Elasticsearch is nowadays one of the most widely used and deployed full text search engines containing a large amount of capabilities. How how are they actually implemented and how does Elasticsearch operate behind the scenes ? This session will reveal the innerworkings behind the core capabilities of Elasticsearch. We will provide a review of Elasticsearch architecture and general structure of the public Apache 2.0 codebase. Further expanding on that knowledge we will develop a relatively simple ingest plugin in Java that filters certain keywords from indexed documents.