By default, Elasticsearch will listen to the public interfaces (`_site_` cf. https://www.elastic.co/guide/en/elasticsearch/reference/5.0/important-settings.html#network.host), so you will have to secure it, with firewall rules for example.
*`elasticsearch_plugin_head` : enable the plugin installation (default: `False`) ;
*`elasticsearch_plugin_head_basedir`: base directory (default : `/var/www`) ;
*`elasticsearch_plugin_head_clone_name`: directory name for git clone.
To use this plugin, you have to run the built-in webserver (using Grunt/NodeJS), or point a webserver to the path. More details here : https://github.com/mobz/elasticsearch-head#running-with-built-in-server
For example, to run the built-in server, with "www-data" user :