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<section xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:xi="http://www.w3.org/2001/XInclude"
xml:id="sec-pkgs-dockerTools">
<title>pkgs.dockerTools</title>
<para>
<varname>pkgs.dockerTools</varname> is a set of functions for creating and manipulating Docker images according to the <link xlink:href="https://github.com/moby/moby/blob/master/image/spec/v1.2.md#docker-image-specification-v120"> Docker Image Specification v1.2.0 </link>. Docker itself is not used to perform any of the operations done by these functions.
</para>
<section xml:id="ssec-pkgs-dockerTools-buildImage">
<title>buildImage</title>
<para>
This function is analogous to the <command>docker build</command> 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 <command>docker load</command>.
</para>
<para>
The parameters of <varname>buildImage</varname> with relative example values are described below:
</para>
<example xml:id='ex-dockerTools-buildImage'>
<title>Docker build</title>
<programlisting>
buildImage {
name = "redis"; <co xml:id='ex-dockerTools-buildImage-1' />
tag = "latest"; <co xml:id='ex-dockerTools-buildImage-2' />
fromImage = someBaseImage; <co xml:id='ex-dockerTools-buildImage-3' />
fromImageName = null; <co xml:id='ex-dockerTools-buildImage-4' />
fromImageTag = "latest"; <co xml:id='ex-dockerTools-buildImage-5' />
contents = pkgs.redis; <co xml:id='ex-dockerTools-buildImage-6' />
runAsRoot = '' <co xml:id='ex-dockerTools-buildImage-runAsRoot' />
#!${pkgs.runtimeShell}
mkdir -p /data
'';
config = { <co xml:id='ex-dockerTools-buildImage-8' />
Cmd = [ "/bin/redis-server" ];
WorkingDir = "/data";
Volumes = {
"/data" = {};
};
};
}
</programlisting>
</example>
<para>
The above example will build a Docker image <literal>redis/latest</literal> from the given base image. Loading and running this image in Docker results in <literal>redis-server</literal> being started automatically.
</para>
<calloutlist>
<callout arearefs='ex-dockerTools-buildImage-1'>
<para>
<varname>name</varname> specifies the name of the resulting image. This is the only required argument for <varname>buildImage</varname>.
</para>
</callout>
<callout arearefs='ex-dockerTools-buildImage-2'>
<para>
<varname>tag</varname> specifies the tag of the resulting image. By default it's <literal>null</literal>, which indicates that the nix output hash will be used as tag.
</para>
</callout>
<callout arearefs='ex-dockerTools-buildImage-3'>
<para>
<varname>fromImage</varname> is the repository tarball containing the base image. It must be a valid Docker image, such as exported by <command>docker save</command>. By default it's <literal>null</literal>, which can be seen as equivalent to <literal>FROM scratch</literal> of a <filename>Dockerfile</filename>.
</para>
</callout>
<callout arearefs='ex-dockerTools-buildImage-4'>
<para>
<varname>fromImageName</varname> can be used to further specify the base image within the repository, in case it contains multiple images. By default it's <literal>null</literal>, in which case <varname>buildImage</varname> will peek the first image available in the repository.
</para>
</callout>
<callout arearefs='ex-dockerTools-buildImage-5'>
<para>
<varname>fromImageTag</varname> 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 <literal>null</literal>, in which case <varname>buildImage</varname> will peek the first tag available for the base image.
</para>
</callout>
<callout arearefs='ex-dockerTools-buildImage-6'>
<para>
<varname>contents</varname> is a derivation that will be copied in the new layer of the resulting image. This can be similarly seen as <command>ADD contents/ /</command> in a <filename>Dockerfile</filename>. By default it's <literal>null</literal>.
</para>
</callout>
<callout arearefs='ex-dockerTools-buildImage-runAsRoot'>
<para>
<varname>runAsRoot</varname> 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 <varname>contents</varname> derivation. This can be similarly seen as <command>RUN ...</command> in a <filename>Dockerfile</filename>.
<note>
<para>
Using this parameter requires the <literal>kvm</literal> device to be available.
</para>
</note>
</para>
</callout>
<callout arearefs='ex-dockerTools-buildImage-8'>
<para>
<varname>config</varname> 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 <link xlink:href="https://github.com/moby/moby/blob/master/image/spec/v1.2.md#image-json-field-descriptions"> Docker Image Specification v1.2.0 </link>.
</para>
</callout>
</calloutlist>
<para>
After the new layer has been created, its closure (to which <varname>contents</varname>, <varname>config</varname> and <varname>runAsRoot</varname> contribute) will be copied in the layer itself. Only new dependencies that are not already in the existing layers will be copied.
</para>
<para>
At the end of the process, only one new single layer will be produced and added to the resulting image.
</para>
<para>
The resulting repository will only list the single image <varname>image/tag</varname>. In the case of <xref linkend='ex-dockerTools-buildImage'/> it would be <varname>redis/latest</varname>.
</para>
<para>
It is possible to inspect the arguments with which an image was built using its <varname>buildArgs</varname> attribute.
</para>
<note>
<para>
If you see errors similar to <literal>getProtocolByName: does not exist (no such protocol name: tcp)</literal> you may need to add <literal>pkgs.iana-etc</literal> to <varname>contents</varname>.
</para>
</note>
<note>
<para>
If you see errors similar to <literal>Error_Protocol ("certificate has unknown CA",True,UnknownCa)</literal> you may need to add <literal>pkgs.cacert</literal> to <varname>contents</varname>.
</para>
</note>
<example xml:id="example-pkgs-dockerTools-buildImage-creation-date">
<title>Impurely Defining a Docker Layer's Creation Date</title>
<para>
By default <function>buildImage</function> will use a static date of one second past the UNIX Epoch. This allows <function>buildImage</function> to produce binary reproducible images. When listing images with <command>docker images</command>, the newly created images will be listed like this:
</para>
<screen><![CDATA[
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
hello latest 08c791c7846e 48 years ago 25.2MB
]]></screen>
<para>
You can break binary reproducibility but have a sorted, meaningful <literal>CREATED</literal> column by setting <literal>created</literal> to <literal>now</literal>.
</para>
<programlisting><![CDATA[
pkgs.dockerTools.buildImage {
name = "hello";
tag = "latest";
created = "now";
contents = pkgs.hello;
config.Cmd = [ "/bin/hello" ];
}
]]></programlisting>
<para>
and now the Docker CLI will display a reasonable date and sort the images as expected:
<screen><![CDATA[
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
hello latest de2bf4786de6 About a minute ago 25.2MB
]]></screen>
however, the produced images will not be binary reproducible.
</para>
</example>
</section>
<section xml:id="ssec-pkgs-dockerTools-buildLayeredImage">
<title>buildLayeredImage</title>
<para>
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 <function>streamLayeredImage</function> instead, which this function uses internally.
</para>
<variablelist>
<varlistentry>
<term>
<varname>name</varname>
</term>
<listitem>
<para>
The name of the resulting image.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>tag</varname> <emphasis>optional</emphasis>
</term>
<listitem>
<para><
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