The configuration of the ElasticSearchLookupService Controler Service is pretty straight forward as you have noticed. It uses another controller service, a ElasticSearchClientServiceImpl service, to connect to the Elastic service.
Most of the connectivity details need to be specified on the ElasticSearchClientServiceImpl service configuration.
The best place for reference is the documentation:
Was your question answered? Please take some time to click on "Accept as Solution" below this post.
If you find a reply useful, say thanks by clicking on the thumbs up button.