590 lines
19 KiB
XML
590 lines
19 KiB
XML
<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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xml:id="sec-pkgs-dockerTools">
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<title>pkgs.dockerTools</title>
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<para>
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<varname>pkgs.dockerTools</varname> is a set of functions for creating and
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manipulating Docker images according to the
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<link xlink:href="https://github.com/moby/moby/blob/master/image/spec/v1.2.md#docker-image-specification-v120">
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Docker Image Specification v1.2.0 </link>. Docker itself is not used to
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perform any of the operations done by these functions.
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</para>
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<warning>
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<para>
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The <varname>dockerTools</varname> API is unstable and may be subject to
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backwards-incompatible changes in the future.
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</para>
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</warning>
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<section xml:id="ssec-pkgs-dockerTools-buildImage">
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<title>buildImage</title>
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<para>
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This function is analogous to the <command>docker build</command> command,
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in that it can be used to build a Docker-compatible repository tarball
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containing a single image with one or multiple layers. As such, the result
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is suitable for being loaded in Docker with <command>docker load</command>.
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</para>
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<para>
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The parameters of <varname>buildImage</varname> with relative example values
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are described below:
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</para>
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<example xml:id='ex-dockerTools-buildImage'>
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<title>Docker build</title>
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<programlisting>
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buildImage {
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name = "redis"; <co xml:id='ex-dockerTools-buildImage-1' />
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tag = "latest"; <co xml:id='ex-dockerTools-buildImage-2' />
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fromImage = someBaseImage; <co xml:id='ex-dockerTools-buildImage-3' />
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fromImageName = null; <co xml:id='ex-dockerTools-buildImage-4' />
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fromImageTag = "latest"; <co xml:id='ex-dockerTools-buildImage-5' />
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contents = pkgs.redis; <co xml:id='ex-dockerTools-buildImage-6' />
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runAsRoot = '' <co xml:id='ex-dockerTools-buildImage-runAsRoot' />
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#!${pkgs.runtimeShell}
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mkdir -p /data
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'';
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config = { <co xml:id='ex-dockerTools-buildImage-8' />
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Cmd = [ "/bin/redis-server" ];
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WorkingDir = "/data";
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Volumes = {
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"/data" = {};
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};
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};
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}
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</programlisting>
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</example>
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<para>
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The above example will build a Docker image <literal>redis/latest</literal>
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from the given base image. Loading and running this image in Docker results
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in <literal>redis-server</literal> being started automatically.
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</para>
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<calloutlist>
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<callout arearefs='ex-dockerTools-buildImage-1'>
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<para>
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<varname>name</varname> specifies the name of the resulting image. This is
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the only required argument for <varname>buildImage</varname>.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-buildImage-2'>
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<para>
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<varname>tag</varname> specifies the tag of the resulting image. By
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default it's <literal>null</literal>, which indicates that the nix output
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hash will be used as tag.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-buildImage-3'>
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<para>
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<varname>fromImage</varname> is the repository tarball containing the base
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image. It must be a valid Docker image, such as exported by
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<command>docker save</command>. By default it's <literal>null</literal>,
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which can be seen as equivalent to <literal>FROM scratch</literal> of a
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<filename>Dockerfile</filename>.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-buildImage-4'>
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<para>
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<varname>fromImageName</varname> can be used to further specify the base
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image within the repository, in case it contains multiple images. By
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default it's <literal>null</literal>, in which case
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<varname>buildImage</varname> will peek the first image available in the
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repository.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-buildImage-5'>
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<para>
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<varname>fromImageTag</varname> can be used to further specify the tag of
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the base image within the repository, in case an image contains multiple
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tags. By default it's <literal>null</literal>, in which case
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<varname>buildImage</varname> will peek the first tag available for the
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base image.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-buildImage-6'>
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<para>
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<varname>contents</varname> is a derivation that will be copied in the new
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layer of the resulting image. This can be similarly seen as <command>ADD
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contents/ /</command> in a <filename>Dockerfile</filename>. By default
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it's <literal>null</literal>.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-buildImage-runAsRoot'>
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<para>
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<varname>runAsRoot</varname> is a bash script that will run as root in an
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environment that overlays the existing layers of the base image with the
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new resulting layer, including the previously copied
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<varname>contents</varname> derivation. This can be similarly seen as
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<command>RUN ...</command> in a <filename>Dockerfile</filename>.
