CouchDB is a NoSQL data store that stores data in the JSON format, similar to ElasticSearch. It can be queried with the map/reduce task and provides the REST API, so every operation can be done via HTTP API calls.
Using ElasticSearch to index and search CouchDB data is very handy, as it extends the CouchDB data store with Lucene's search capabilities.
You will need a working ElasticSearch cluster and a working CouchDB server to connect to.
In order to use the CouchDB river, perform the following steps:
First, you need to install the CouchDB river plugin, which is available on GitHub (https://github.com/elasticsearch/elasticsearch-river-couchdb), and is maintained by the ElasticSearch company. You can install the river plugin in the usual way:
bin/plugin -install elasticsearch/elasticsearch-river-couchdb/2.0.0