A new server has been added to yarn. It is a web proxy that sits in front of the AM web UI. The server is controlled by the yarn.web-proxy.address config. If that config is set, and it points to an address that is different then the RM web interface then a separate proxy server needs to be launched.
This can be done by running
yarn-daemon.sh start proxyserver
If a separate proxy server is needed other configs also may need to be set, if security is enabled.
The proxy server is stateless and should be able to support a VIP or other load balancing sitting in front of multiple instances of this server.