`pkgs.dockerTools` is a set of functions for creating and manipulating Docker images according to the [Docker Image Specification v1.2.0](https://github.com/moby/moby/blob/master/image/spec/v1.2.md#docker-image-specification-v120). Docker itself is not used to perform any of the operations done by these functions.
This function is analogous to the `docker build` command, in that it can be used to build a Docker-compatible repository tarball containing a single image with one or multiple layers. As such, the result is suitable for being loaded in Docker with `docker load`.
The parameters of `buildImage` with relative example values are described below:
The above example will build a Docker image `redis/latest` from the given base image. Loading and running this image in Docker results in `redis-server` being started automatically.
-`name` specifies the name of the resulting image. This is the only required argument for `buildImage`.
-`fromImage` is the repository tarball containing the base image. It must be a valid Docker image, such as exported by `docker save`. By default it's `null`, which can be seen as equivalent to `FROM scratch` of a `Dockerfile`.
-`fromImageName` can be used to further specify the base image within the repository, in case it contains multiple images. By default it's `null`, in which case `buildImage` will peek the first image available in the repository.
-`fromImageTag` can be used to further specify the tag of the base image within the repository, in case an image contains multiple tags. By default it's `null`, in which case `buildImage` will peek the first tag available for the base image.
-`copyToRoot` is a derivation that will be copied in the new layer of the resulting image. This can be similarly seen as `ADD contents/ /` in a `Dockerfile`. By default it's `null`.
-`runAsRoot` is a bash script that will run as root in an environment that overlays the existing layers of the base image with the new resulting layer, including the previously copied `contents` derivation. This can be similarly seen as `RUN ...` in a `Dockerfile`.
> **_NOTE:_** Using this parameter requires the `kvm` device to be available.
-`config` is used to specify the configuration of the containers that will be started off the built image in Docker. The available options are listed in the [Docker Image Specification v1.2.0](https://github.com/moby/moby/blob/master/image/spec/v1.2.md#image-json-field-descriptions).
-`architecture` is _optional_ and used to specify the image architecture, this is useful for multi-architecture builds that don't need cross compiling. If not specified it will default to `hostPlatform`.
After the new layer has been created, its closure (to which `contents`, `config` and `runAsRoot` contribute) will be copied in the layer itself. Only new dependencies that are not already in the existing layers will be copied.
At the end of the process, only one new single layer will be produced and added to the resulting image.
The resulting repository will only list the single image `image/tag`. In the case of [the `buildImage` example](#ex-dockerTools-buildImage), it would be `redis/latest`.
It is possible to inspect the arguments with which an image was built using its `buildArgs` attribute.
> **_NOTE:_** If you see errors similar to `getProtocolByName: does not exist (no such protocol name: tcp)` you may need to add `pkgs.iana-etc` to `contents`.
> **_NOTE:_** If you see errors similar to `Error_Protocol ("certificate has unknown CA",True,UnknownCa)` you may need to add `pkgs.cacert` to `contents`.
By default `buildImage` will use a static date of one second past the UNIX Epoch. This allows `buildImage` to produce binary reproducible images. When listing images with `docker images`, the newly created images will be listed like this:
```ShellSession
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
hello latest 08c791c7846e 48 years ago 25.2MB
```
You can break binary reproducibility but have a sorted, meaningful `CREATED` column by setting `created` to `now`.
Create a Docker image with many of the store paths being on their own layer to improve sharing between images. The image is realized into the Nix store as a gzipped tarball. Depending on the intended usage, many users might prefer to use `streamLayeredImage` instead, which this function uses internally.
`architecture` is _optional_ and used to specify the image architecture, this is useful for multi-architecture builds that don't need cross compiling. If not specified it will default to `hostPlatform`.
: Run-time configuration of the container. A full list of the options are available at in the [Docker Image Specification v1.2.0](https://github.com/moby/moby/blob/master/image/spec/v1.2.md#image-json-field-descriptions).
: Shell commands to run while building the final layer, without access to most of the layer contents. Changes to this layer are "on top" of all the other layers, so can create additional directories and files.
: Shell commands to run while creating the archive for the final layer in a fakeroot environment. Unlike `extraCommands`, you can run `chown` to change the owners of the files in the archive, changing fakeroot's state instead of the real filesystem. The latter would require privileges that the build user does not have. Static binaries do not interact with the fakeroot environment. By default all files in the archive will be owned by root.
: Whether to run in `fakeRootCommands` in `fakechroot`, making programs behave as though `/` is the root of the image being created, while files in the Nix store are available as usual. This allows scripts that perform installation in `/` to work as expected. Considering that `fakechroot` is implemented via the same mechanism as `fakeroot`, the same caveats apply.
If the produced image will not be extended by other Docker builds, it is safe to set `maxLayers` to `128`. However, it will be impossible to extend the image further.
The first (`maxLayers-2`) most "popular" paths will have their own individual layers, then layer \#`maxLayers-1` will contain all the remaining "unpopular" paths, and finally layer \#`maxLayers` will contain the Image configuration.
