Ealasticsearch Tutorial:
https://www.toptal.com/dot-net/elasticsearch-dot-net-developers
Vulcan is an EPiServer lightweight (free) alternative to EPiServer find, based on Elasticsearch as well:
https://world.episerver.com/blogs/Dan-Matthews/Dates/2016/4/introducing-vulcan-the-lightweight-elasticsearch-client-for-episerver/
https://world.episerver.com/blogs/Dan-Matthews/Dates/2017/1/vulcan-comes-of-age/