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<nav id="TableOfContents">
<ul>
<li><a href="#specification-in-kustomizationyaml">Specification in <code>kustomization.yaml</code></a></li>
<li><a href="#configuration">Configuration</a></li>
<li><a href="#placement">Placement</a></li>
<li><a href="#execution">Execution</a>
<ul>
<li></li>
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<a href="https://kubernetes-sigs.github.io/kustomize/guides/plugins/">Kustomize Plugins</a>
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<h1>Kustomize Plugins</h1>
<div class="lead">Kustomize plugins guide</div>
<p>Kustomize offers a plugin framework allowing people to write their own resource <em>generators</em>
and <em>transformers</em>.</p>
<p>Write a plugin when changing <a href="https://github.com/kubernetes-sigs/kustomize/tree/master/examples/generatorOptions.md">generator options</a>
or <a href="https://github.com/kubernetes-sigs/kustomize/tree/master/examples/transformerconfigs">transformer configs</a> doesn&rsquo;t meet your needs.</p>
<ul>
<li>
<p>A <em>generator</em> plugin could be a helm chart
inflator, or a plugin that emits all the
components (deployment, service, scaler,
ingress, etc.) needed by someone&rsquo;s <a href="https://12factor.net">12-factor</a>
application, based on a smaller number of free
variables.</p>
</li>
<li>
<p>A <em>transformer</em> plugin might perform special
container command line edits, or any other
transformation beyond those provided by the
builtin (<code>namePrefix</code>, <code>commonLabels</code>, etc.)
transformers.</p>
</li>
</ul>
<h2 id="specification-in-kustomizationyaml">Specification in <code>kustomization.yaml</code></h2>
<p>Start by adding a <code>generators</code> and/or <code>transformers</code>
field to your kustomization.</p>
<p>Each field accepts a string list:</p>
<blockquote>
<pre><code>generators:
- relative/path/to/some/file.yaml
- relative/path/to/some/kustomization
- /absolute/path/to/some/kustomization
- https://github.com/org/repo/some/kustomization
transformers:
- {as above}
</code></pre></blockquote>
<p>The value of each entry in a <code>generators</code> or
<code>transformers</code> list must be a relative path to a
YAML file, or a path or URL to a <a href="/kustomize/api-reference/glossary#kustomization">kustomization</a>.
This is the same format as demanded by the
<code>resources</code> field.</p>
<p>YAML files are read from disk directly. Paths or
URLs leading to kustomizations trigger an
in-process kustomization run. Each of the
resulting objects is now further interpreted by
kustomize as a <em>plugin configuration</em> object.</p>
<h2 id="configuration">Configuration</h2>
<p>A kustomization file could have the following lines:</p>
<pre><code>generators:
- chartInflator.yaml
</code></pre><p>Given this, the kustomization process would expect
to find a file called <code>chartInflator.yaml</code> in the
kustomization <a href="/kustomize/api-reference/glossary#kustomization-root">root</a>.</p>
<p>This is the plugin&rsquo;s configuration file;
it contains a YAML configuration object.</p>
<p>The file <code>chartInflator.yaml</code> could contain:</p>
<pre><code>apiVersion: someteam.example.com/v1
kind: ChartInflator
metadata:
name: notImportantHere
chartName: minecraft
</code></pre><p><strong>The <code>apiVersion</code> and <code>kind</code> fields are
used to locate the plugin.</strong></p>
<p>Thus, these fields are required. They are also
required because a kustomize plugin configuration
object is also a <a href="/kustomize/api-reference/glossary#kubernetes-style-object">k8s object</a>.</p>
<p>To get the plugin ready to generate or transform,
it is given the entire contents of the
configuration file.</p>
<p>For more examples of plugin configuration YAML,
browse the unit tests below the <a href="https://github.com/kubernetes-sigs/kustomize/tree/master/plugin/builtin">plugins</a> root,
e.g. the tests for <a href="https://github.com/kubernetes-sigs/kustomize/tree/master/plugin/someteam.example.com/v1/chartinflator/ChartInflator_test.go">ChartInflator</a> or
<a href="https://github.com/kubernetes-sigs/kustomize/tree/master/plugin/builtin/prefixsuffixtransformer/PrefixSuffixTransformer_test.go">NameTransformer</a>.</p>
<h2 id="placement">Placement</h2>
<p>Each plugin gets its own dedicated directory named</p>
<pre><code>$XDG_CONFIG_HOME/kustomize/plugin
/${apiVersion}/LOWERCASE(${kind})
</code></pre><p>The default value of <a href="https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html"><code>XDG_CONFIG_HOME</code></a> is
<code>$HOME/.config</code>.</p>
<p>The one-plugin-per-directory requirement eases
creation of a plugin bundle (source, tests, plugin
data files, etc.) for sharing.</p>
<p>In the case of a <a href="#go-plugins">Go plugin</a>, it also
allows one to provide a <code>go.mod</code> file for the
single plugin, easing resolution of package
version dependency skew.</p>
<p>When loading, kustomize will first look for an
<em>executable</em> file called</p>
