Issue when indexing to elasticsearch from apache nutch
From further research I got the solution. The error is coming up because of the version mismatch in indexer plugin of nutch (which was ES 1.4.1).
One solution to this is to download the source from https://github.com/apache/nutch/blob/master/ and then customize the plugin version with your elastic server version by following these instructions given in src/plugin/indexer-elastic/howto_upgrade_es.txt.
Upgrade elasticsearch dependency in src/plugin/indexer-elastic/ivy.xml
Upgrade the Elasticsearch specific dependencies in src/plugin/indexer-elastic/plugin.xml To get the list of dependencies and their versions execute: $ ant -f ./build-ivy.xml
$ ls lib/Build from nutch source folder using ant or any other build tool.
Then we can index to ElasticSearch without this issue. Cheers :)