Enhancing Proxy Host and Port Resolution Logging in WebAppUtils

The method getProxyHostsAndPortsForAmFilter is designed to retrieve proxy hosts and ports for the Application Master (AM) filter based on the YARN configuration. If the yarn.web-proxy.address parameter is not set or is empty, the method attempts to resolve the addresses using ResourceManager (RM) High Availability (HA) addresses or falls back to the RM WebApp URL without the scheme. The current implementation does not provide detailed logging, making it difficult to diagnose issues related to proxy address resolution, especially when the fallback mechanisms are triggered.
 
Expected Behavior:
The system should log information and warnings when the proxy address is not set or is empty, providing insight into the resolution process, including when it falls back to RM HA addresses or the RM WebApp URL. This logging would assist users in ensuring correct proxy configuration and identifying potential issues during address resolution.
 
How-to-Fix:
We propose adding log statements that will expose the resolution process of proxy addresses, including the fallback mechanisms when the yarn.web-proxy.address parameter is not set or is empty.