How to check if Elasticsearch is running using REST API ?

Check the IP address and port where ES is running on the server :

# vi /etc/elasticsearch/elasticsearch.yml

http.port: 9200

network.host: 10.170.208.44

AT CLIENT SIDE

Check the URL with IP and port of ES in the browser :

http://10.170.208.44:9200/

AT SEVER SIDE

Use curl command 

# curl -XGET 'http://localhost:9200/'