<pre><code>$XDG_CONFIG_HOME/kustomize/plugin
/${apiVersion}/LOWERCASE(${kind})/${kind}
</code></pre><p>If this file is not found or is not executable,
kustomize will look for a file called <code>${kind}.so</code>
in the same directory and attempt to load it as a
<a href="#go-plugins">Go plugin</a>.</p>
<p>If both checks fail, the plugin load fails the overall
<code>kustomize build</code>.</p>
<h2 id="execution">Execution</h2>
<p>Plugins are only used during a run of the
<code>kustomize build</code> command.</p>
<p>Generator plugins are run after processing the
<code>resources</code> field (which itself can be viewed as a
generator, simply reading objects from disk).</p>
<p>The full set of resources is then passed into the
transformation pipeline, wherein builtin
transformations like <code>namePrefix</code> and
<code>commonLabel</code> are applied (if they were specified
in the kustomization file), followed by the
user-specified transformers in the <code>transformers</code>
field.</p>
<p>The order specified in the <code>transformers</code> field is
respected, as transformers cannot be expected to
be commutative.</p>
<h4 id="no-security">No Security</h4>
<p>Kustomize plugins do not run in any kind of
kustomize-provided sandbox. There&rsquo;s no notion
of <em>&ldquo;plugin security&rdquo;</em>.</p>
<p>A <code>kustomize build</code> that tries to use plugins but
omits the flag</p>
<blockquote>
<p><code>--enable_alpha_plugins</code></p>
</blockquote>
<p>will not load plugins and will fail with a
warning about plugin use.</p>
<p>The use of this flag is an opt-in acknowledging
the unstable (alpha) plugin API, the absence of
plugin provenance, and the fact that a plugin
is not part of kustomize.</p>
<p>To be clear, some kustomize plugin downloaded
from the internet might wonderfully transform
k8s config in a desired manner, while also
quietly doing anything the user could do to the
system running <code>kustomize build</code>.</p>
<h2 id="authoring">Authoring</h2>
<p>There are two kinds of plugins, <a href="#exec-plugins">exec</a> and <a href="#go-plugins">Go</a>.</p>
<h3 id="exec-plugins">Exec plugins</h3>
<p>A <em>exec plugin</em> is any executable that accepts a
single argument on its command line - the name of
a YAML file containing its configuration (the file name
provided in the kustomization file).</p>
<blockquote>
<p>TODO: restrictions on plugin to allow the <em>same exec
plugin</em> to be targeted by both the
<code>generators</code> and <code>transformers</code> fields.</p>
<ul>
<li>first arg could be the fixed string
<code>generate</code> or <code>transform</code>,
(the name of the configuration file moves to
the 2nd arg), or</li>
<li>or by default an exec plugin behaves as a tranformer
unless a flag <code>-g</code> is provided, switching the
exec plugin to behave as a generator.</li>
</ul>
</blockquote>
<h4 id="examples">Examples</h4>
<ul>
<li><a href="https://github.com/kubernetes-sigs/kustomize/tree/master/plugin/someteam.example.com/v1/chartinflator">helm chart inflator</a> - A generator that inflates a helm chart.</li>
<li><a href="https://github.com/kubernetes-sigs/kustomize/tree/master/plugin/someteam.example.com/v1/bashedconfigmap">bashed config map</a> - Super simple configMap generation from bash.</li>
<li><a href="https://github.com/kubernetes-sigs/kustomize/tree/master/plugin/someteam.example.com/v1/sedtransformer">sed transformer</a> - Define your unstructured edits using a
plugin like this one.</li>
<li><a href="https://github.com/kubernetes-sigs/kustomize/tree/master/plugin/someteam.example.com/v1/gogetter">hashicorp go-getter</a> - Download kustomize layes and build it to generate resources</li>
</ul>
<p>A generator plugin accepts nothing on <code>stdin</code>, but emits
generated resources to <code>stdout</code>.</p>
<p>A transformer plugin accepts resource YAML on <code>stdin</code>,
and emits those resources, presumably transformed, to
<code>stdout</code>.</p>
<p>kustomize uses an exec plugin adapter to provide
marshalled resources on <code>stdin</code> and capture
<code>stdout</code> for further processing.</p>
<h4 id="generator-options">Generator Options</h4>
<p>A generator exec plugin can adjust the generator options for the resources it emits by setting one of the following internal annotations.</p>
<blockquote>
<p>NOTE: These annotations are local to kustomize and will not be included in the final output.</p>
</blockquote>
<p><strong><code>kustomize.config.k8s.io/needs-hash</code></strong></p>
<p>Resources can be marked as needing to be processed by the internal hash transformer by including the <code>needs-hash</code> annotation. When set valid values for the annotation are <code>&quot;true&quot;</code> and <code>&quot;false&quot;</code> which respectively enable or disable hash suffixing for the resource. Omitting the annotation is equivalent to setting the value <code>&quot;false&quot;</code>.</p>
<p>If this annotation is set on a resource not supported by the hash transformer the build will fail.</p>
