show "heartbeat lost" in Ambari web gui

I have 3 node in my cluster (namenode / datanode01 /datanode02) ,it’s normal after deploying
But yesterday i rebooted all hosts , datanode02 show “heartbeat lost ” in Ambari web gui .
#Ambari server : 1.7
#HDP 2.2
I check the ambari agent log ,it’s OK.
But the ambari server log ,like some wrong
………..
16:06:50,102 INFO [qtp2040340530-18] AbstractResourceProvider:614 – Received a updateService request, clusterName=Epistar_Hadoop, serviceName=OOZIE, request=clusterName=Epistar_Hadoop, serviceName=OOZIE, desiredState=INSTALLED
16:06:50,333 INFO [qtp2040340530-18] RoleCommandOrder:220 – Role command order info was loaded from file: /var/lib/ambari-server/resources/stacks/HDP/2.2/role_command_order.json
16:07:00,130 WARN [qtp1063066389-85] HeartBeatHandler:411 – Operation failed – may be retried. Service component host: DATANODE, host: datanode02.epistar.com.tw Action id63-1
16:07:00,301 WARN [qtp1063066389-80] HeartBeatHandler:411 – Operation failed – may be retried. Service component host: APP_TIMELINE_SERVER, host: namenode.epistar.com.tw Action id63-1
16:07:00,972 WARN [Thread-20] ActionScheduler:275 – Operation completely failed, aborting request id:63
………..