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<note>
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<para>
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Using this parameter requires the <literal>kvm</literal> device to be
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available.
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</para>
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</note>
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-buildImage-8'>
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<para>
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<varname>config</varname> is used to specify the configuration of the
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containers that will be started off the built image in Docker. The
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available options are listed in the
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<link xlink:href="https://github.com/moby/moby/blob/master/image/spec/v1.2.md#image-json-field-descriptions">
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Docker Image Specification v1.2.0 </link>.
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</para>
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</callout>
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</calloutlist>
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<para>
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After the new layer has been created, its closure (to which
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<varname>contents</varname>, <varname>config</varname> and
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<varname>runAsRoot</varname> contribute) will be copied in the layer itself.
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Only new dependencies that are not already in the existing layers will be
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copied.
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</para>
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<para>
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At the end of the process, only one new single layer will be produced and
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added to the resulting image.
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</para>
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<para>
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The resulting repository will only list the single image
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<varname>image/tag</varname>. In the case of
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<xref linkend='ex-dockerTools-buildImage'/> it would be
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<varname>redis/latest</varname>.
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</para>
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<para>
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It is possible to inspect the arguments with which an image was built using
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its <varname>buildArgs</varname> attribute.
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</para>
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<note>
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<para>
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If you see errors similar to <literal>getProtocolByName: does not exist (no
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such protocol name: tcp)</literal> you may need to add
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<literal>pkgs.iana-etc</literal> to <varname>contents</varname>.
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</para>
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</note>
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<note>
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<para>
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If you see errors similar to <literal>Error_Protocol ("certificate has
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unknown CA",True,UnknownCa)</literal> you may need to add
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<literal>pkgs.cacert</literal> to <varname>contents</varname>.
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</para>
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</note>
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<example xml:id="example-pkgs-dockerTools-buildImage-creation-date">
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<title>Impurely Defining a Docker Layer's Creation Date</title>
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<para>
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By default <function>buildImage</function> will use a static date of one
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second past the UNIX Epoch. This allows <function>buildImage</function> to
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produce binary reproducible images. When listing images with
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<command>docker images</command>, the newly created images will be listed
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like this:
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</para>
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<screen><![CDATA[
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$ docker images
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REPOSITORY TAG IMAGE ID CREATED SIZE
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hello latest 08c791c7846e 48 years ago 25.2MB
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]]></screen>
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<para>
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You can break binary reproducibility but have a sorted, meaningful
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<literal>CREATED</literal> column by setting <literal>created</literal> to
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<literal>now</literal>.
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</para>
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<programlisting><![CDATA[
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pkgs.dockerTools.buildImage {
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name = "hello";
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tag = "latest";
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created = "now";
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contents = pkgs.hello;
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config.Cmd = [ "/bin/hello" ];
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}
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]]></programlisting>
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<para>
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and now the Docker CLI will display a reasonable date and sort the images
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as expected:
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<screen><![CDATA[
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$ docker images
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REPOSITORY TAG IMAGE ID CREATED SIZE
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hello latest de2bf4786de6 About a minute ago 25.2MB
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]]></screen>
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however, the produced images will not be binary reproducible.
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</para>
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</example>
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</section>
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<section xml:id="ssec-pkgs-dockerTools-buildLayeredImage">
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<title>buildLayeredImage</title>
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<para>
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Create a Docker image with many of the store paths being on their own layer
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to improve sharing between images.
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</para>
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<variablelist>
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<varlistentry>
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<term>
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<varname>name</varname>
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</term>
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<listitem>
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<para>
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The name of the resulting image.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<varname>tag</varname> <emphasis>optional</emphasis>
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</term>
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<listitem>
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<para>
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Tag of the generated image.