<p>Example:</p>
<div class="highlight"><pre style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-yaml" data-lang="yaml"><span style="color:#204a87;font-weight:bold">apiVersion</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline"> </span>v1<span style="color:#f8f8f8;text-decoration:underline">
</span><span style="color:#f8f8f8;text-decoration:underline"></span><span style="color:#204a87;font-weight:bold">kind</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline"> </span>ConfigMap<span style="color:#f8f8f8;text-decoration:underline">
</span><span style="color:#f8f8f8;text-decoration:underline"></span><span style="color:#204a87;font-weight:bold">metadata</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline">
</span><span style="color:#f8f8f8;text-decoration:underline"> </span><span style="color:#204a87;font-weight:bold">name</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline"> </span>cm-test<span style="color:#f8f8f8;text-decoration:underline">
</span><span style="color:#f8f8f8;text-decoration:underline"> </span><span style="color:#204a87;font-weight:bold">annotations</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline">
</span><span style="color:#f8f8f8;text-decoration:underline"> </span><span style="color:#204a87;font-weight:bold">kustomize.config.k8s.io/needs-hash</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline"> </span><span style="color:#4e9a06">&#34;true&#34;</span><span style="color:#f8f8f8;text-decoration:underline">
</span><span style="color:#f8f8f8;text-decoration:underline"></span><span style="color:#204a87;font-weight:bold">data</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline">
</span><span style="color:#f8f8f8;text-decoration:underline"> </span><span style="color:#204a87;font-weight:bold">foo</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline"> </span>bar<span style="color:#f8f8f8;text-decoration:underline">
</span></code></pre></div><p><strong><code>kustomize.config.k8s.io/behavior</code></strong></p>
<p>The <code>behavior</code> annotation will influence how conflicts are handled for resources emitted by the plugin. Valid values include &ldquo;create&rdquo;, &ldquo;merge&rdquo;, and &ldquo;replace&rdquo; with &ldquo;create&rdquo; being the default.</p>
<p>Example:</p>
<div class="highlight"><pre style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-yaml" data-lang="yaml"><span style="color:#204a87;font-weight:bold">apiVersion</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline"> </span>v1<span style="color:#f8f8f8;text-decoration:underline">
</span><span style="color:#f8f8f8;text-decoration:underline"></span><span style="color:#204a87;font-weight:bold">kind</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline"> </span>ConfigMap<span style="color:#f8f8f8;text-decoration:underline">
</span><span style="color:#f8f8f8;text-decoration:underline"></span><span style="color:#204a87;font-weight:bold">metadata</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline">
</span><span style="color:#f8f8f8;text-decoration:underline"> </span><span style="color:#204a87;font-weight:bold">name</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline"> </span>cm-test<span style="color:#f8f8f8;text-decoration:underline">
</span><span style="color:#f8f8f8;text-decoration:underline"> </span><span style="color:#204a87;font-weight:bold">annotations</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline">
</span><span style="color:#f8f8f8;text-decoration:underline"> </span><span style="color:#204a87;font-weight:bold">kustomize.config.k8s.io/behavior</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline"> </span><span style="color:#4e9a06">&#34;merge&#34;</span><span style="color:#f8f8f8;text-decoration:underline">
</span><span style="color:#f8f8f8;text-decoration:underline"></span><span style="color:#204a87;font-weight:bold">data</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline">
</span><span style="color:#f8f8f8;text-decoration:underline"> </span><span style="color:#204a87;font-weight:bold">foo</span><span style="color:#000;font-weight:bold">:</span><span style="color:#f8f8f8;text-decoration:underline"> </span>bar<span style="color:#f8f8f8;text-decoration:underline">
</span></code></pre></div><h3 id="go-plugins">Go plugins</h3>
<p>Be sure to read <a href="goPluginCaveats.md">Go plugin caveats</a>.</p>
<p>A <code>.go</code> file can be a <a href="https://golang.org/pkg/plugin/">Go plugin</a> if it declares
&lsquo;main&rsquo; as it&rsquo;s package, and exports a symbol to
which useful functions are attached.</p>
<p>It can further be used as a <em>kustomize</em> plugin if
the symbol is named &lsquo;KustomizePlugin&rsquo; and the
attached functions implement the <code>Configurable</code>,
<code>Generator</code> and <code>Transformer</code> interfaces.</p>
<p>A Go plugin for kustomize looks like this:</p>
<blockquote>
<pre><code>package main
import (
&quot;sigs.k8s.io/kustomize/api/ifc&quot;
&quot;sigs.k8s.io/kustomize/api/resmap&quot;
...
