nixpkgs/doc/functions/dockertools.xml

<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>

 <warning>
  <para>
   The <varname>dockerTools</varname> API is unstable and may be subject to
   backwards-incompatible changes in the future.
  </para>
 </warning>

 <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.
  </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>
      Tag of the generated image.
     </para>
     <para>
      <emphasis>Default:</emphasis> the output path's hash
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <term>
     <varname>contents</varname> <emphasis>optional</emphasis>
    </term>
    <listitem>
     <para>
      Top level paths in the container. Either a single derivation, or a list
      of derivations.
     </para>
     <para>
      <emphasis>Default:</emphasis> <literal>[]</literal>
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <term>
     <varname>config</varname> <emphasis>optional</emphasis>
    </term>
    <listitem>
     <para>
      Run-time configuration of the container. A full list of the options are
      available at 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>
     <para>
      <emphasis>Default:</emphasis> <literal>{}</literal>
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <term>
     <varname>created</varname> <emphasis>optional</emphasis>
    </term>
    <listitem>
     <para>
      Date and time the layers were created. Follows the same
      <literal>now</literal> exception supported by
      <literal>buildImage</literal>.
     </para>
     <para>
      <emphasis>Default:</emphasis> <literal>1970-01-01T00:00:01Z</literal>
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <term>
     <varname>maxLayers</varname> <emphasis>optional</emphasis>
    </term>
    <listitem>
     <para>
      Maximum number of layers to create.
     </para>
     <para>
      <emphasis>Default:</emphasis> <literal>24</literal>
     </para>
    </listitem>
   </varlistentry>
  </variablelist>

  <section xml:id="dockerTools-buildLayeredImage-arg-contents">
   <title>Behavior of <varname>contents</varname> in the final image</title>

   <para>
    Each path directly listed in <varname>contents</varname> will have a
    symlink in the root of the image.
   </para>

   <para>
    For example:
<programlisting><![CDATA[
pkgs.dockerTools.buildLayeredImage {
  name = "hello";
  contents = [ pkgs.hello ];
}
]]></programlisting>
    will create symlinks for all the paths in the <literal>hello</literal>
    package:
<screen><![CDATA[
/bin/hello -> /nix/store/h1zb1padqbbb7jicsvkmrym3r6snphxg-hello-2.10/bin/hello
/share/info/hello.info -> /nix/store/h1zb1padqbbb7jicsvkmrym3r6snphxg-hello-2.10/share/info/hello.info
/share/locale/bg/LC_MESSAGES/hello.mo -> /nix/store/h1zb1padqbbb7jicsvkmrym3r6snphxg-hello-2.10/share/locale/bg/LC_MESSAGES/hello.mo
]]></screen>
   </para>
  </section>

  <section xml:id="dockerTools-buildLayeredImage-arg-config">
   <title>Automatic inclusion of <varname>config</varname> references</title>

   <para>
    The closure of <varname>config</varname> is automatically included in the
    closure of the final image.
   </para>

   <para>
    This allows you to make very simple Docker images with very little code.
    This container will start up and run <command>hello</command>:
<programlisting><![CDATA[
pkgs.dockerTools.buildLayeredImage {
  name = "hello";
  config.Cmd = [ "${pkgs.hello}/bin/hello" ];
}
]]></programlisting>
   </para>
  </section>

  <section xml:id="dockerTools-buildLayeredImage-arg-maxLayers">
   <title>Adjusting <varname>maxLayers</varname></title>

   <para>
    Increasing the <varname>maxLayers</varname> increases the number of layers
    which have a chance to be shared between different images.
   </para>

   <para>
    Modern Docker installations support up to 128 layers, however older
    versions support as few as 42.
   </para>

   <para>
    If the produced image will not be extended by other Docker builds, it is
    safe to set <varname>maxLayers</varname> to <literal>128</literal>. However
    it will be impossible to extend the image further.
   </para>

   <para>
    The first (<literal>maxLayers-2</literal>) most "popular" paths will have
    their own individual layers, then layer #<literal>maxLayers-1</literal>
    will contain all the remaining "unpopular" paths, and finally layer
    #<literal>maxLayers</literal> will contain the Image configuration.
   </para>

   <para>
    Docker's Layers are not inherently ordered, they are content-addressable
    and are not explicitly layered until they are composed in to an Image.
   </para>
  </section>
 </section>

 <section xml:id="ssec-pkgs-dockerTools-fetchFromRegistry">
  <title>pullImage</title>

  <para>
   This function is analogous to the <command>docker pull</command> command, in
   that it can be used to pull a Docker image from a Docker registry. By default
   <link xlink:href="https://hub.docker.com/">Docker Hub</link> is used to pull
   images.
  </para>

