Below you will find details on various compatibility issues and quirks that you may be effected by in your environment.
When Google configure the control plane for private clusters, they automatically configure VPC peering between your Kubernetes cluster's network and a separate Google managed project.
In order to restrict what Google are able to access within your cluster, the
firewall rules configured restrict access to your Kubernetes pods. This will
mean that you will experience the webhook to not work and experience errors such
Internal error occurred: failed calling admission webhook ... the server is currently unable to handle the request.
In order to use the webhook component with a GKE private cluster, you must configure an additional firewall rule to allow the GKE control plane access to your webhook pod.
You can read more information on how to add firewall rules for the GKE control plane nodes in the GKE docs.
Disabling the webhook is not supported anymore since