Question-101: Why do you want to enable the auto-starts of the few components in the Ambari?

Answer: If we enable the auto-start of a service or a component then it would not require manual effort to start a component. For example, you should enable the auto start for the worker nodes in the core Hadoop services, the DataNode, NameNode and YARN components in the HDFS. So what happen whenever these components are in the stopped status, then Ambari-agent will try to attempt the re-start of that component and does not require manual effort. Sometime you may want to disable this feature, because you don’t want to auto start the components which are in the stopped state.

Question-102: If I have removed one of the services using the Ambari from the Hadoop cluster, can I revert it?

Answer: No, its not doable. Once service is removed it can not be reversed, until and unless you re-install the same. And all the data related to that service will also be deleted.

Question-103: What happen to the data when you delete the DataNodes which are more than configured values against the property “dfs.replication.factor”?

Answer: Suppose you are deleting more Datanodes that the value which is configured in property “dfs.raplication.factor” without decommissioning at first will result in the Data loss permanently. (Think why, check HadoopExam training)

Question-104: If somebody has deleted the DataNode and you wanted to know who did this, how can you achive it?

Answer: As most of the services, applications have this feature in some way. Similarly, Ambari also manages the Audit logs and do the same things.

Question-105: Why by default OOZie UI (Get Oozie HandOn training access from HadoopExam)  is not installed on Apache Ambari?

Answer: Its because of Ext-JS GPL license, which is not included by default with the HDP2.6 and onwards. So to have Oozie UI available, you must include the Ext-JS installed on the Oozie server host and restart the Oozie service. During the restart operation, Ambari re-builds the Oozie war file and include the Ext-JS which you have installed in it and then Oozie UI would be available to you.