The YARN REST API can report on the following properties:
allocatedMB: The sum of memory in MB allocated to the application's running containers
allocatedVCores: The sum of virtual cores allocated to the application's running containers
runningContainers: The number of containers currently running for the application
Currently, the RM Web UI does not report on these items (at least I couldn't find any entries within the Web UI).
It would be useful for YARN Application and Resource troubleshooting to have these properties and their corresponding values exposed on the RM WebUI.