Elasticsearch Allow access from localhost and two other ips

I have an elasticsearch server setup at

http://hostname:9200. 

      

        
        
        
      

    

The server is bound to localhost in elasticsearch.yml as stated in https://www.digitalocean.com/community/tutorials/how-to-install-elasticsearch-on-an-ubuntu-vps . This only works so that localhost can connect to the server. I need to allow two other servers (worker nodes) to connect to the server to host data there. How can I bind additional ips so that elasticsearch server can be accessed from localhost and two other ips?