  <para>
   Its parameters are described in the example below:
  </para>

  <example xml:id='ex-dockerTools-pullImage'>
   <title>Docker pull</title>
<programlisting>
pullImage {
  imageName = "nixos/nix"; <co xml:id='ex-dockerTools-pullImage-1' />
  imageDigest = "sha256:20d9485b25ecfd89204e843a962c1bd70e9cc6858d65d7f5fadc340246e2116b"; <co xml:id='ex-dockerTools-pullImage-2' />
  finalImageTag = "1.11";  <co xml:id='ex-dockerTools-pullImage-3' />
  sha256 = "0mqjy3zq2v6rrhizgb9nvhczl87lcfphq9601wcprdika2jz7qh8"; <co xml:id='ex-dockerTools-pullImage-4' />
  os = "linux"; <co xml:id='ex-dockerTools-pullImage-5' />
  arch = "x86_64"; <co xml:id='ex-dockerTools-pullImage-6' />
}
</programlisting>
  </example>

  <calloutlist>
   <callout arearefs='ex-dockerTools-pullImage-1'>
    <para>
     <varname>imageName</varname> specifies the name of the image to be
     downloaded, which can also include the registry namespace (e.g.
     <literal>nixos</literal>). This argument is required.
    </para>
   </callout>
   <callout arearefs='ex-dockerTools-pullImage-2'>
    <para>
     <varname>imageDigest</varname> specifies the digest of the image to be
     downloaded. Skopeo can be used to get the digest of an image, with its
     <varname>inspect</varname> subcommand. Since a given
     <varname>imageName</varname> may transparently refer to a manifest list of
     images which support multiple architectures and/or operating systems,
     supply the `--override-os` and `--override-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.
<programlisting>
$ nix-shell --packages skopeo jq --command "skopeo --override-os linux --override-arch x86_64 inspect docker://docker.io/nixos/nix:1.11 | jq -r '.Digest'"
sha256:20d9485b25ecfd89204e843a962c1bd70e9cc6858d65d7f5fadc340246e2116b
</programlisting>
     This argument is required.
    </para>
   </callout>
   <callout arearefs='ex-dockerTools-pullImage-3'>
    <para>
     <varname>finalImageTag</varname>, 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
     <literal>latest</literal>.
    </para>
   </callout>
   <callout arearefs='ex-dockerTools-pullImage-4'>
    <para>
     <varname>sha256</varname> is the checksum of the whole fetched image. This
     argument is required.
    </para>
   </callout>
   <callout arearefs='ex-dockerTools-pullImage-5'>
    <para>
     <varname>os</varname>, if specified, is the operating system of the
     fetched image. By default it's <literal>linux</literal>.
    </para>
   </callout>
   <callout arearefs='ex-dockerTools-pullImage-6'>
    <para>
     <varname>arch</varname>, if specified, is the cpu architecture of the
     fetched image. By default it's <literal>x86_64</literal>.
    </para>
   </callout>
  </calloutlist>
 </section>

 <section xml:id="ssec-pkgs-dockerTools-exportImage">
  <title>exportImage</title>

  <para>
   This function is analogous to the <command>docker export</command> 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 <command>docker
   import</command>.
  </para>

  <note>
   <para>
    Using this function requires the <literal>kvm</literal> device to be
    available.
   </para>
  </note>

  <para>
   The parameters of <varname>exportImage</varname> are the following:
  </para>

  <example xml:id='ex-dockerTools-exportImage'>
   <title>Docker export</title>
<programlisting>
exportImage {
  fromImage = someLayeredImage;
  fromImageName = null;
  fromImageTag = null;

  name = someLayeredImage.name;
}
  </programlisting>
  </example>

  <para>
   The parameters relative to the base image have the same synopsis as
   described in <xref linkend='ssec-pkgs-dockerTools-buildImage'/>, except that
   <varname>fromImage</varname> is the only required argument in this case.
  </para>

  <para>
   The <varname>name</varname> argument is the name of the derivation output,
   which defaults to <varname>fromImage.name</varname>.
  </para>
 </section>

 <section xml:id="ssec-pkgs-dockerTools-shadowSetup">
  <title>shadowSetup</title>

  <para>
   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 <varname>runAsRoot</varname>
   <xref linkend='ex-dockerTools-buildImage-runAsRoot'/> script for cases like
   in the example below:
  </para>

  <example xml:id='ex-dockerTools-shadowSetup'>
   <title>Shadow base files</title>
<programlisting>
buildImage {
  name = "shadow-basic";

  runAsRoot = ''
    #!${pkgs.runtimeShell}
    ${shadowSetup}
    groupadd -r redis
    useradd -r -g redis redis
    mkdir /data
    chown redis:redis /data
  '';
}
</programlisting>
  </example>

  <para>
   Creating base files like <literal>/etc/passwd</literal> or
   <literal>/etc/login.defs</literal> is necessary for shadow-utils to
   manipulate users and groups.
  </para>
 </section>
</section>