)
type plugin struct {...}
var KustomizePlugin plugin
func (p *plugin) Config(
ldr ifc.Loader,
rf *resmap.Factory,
c []byte) error {...}
func (p *plugin) Generate() (resmap.ResMap, error) {...}
func (p *plugin) Transform(m resmap.ResMap) error {...}
</code></pre></blockquote>
<p>Use of the identifiers <code>plugin</code>, <code>KustomizePlugin</code>
and implementation of the method signature
<code>Config</code> is required.</p>
<p>Implementing the <code>Generator</code> or <code>Transformer</code>
method allows (respectively) the plugin&rsquo;s config
file to be added to the <code>generators</code> or
<code>transformers</code> field in the kustomization file.
Do one or the other or both as desired.</p>
<h4 id="examples-1">Examples</h4>
<ul>
<li><a href="https://github.com/kubernetes-sigs/kustomize/tree/master/plugin/someteam.example.com/v1/someservicegenerator">service generator</a> - generate a service from a name and port argument.</li>
<li><a href="https://github.com/kubernetes-sigs/kustomize/tree/master/plugin/someteam.example.com/v1/stringprefixer">string prefixer</a> - uses the value in <code>metadata/name</code> as the prefix.
This particular example exists to show how a plugin can
transform the behavior of a plugin. See the
<code>TestTransformedTransformers</code> test in the <code>target</code> package.</li>
<li><a href="https://github.com/kubernetes-sigs/kustomize/tree/master/plugin/someteam.example.com/v1/dateprefixer">date prefixer</a> - prefix the current date to resource names, a simple
example used to modify the string prefixer plugin just mentioned.</li>
<li><a href="https://github.com/kubernetes-sigs/kustomize/tree/master/plugin/someteam.example.com/v1/secretsfromdatabase">secret generator</a> - generate secrets from a toy database.</li>
<li><a href="https://github.com/monopole/sopsencodedsecrets">sops encoded secrets</a> - a more complex secret generator.</li>
<li><a href="https://github.com/kubernetes-sigs/kustomize/tree/master/plugin/builtin">All the builtin plugins</a>.
User authored plugins are
on the same footing as builtin operations.</li>
</ul>
<p>A Go plugin can be both a generator and a
transformer. The <code>Generate</code> method will run along
with all the other generators before the
<code>Transform</code> method runs.</p>
<p>Here&rsquo;s a build command that sensibly assumes the
plugin source code sits in the directory where
kustomize expects to find <code>.so</code> files:</p>
<pre><code>d=$XDG_CONFIG_HOME/kustomize/plugin\
/${apiVersion}/LOWERCASE(${kind})
go build -buildmode plugin \
-o $d/${kind}.so $d/${kind}.go
</code></pre>
<div class="section-index">
<hr class="panel-line">
<div class="entry">
<h5>
<a href="/kustomize/guides/plugins/builtins/">Builtin Plugins</a>
</h5>
<p>Builtin Plugins</p>
</div>
<div class="entry">
<h5>
<a href="/kustomize/guides/plugins/execpluginguidedexample/">Exec plugin on linux</a>
</h5>
<p>Exec plugin on linux in 60 seconds</p>
</div>
<div class="entry">
<h5>
<a href="/kustomize/guides/plugins/goplugincaveats/">Go plugin Caveats</a>
</h5>
<p>Go plugin Caveats</p>
</div>
<div class="entry">
<h5>
<a href="/kustomize/guides/plugins/gopluginguidedexample/">Go plugin example</a>
</h5>
<p>Go plugin example</p>
</div>
</div>
<div class="text-muted mt-5 pt-3 border-top">Last modified June 7, 2020: <a href="https://github.com/kubernetes-sigs/kustomize/commit/a2ea87d167bfd7a9dce16ff47d93b379f2a2d80d">Convert docs to docsy (a2ea87d1)</a>
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