what are the tools which we can use for automatic alerts/notification.
You can use Ambari EMail Notification or SNMP Notification feature. Please see: https://docs.hortonworks.com/HDPDocuments/Ambari-184.108.40.206/bk_ambari-user-guide/content/configuring_no...
Example: (Email) Setting Gmail based Alert Via Ambari: https://community.hortonworks.com/articles/40361/how-to-troubleshoot-ambari-alerts-notification.html
SNMP Notification with Ambari : https://community.hortonworks.com/articles/74370/snmp-alert.html
Also ambari provides an option to the user to create their own custom alerts. So based on your requirement you can have your own alerts registered.