YARN-3030, to start the per-app aggregator only for a started AM container, we need to determine if the container is an AM container or not from the context in NM (we can do it on RM). This information is missing, such that we worked around to considered the container with ID "xxxx_01" as the AM container. Unfortunately, this is neither necessary or sufficient condition. We need to have a way to determine if a container is an AM container on NM. We can add flag to the container object or create an API to do the judgement. Perhaps the distributed AM information may also be useful to YARN-2877.