copy the public key of the ambari host to the node you are adding in the .ssh/authorized_keys and also vice versa to allow the password less authentication between the two hosts and then try register the host again. ... View more

You have a "hoststate" and/or "hosts" table in ambari database which might have an entry of that hostsname which will give you that WARN [ambari-hearbeat-monitor] HeartbeatMonitor:154 - Heartbeat lost from host hostname" on every ambari-server restart is performed as it checks those tables. You might want to have a check if the entry exists then remove those entries by stopping the ambari-server and stopping the ambari-agent of those host which gives you that warning. Because if the ambari-agent is in running state then you will see the same issue again. ... View more