Support for ElasticSearch 5.0+ Version

[atulagrawal]

Site plugins are not supported after 5.0 version and structure for plugins have also changed.

Please refer below link for references:
https://www.elastic.co/guide/en/elasticsearch/reference/5.0/breaking_50_plugins.html#_site_plugins_removed

If you install the plugin, you get following error:
ERROR: elasticsearch directory is missing in the plugin zip

[derickson]

Duplicate of:
#571

Rivers have been removed from Elasticsearch

[tchcxp]

@atulagrawal River is no longer supported by ES.

[ZhongLIFR]

What a pity! we cannot use elasticsearch-river-mongodb for elasticsearch 6.0+ version