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<p class="MsoNormal">Team, I wanted to continue the discussion around Kustomize-based variable substitution from Monday’s SIG-YAML design call.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">There are two main Deckhand-like features we need out of Kustomize:  Layering and Substitution. 
<o:p></o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">Layering is something Kustomize does really well, via strategic merge. 
<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">Substitution is what's presenting some challenges, between custom plugins being unable to do late binding on variables (i.e., you only get one shot at a tree substitution using our
 VarReference plugin), and the fact that the Kustomize team is not really interested in enhancing variable capabilities overall.<o:p></o:p></li></ul>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">For one-shot-tree-substitution:  can we reframe the substitution problem as a layering problem?  If we:<o:p></o:p></p>
<ol style="margin-top:0in" start="1" type="1">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l1 level1 lfo2">Define variables+values in regular CRDs/Kustomize resources (rather than standalone transformer files)<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l1 level1 lfo2">Use normal Kustomize layering to override variable definitions an arbitrary number of times (e.g. function, composite, type levels)<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l1 level1 lfo2">Wait till layering is fully rendered before doing variable substitution<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l1 level1 lfo2">Avoid deploying these variable catalog CRDs to the cluster, via e.g. via an “airshipit.org/no-deploy” label<o:p></o:p></li></ol>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Then I think we would be able to accomplish multiple overrides for YAML tree variables, and recursive variable references, at the same time.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">#3 above then would require either a new plugin (Dmitry: does that sound possible?) or some kind of post-Kustomize step to fill in variables.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Am I missing anything?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Matt<o:p></o:p></p>
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