managed-by is set at install time by the managing installer, and should not be templated.

[bleggett]

app.kubernetes.io/managed-by: Helm is automatically applied to resources installed by Helm via helm install, and does not need to be (read: should not be) manually templated. The label is an install-time label that should be applied by the tool actually installing the resources into the cluster.

This matters because helm template should (and by default will) produce YAML without this label, as it is unknown at template-time what will "manage" the resource - e.g. helm template | kubectl apply -f - should not produce resources with the app.kubernetes.io/managed-by: Helm label, because the resources are not managed by helm.

xref: istio/istio#53698

and: #3389