Prometheus metrics collection from tasks works in host networking mode, but not in bridged or 'virtual network' mode. This is because we derive the prometheus address from the task's port and 'localhost'. However in bridged and 'virtual network' mode, the task's port is not bound to localhost. It is bound to the local IP address instead. We should therefore scrape LOCAL_IP:PORT_NUMBER
Additionally, we should document that in 'virtual network' mode, the port must be mapped in order to enable prometheus metrics collection.
This need not block beta, but we must fix this by GA.