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dockerTools.buildImage: support impure dates #47005

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merged 1 commit into from Sep 20, 2018
Merged

dockerTools.buildImage: support impure dates #47005

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39 changes: 39 additions & 0 deletions doc/functions.xml
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Expand Up @@ -638,6 +638,45 @@ buildImage {
<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>
Because dates are an impurity, by default
<function>buildImage</function> will use a static date of one
second past the UNIX Epoch. This can be a bit frustrating when
listing docker images in the CLI:
</para>
<screen><![CDATA[
$ docker image list
REPOSITORY TAG IMAGE ID CREATED SIZE
hello latest 08c791c7846e 48 years ago 25.2MB
]]></screen>
<para>
If you want to trade the purity for a better user experience,
you can set <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:
</para>
<screen><![CDATA[
$ docker image list
REPOSITORY TAG IMAGE ID CREATED SIZE
hello latest de2bf4786de6 About a minute ago 25.2MB
]]></screen>
</example>
</section>

<section xml:id="ssec-pkgs-dockerTools-fetchFromRegistry">
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19 changes: 13 additions & 6 deletions pkgs/build-support/docker/default.nix
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Expand Up @@ -450,11 +450,18 @@ rec {
baseName = baseNameOf name;

# Create a JSON blob of the configuration. Set the date to unix zero.
baseJson = writeText "${baseName}-config.json" (builtins.toJSON {
inherit created config;
architecture = "amd64";
os = "linux";
});
baseJson = let
pure = writeText "${baseName}-config.json" (builtins.toJSON {
inherit created config;
architecture = "amd64";
os = "linux";
});
impure = runCommand "${baseName}-config.json"
{ buildInputs = [ jq ]; }
''
jq ".created = \"$(TZ=utc date --iso-8601="seconds")\"" ${pure} > $out
'';
in if created == "now" then impure else pure;
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there was some question about why not just use builtins.currentTime.

builtins.currentTime will never be a cache hit, whereas this method will cache while still achieving the intended effect.


layer =
if runAsRoot == null
Expand Down Expand Up @@ -577,7 +584,7 @@ rec {
currentID=$layerID
while [[ -n "$currentID" ]]; do
layerChecksum=$(sha256sum image/$currentID/layer.tar | cut -d ' ' -f1)
imageJson=$(echo "$imageJson" | jq ".history |= [{\"created\": \"${created}\"}] + .")
imageJson=$(echo "$imageJson" | jq ".history |= [{\"created\": \"$(jq -r .created ${baseJson})\"}] + .")
imageJson=$(echo "$imageJson" | jq ".rootfs.diff_ids |= [\"sha256:$layerChecksum\"] + .")
manifestJson=$(echo "$manifestJson" | jq ".[0].Layers |= [\"$currentID/layer.tar\"] + .")

Expand Down