For evaluation purpose, I am planning to install everything on the same host machine. Do I have to install Ambari-Agent also before I can add the host machine as a node in the cluster ??
Yes, install both server and agent on same node. Be careful with trying to do too many components/services on a single node with small ram/cores. If you try to run/install all of them you will have troubles getting cluster stable. Minimal install is like Hdfs, Yarn, MapReduce, AmbariMetrics, Zookeeper, Hive/Tez, Ranger.
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Steven @ DFHZ