What functionality becomes unavailable when App Timeline Server isn't running?
I know Ambari Tez View becomes unavailable (showing an error that indicates it is impossible to connect with ATS) when ATS isn't running.
Of course, ATS WebUI becomes unavailable.
But, as far as I saw, ResourceManager runs as usual and yarn cli like "yarn application -status" also runs as usual.
As for Spark application, it looks no damage.
Spark History Server WebUI shows as usual because Spark History Server only depends on HDFS.
Is there any other problem?