Recently I setup email notifications in Ambari (18.104.22.168) to receive notifications when alert states change. I've found that throughout each day the YARN alert App Timeline Web UI: Connection Failed switches from CRITICAL (connection timed out on port 8188) to OK. This happens 12 / 14 times a day. I'm unsure why this is? I have a basic 2 node cluster, the App Timeline and History Server components are on node 1, and the Resource Manager is on node 1 if that helps.
Any thoughts on why this might happen - it doesn't seem to effect performance.