I've created an vpc internal http load balancer - using GCP's new Traffic Director, consisting of a forwarding rule, url map, couple backends pointing to VMs and NEGs. The solution works fine (end to end) - however none of the specific loadbalancer metrics from stackdriver show up for the above mentioned objects (under https://cloud.google.com/monitoring/api/metrics_gcp#gcp-loadbalancing).
Checked for any alpha metrics, no luck. Essentially the objects created are part of same abstraction google has for load balancers, but no metrics are collected. Since Traffic Director is essentially istio, I looked also on how to get istio metrics, seems the only way to get any metrics is via https://cloud.google.com/istio/docs/istio-on-gke/overview - which is odd because I can use traffic director only with VMs.
I expected to have some observability on the traffic director created internal load balancers but there is none.