I'\m being ruthless here and saying -1 until we have resolved
YARN-3539; that is the REST API of V1 is actually written down in the documents with a statement of that it is one of the stable REST APIs.
Once that is done, new aspects of the REST API can be added, with updates to the documentation.
If you look at that patch, it already documents the fact that a GET of ws/v1/timeline/ actually returns the about details, though as the Java structure representing this, org.apache.hadoop.yarn.server.timeline.webapp.TimelineWebServices is hidden in the implementation classes. It MUST be in the YARN API JAR. Moving it in to hadoop-yarn-server-applicationhistoryservice is not sufficient, as it is still unusable by external callers who do not have the server JAR on their classpath.
Finally,the assertNotNull() assertions need to have diagnostics strings, simply the name of the null field would be enough. Otherwise it's not easy trying to track down a regression