Currently webhoook admission plugin doesn't have a dialer: https://github.com/kubernetes/kubernetes/blob/master/plugin/pkg/admission/webhook/admission.go#L260

Probably we need to plumb the dialer to the client like aggregator does: https://github.com/kubernetes/kubernetes/blob/master/staging/src/k8s.io/kube-aggregator/pkg/apiserver/handler_proxy.go#L213. Otherwise the plugin won't be able to work in gke.

cc @mandarjog @cheftako