Several tasks will be achieved in this JIRA based on the demo patch in MAPREDUCE-6608:
1. AM discovery base on YARN register service. Could be replaced by YARN-4758 later due to scale up issue.
2. Retry logic for TaskUmbilicalProtocol RPC connection
3. In-flight task recover after AM restart via JHS
4. Configuration to control the behavior compatible with previous when not enable this feature (by default).
All security related issues and other concerns discussed in MAPREDUCE-6608 will be addressed in follow up JIRAs.