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</para>
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<para>
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<emphasis>Default:</emphasis> the output path's hash
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<varname>contents</varname> <emphasis>optional</emphasis>
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</term>
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<listitem>
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<para>
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Top level paths in the container. Either a single derivation, or a list
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of derivations.
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</para>
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<para>
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<emphasis>Default:</emphasis> <literal>[]</literal>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<varname>config</varname> <emphasis>optional</emphasis>
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</term>
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<listitem>
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<para>
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Run-time configuration of the container. A full list of the options are
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available at in the
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<link xlink:href="https://github.com/moby/moby/blob/master/image/spec/v1.2.md#image-json-field-descriptions">
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Docker Image Specification v1.2.0 </link>.
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</para>
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<para>
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<emphasis>Default:</emphasis> <literal>{}</literal>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<varname>created</varname> <emphasis>optional</emphasis>
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</term>
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<listitem>
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<para>
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Date and time the layers were created. Follows the same
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<literal>now</literal> exception supported by
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<literal>buildImage</literal>.
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</para>
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<para>
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<emphasis>Default:</emphasis> <literal>1970-01-01T00:00:01Z</literal>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<varname>maxLayers</varname> <emphasis>optional</emphasis>
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</term>
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<listitem>
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<para>
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Maximum number of layers to create.
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</para>
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<para>
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<emphasis>Default:</emphasis> <literal>24</literal>
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<section xml:id="dockerTools-buildLayeredImage-arg-contents">
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<title>Behavior of <varname>contents</varname> in the final image</title>
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<para>
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Each path directly listed in <varname>contents</varname> will have a
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symlink in the root of the image.
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</para>
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<para>
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For example:
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<programlisting><![CDATA[
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pkgs.dockerTools.buildLayeredImage {
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name = "hello";
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contents = [ pkgs.hello ];
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}
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]]></programlisting>
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will create symlinks for all the paths in the <literal>hello</literal>
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package:
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<screen><![CDATA[
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/bin/hello -> /nix/store/h1zb1padqbbb7jicsvkmrym3r6snphxg-hello-2.10/bin/hello
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/share/info/hello.info -> /nix/store/h1zb1padqbbb7jicsvkmrym3r6snphxg-hello-2.10/share/info/hello.info
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/share/locale/bg/LC_MESSAGES/hello.mo -> /nix/store/h1zb1padqbbb7jicsvkmrym3r6snphxg-hello-2.10/share/locale/bg/LC_MESSAGES/hello.mo
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]]></screen>
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</para>
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</section>
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<section xml:id="dockerTools-buildLayeredImage-arg-config">
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<title>Automatic inclusion of <varname>config</varname> references</title>
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<para>
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The closure of <varname>config</varname> is automatically included in the
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closure of the final image.
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</para>
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<para>
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This allows you to make very simple Docker images with very little code.
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This container will start up and run <command>hello</command>:
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<programlisting><![CDATA[
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pkgs.dockerTools.buildLayeredImage {
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name = "hello";
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config.Cmd = [ "${pkgs.hello}/bin/hello" ];
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}
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]]></programlisting>
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</para>
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</section>
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<section xml:id="dockerTools-buildLayeredImage-arg-maxLayers">
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<title>Adjusting <varname>maxLayers</varname></title>
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<para>
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Increasing the <varname>maxLayers</varname> increases the number of layers
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which have a chance to be shared between different images.
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</para>
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<para>
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Modern Docker installations support up to 128 layers, however older
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versions support as few as 42.
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</para>
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<para>
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If the produced image will not be extended by other Docker builds, it is
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safe to set <varname>maxLayers</varname> to <literal>128</literal>. However
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it will be impossible to extend the image further.
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</para>
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<para>
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The first (<literal>maxLayers-2</literal>) most "popular" paths will have
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their own individual layers, then layer #<literal>maxLayers-1</literal>
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will contain all the remaining "unpopular" paths, and finally layer
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#<literal>maxLayers</literal> will contain the Image configuration.
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</para>
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<para>
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Docker's Layers are not inherently ordered, they are content-addressable
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and are not explicitly layered until they are composed in to an Image.
