballs) in a single store path.
The supplied sha256
is the narhash of that store path.
Function arguments are:
-
imageName
(required): the name of the image to pull. -
imageDigest
(required): the digest of the image to pull. -
sha256
(required): the sha256 of the resulting fixed output derivation. -
os
(defaults tolinux
) -
arch
(defaults tox86_64
) -
tlsVerify
(defaults totrue
)
nix2container.pullImageFromManifest
Pull a base image from a container registry using a supplied manifest file, and the
hashes contained within it. The advantages of this over the basic pullImage
:
- Each layer archive is in its own store path, which means each will download just once and naturally deduplicate for multiple base images that share layers.
- There is no Nix-specific hash, so it's possible update the base image by simply
re-fetching the
manifest.json
from the registry; no need to actually pull the whole image just to compute a new narhash for it.
With this function the manifest.json
acts as a lockfile meant to be stored in
source control alongside the Nix container definitions. As a convenience, the manifest
can be fetched/updated using the supplied passthru script, eg:
nix run .#examples.fromImageManifest.fromImage.getManifest > examples/alpine-manifest.json
Function arguments are:
-
imageName
(required): the name of the image to pull. -
imageManifest
(required): the manifest file of the image to pull. -
imageTag
(defaults tolatest
) -
os
(defaults tolinux
) -
arch
(defaults tox86_64
) -
tlsVerify
(defaults totrue
) -
registryUrl
(defaults toregistry.hub.docker.com
)
Note that imageTag
, os
, and arch
do not affect the pulled image; that is
governed entirely by the supplied manifest.json
file. These arguments are
used for the manifest-selection logic in the included getManifest
script.
Authentication
If the Nix daemon is used for building, here is how to set up registry authentication.
docker login URL
to whatever it is- Copy
~/.docker/config.json
to/etc/nix/skopeo/auth.json
- Make the directory and all the files readable to the
nixbld
group:sudo chmod -R g+rx /etc/nix/skopeo sudo chgrp -R nixbld /etc/nix/skopeo
- Bind mount the file into the Nix build sandbox
extra-sandbox-paths = /etc/skopeo/auth.json=/etc/nix/skopeo/auth.json
Every time a new registry authentication has to be added, update
/etc/nix/skopeo/auth.json
file.
nix2container.buildLayer
For most use cases, this function is not required. However, it could be
useful to explicitly isolate some parts of the image in dedicated
layers, for caching (see the "Isolate dependencies in dedicated
layers" section) or non reproducibility (see the reproducible
argument) purposes.
Function arguments are:
-
deps
(defaults to[]
): a list of store paths to include in the layer. -
copyToRoot
(defaults tonull
): a derivation (or list of derivations) copied in the image root directory (store path prefixes/nix/store/hash-path
are removed, in order to relocate them at the image/
).pkgs.buildEnv
can be used to build a derivation which has to be copied to the image root. For instance, to get bash and coreutils in the image/bin
:copyToRoot = pkgs.buildEnv { name = "root"; paths = [ pkgs.bashInteractive pkgs.coreutils ]; pathsToLink = [ "/bin" ]; };
-
reproducible
(defaults totrue
): Iffalse
, the layer tarball is stored in the store path. This is useful when the layer dependencies are not bit reproducible: it allows to have the layer tarball and its hash in the same store path. -
maxLayers
(defaults to1
): the maximum number of layers to create. This is based on the store path "popularity" as described in this blog post. Note this is applied on the image layers and not on layers added with thebuildLayer.layers
attribute. -
perms
(defaults to[]
): a list of file permisssions which are set when the tar layer is created: these permissions are not written to the Nix store.Each element of this permission list is a dict such as
{ path = "a store path"; regex = ".*"; mode = "0664"; }
The mode is applied on a specific path. In this path subtree, the mode is then applied on all files matching the regex.
-
layers
(defaults to[]
): a list of layers built with thebuildLayer
function: if a store path in deps or contents belongs to one of these layers, this store path is skipped. This is pretty useful to isolate store paths that are often updated from more stable store paths, to speed up build and push time. -
ignore
(defaults tonull
): a store path to ignore when building the layer. This is mainly useful to ignore the configuration file from the container layer.
Isolate dependencies in dedicated layers
It is possible to isolate application dependencies in a dedicated layer. This layer is built by its own derivation: if storepaths composing this layer don't change, the layer is not rebuilt. Moreover, Skopeo can avoid to push this layer if it has already been pushed.
Let's consider an application
printing a conversation. This script
depends on bash
and the hello
binary. Because most of the changes
concern the script itself, it would be nice to isolate scripts
dependencies in a dedicated layer: when we modify the script, we only
need to rebuild and push the layer containing the script. The layer
containing dependencies won't be rebuilt and pushed.
As shown below, the buildImage.layers
attribute allows to
explicitly specify a set of dependencies to isolate.
{ pkgs }:
let
application = pkgs.writeScript "conversation" ''
${pkgs.hello}/bin/hello
echo "Haaa aa... I'm dying!!!"
'';
in
pkgs.nix2container.buildImage {
name = "hello";
config = {
entrypoint = ["${pkgs.bash}/bin/bash" application];
};
layers = [
(pkgs.nix2container.buildLayer { deps = [pkgs.bash pkgs.hello]; })
];
}
This image contains 2 layers: a layer with bash
and hello
closures
and a second layer containing the script only.
In real life, the isolated layer can contains a Python environment or Node modules.
See Nix & Docker: Layer explicitly without duplicate packages! for learning how to avoid duplicate store paths in your explicitly layered images.
Quick and dirty benchmarks
The main goal of nix2container is to provide fast rebuild/push
container cycles. In the following, we provide an order of magnitude
of rebuild and repush time, for the uwsgi
image.
warning: this is quick and dirty benchmarks which only provide an order of magnitude
We build the container and push the container. We then made a small
change in the hello.py
file to trigger a rebuild and a push.
Method | Rebuild/repush time | Executed command |
---|---|---|
nix2container.buildImage | ~1.8s | nix run .#example.uwsgi.copyToRegistry |
dockerTools.streamLayeredImage | ~7.5s | nix build .#example.uwsgi | docker load |
dockerTools.buildImage | ~10s | nix build .#example.uwsgi; skopeo copy docker-archive://./result docker://localhost:5000/uwsgi:latest |
Note we could not compare the same distribution mechanisms because
- Skopeo is not able to skip already loaded layers by the Docker daemon and
- Skopeo failed to push to the registry an image streamed to stdin.
Run the tests
nix run .#tests.all
This builds several example images with Nix, loads them with Skopeo, runs them with Podman, and test output logs.
Not that, unfortunately, these tests are not executed in the Nix sandbox because it is currently not possible to run a container in the Nix sandbox.
It is also possible to run a specific test:
nix run .#tests.basic
The nix2container Go library
This library is currently used by the Skopeo nix
transport available
in this branch.
For more information, refer to the Go documentation.