Builds a script which, when run, will stream an uncompressed tarball of a Docker image to stdout. The arguments to this function are as for `buildLayeredImage`. This method of constructing an image does not realize the image into the Nix store, so it saves on IO and disk/cache space, particularly with large images.
The image produced by running the output script can be piped directly into `docker load`, to load it into the local docker daemon:
This function is analogous to the `docker pull` command, in that it can be used to pull a Docker image from a Docker registry. By default [Docker Hub](https://hub.docker.com/) is used to pull images.
Its parameters are described in the example below:
-`imageName` specifies the name of the image to be downloaded, which can also include the registry namespace (e.g. `nixos`). This argument is required.
-`imageDigest` specifies the digest of the image to be downloaded. This argument is required.
-`finalImageName`, if specified, this is the name of the image to be created. Note it is never used to fetch the image since we prefer to rely on the immutable digest ID. By default it's equal to `imageName`.
-`finalImageTag`, if specified, this is the tag of the image to be created. Note it is never used to fetch the image since we prefer to rely on the immutable digest ID. By default it's `latest`.
`nix-prefetch-docker` command can be used to get required image parameters:
```ShellSession
$ nix run nixpkgs.nix-prefetch-docker -c nix-prefetch-docker --image-name mysql --image-tag 5
```
Since a given `imageName` may transparently refer to a manifest list of images which support multiple architectures and/or operating systems, you can supply the `--os` and `--arch` arguments to specify exactly which image you want. By default it will match the OS and architecture of the host the command is run on.
```ShellSession
$ nix-prefetch-docker --image-name mysql --image-tag 5 --arch x86_64 --os linux
```
Desired image name and tag can be set using `--final-image-name` and `--final-image-tag` arguments:
```ShellSession
$ nix-prefetch-docker --image-name mysql --image-tag 5 --final-image-name eu.gcr.io/my-project/mysql --final-image-tag prod
This function is analogous to the `docker export` command, in that it can be used to flatten a Docker image that contains multiple layers. It is in fact the result of the merge of all the layers of the image. As such, the result is suitable for being imported in Docker with `docker import`.
> **_NOTE:_** Using this function requires the `kvm` device to be available.
The parameters of `exportImage` are the following:
```nix
exportImage {
fromImage = someLayeredImage;
fromImageName = null;
fromImageTag = null;
name = someLayeredImage.name;
}
```
The parameters relative to the base image have the same synopsis as described in [buildImage](#ssec-pkgs-dockerTools-buildImage), except that `fromImage` is the only required argument in this case.
The `name` argument is the name of the derivation output, which defaults to `fromImage.name`.
This constant string is a helper for setting up the base files for managing users and groups, only if such files don't exist already. It is suitable for being used in a [`buildImage` `runAsRoot`](#ex-dockerTools-buildImage-runAsRoot) script for cases like in the example below:
Create a Docker image that sets up an environment similar to that of running `nix-shell` on a derivation.
When run in Docker, this environment somewhat resembles the Nix sandbox typically used by `nix-build`, with a major difference being that access to the internet is allowed.
It additionally also behaves like an interactive `nix-shell`, running things like `shellHook` and setting an interactive prompt.
If the derivation is fully buildable (i.e. `nix-build` can be used on it), running `buildDerivation` inside such a Docker image will build the derivation, with all its outputs being available in the correct `/nix/store` paths, pointed to by the respective environment variables like `$out`, etc.
::: {.warning}
The behavior doesn't match `nix-shell` or `nix-build` exactly and this function is known not to work correctly for e.g. fixed-output derivations, content-addressed derivations, impure derivations and other special types of derivations.
:::
### Arguments
`drv`
: The derivation on which to base the Docker image.
Adding packages to the Docker image is possible by e.g. extending the list of `nativeBuildInputs` of this derivation like
```nix
buildNixShellImage {
drv = someDrv.overrideAttrs (old: {
nativeBuildInputs = old.nativeBuildInputs or [] ++ [
somethingExtra
];
});
# ...
}
```
Similarly, you can extend the image initialization script by extending `shellHook`
`name`_optional_
: The name of the resulting image.
*Default:*`drv.name + "-env"`
`tag`_optional_
: Tag of the generated image.
*Default:* the resulting image derivation output path's hash
`uid`/`gid` _optional_
: The user/group ID to run the container as. This is like a `nixbld` build user.
*Default:* 1000/1000
`homeDirectory`_optional_
: The home directory of the user the container is running as
*Default:*`/build`
`shell`_optional_
: The path to the `bash` binary to use as the shell. This shell is started when running the image.
*Default:*`pkgs.bashInteractive + "/bin/bash"`
`command`_optional_
: Run this command in the environment of the derivation, in an interactive shell. See the `--command` option in the [`nix-shell` documentation](https://nixos.org/manual/nix/stable/command-ref/nix-shell.html?highlight=nix-shell#options).
*Default:* (none)
`run`_optional_
: Same as `command`, but runs the command in a non-interactive shell instead. See the `--run` option in the [`nix-shell` documentation](https://nixos.org/manual/nix/stable/command-ref/nix-shell.html?highlight=nix-shell#options).
*Default:* (none)
### Example
The following shows how to build the `pkgs.hello` package inside a Docker container built with `buildNixShellImage`.