efaultValue: &lt;VALUE&gt;      # optional
</code></pre><div><aside class="callout warning"><div class=type><svg class="large-icon"><use xlink:href="/v1.8/img/icons.svg#callout-warning"/></svg></div><div class=content>In order to add custom tags based on environmental variables, you must
modify the <code>istio-sidecar-injector</code> ConfigMap in your root Istio system namespace.</div></aside></div></li><li><p>Client request header option can be used to populate tag value from an
incoming client request hea