The Google Compute Engine (GCE) Cloud plugin allows to use GCE API for the unicast discovery mechanism.
'org.elasticsearch.plugin:cloud-gce:2.1.0'
<dependency>
<groupId>org.elasticsearch.plugin</groupId>
<artifactId>cloud-gce</artifactId>
<version>2.1.0</version>
</dependency>
<dependency org="org.elasticsearch.plugin" name="cloud-gce" rev="2.1.0"/>
"org.elasticsearch.plugin", "cloud-gce", "2.1.0"