Agreed and I understand the use of $ZK_HOST inside Morphlines File.

Earlier what I was missing was what value should I use for the morphlineFile property in flume configuration (becuase I am specifying the morphline configuration in the Morphlines File property under Flume-NG Solr Sink), but re-reading the "Using Flume with Search" pointed me in the right direction -- I had to use morphlines.conf as the value for the morphlineFile property

Thanks for your help