Major Description
Hadoop has a few services with HA setups and it is common to set them behind Load Balancers.
We should add a way for the Load Balancers to understand what should be the UI to show.
For example, the standby RM just redirects the requests to the active RM.
However, if both RMs are behind a Load Balancer the IP might not be reachable.
Most Load balancers have probes to check if a server reports HTTP code 200:
Components in Hadoop (e.g., NN, RM, Router,...) should have a unified way to report if they are active.