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</para>
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</section>
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</section>
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<section xml:id="ssec-pkgs-dockerTools-fetchFromRegistry">
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<title>pullImage</title>
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<para>
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This function is analogous to the <command>docker pull</command> command, in
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that it can be used to pull a Docker image from a Docker registry. By
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default <link xlink:href="https://hub.docker.com/">Docker Hub</link> is used
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to pull images.
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</para>
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<para>
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Its parameters are described in the example below:
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</para>
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<example xml:id='ex-dockerTools-pullImage'>
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<title>Docker pull</title>
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<programlisting>
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pullImage {
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imageName = "nixos/nix"; <co xml:id='ex-dockerTools-pullImage-1' />
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imageDigest = "sha256:20d9485b25ecfd89204e843a962c1bd70e9cc6858d65d7f5fadc340246e2116b"; <co xml:id='ex-dockerTools-pullImage-2' />
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finalImageName = "nix"; <co xml:id='ex-dockerTools-pullImage-3' />
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finalImageTag = "1.11"; <co xml:id='ex-dockerTools-pullImage-4' />
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sha256 = "0mqjy3zq2v6rrhizgb9nvhczl87lcfphq9601wcprdika2jz7qh8"; <co xml:id='ex-dockerTools-pullImage-5' />
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os = "linux"; <co xml:id='ex-dockerTools-pullImage-6' />
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arch = "x86_64"; <co xml:id='ex-dockerTools-pullImage-7' />
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}
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</programlisting>
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</example>
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<calloutlist>
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<callout arearefs='ex-dockerTools-pullImage-1'>
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<para>
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<varname>imageName</varname> specifies the name of the image to be
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downloaded, which can also include the registry namespace (e.g.
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<literal>nixos</literal>). This argument is required.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-pullImage-2'>
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<para>
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<varname>imageDigest</varname> specifies the digest of the image to be
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downloaded. This argument is required.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-pullImage-3'>
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<para>
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<varname>finalImageName</varname>, if specified, this is the name of the
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image to be created. Note it is never used to fetch the image since we
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prefer to rely on the immutable digest ID. By default it's equal to
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<varname>imageName</varname>.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-pullImage-4'>
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<para>
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<varname>finalImageTag</varname>, if specified, this is the tag of the
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image to be created. Note it is never used to fetch the image since we
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prefer to rely on the immutable digest ID. By default it's
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<literal>latest</literal>.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-pullImage-5'>
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<para>
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<varname>sha256</varname> is the checksum of the whole fetched image. This
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argument is required.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-pullImage-6'>
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<para>
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<varname>os</varname>, if specified, is the operating system of the
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fetched image. By default it's <literal>linux</literal>.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-pullImage-7'>
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<para>
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<varname>arch</varname>, if specified, is the cpu architecture of the
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fetched image. By default it's <literal>x86_64</literal>.
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</para>
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</callout>
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</calloutlist>
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<para>
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<literal>nix-prefetch-docker</literal> command can be used to get required
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image parameters:
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<screen>
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<prompt>$ </prompt>nix run nixpkgs.nix-prefetch-docker -c nix-prefetch-docker --image-name mysql --image-tag 5
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</screen>
|
|
|
|
Since a given <varname>imageName</varname> may transparently refer to a
|
|
manifest list of images which support multiple architectures and/or
|
|
operating systems, you can supply the <option>--os</option> and
|
|
<option>--arch</option> 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.
|
|
|
|
<screen>
|
|
<prompt>$ </prompt>nix-prefetch-docker --image-name mysql --image-tag 5 --arch x86_64 --os linux
|
|
</screen>
|
|
|
|
Desired image name and tag can be set using
|
|
<option>--final-image-name</option> and <option>--final-image-tag</option>
|
|
arguments:
|
|
|
|
<screen>
|
|
<prompt>$ </prompt>nix-prefetch-docker --image-name mysql --image-tag 5 --final-image-name eu.gcr.io/my-project/mysql --final-image-tag prod
|
|
</screen>
|
|
</para>
|
|
</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>
|