Install the index-elasticsearch.jar into the $GERRIT_SITE/lib
directory.
Add the index-elasticsearch module to $GERRIT_SITE/etc/gerrit.config
as follows:
[gerrit] installIndexModule = com.google.gerrit.elasticsearch.ElasticIndexModule
When installing the module on Gerrit replicas, use following example:
[gerrit] installIndexModule = com.google.gerrit.elasticsearch.ReplicaElasticIndexModule
For further information and supported options, refer to config documentation.