About Elasticsearch
The distributed search and analytics engine on top of Apache Lucene.
Elasticsearch was started in 2010 by Shay Banon, built on the Apache Lucene search library and exposed through a JSON over HTTP API. The company behind it, Elastic NV, listed on the NYSE in October 2018 under the ticker $ESTC and is headquartered in Mountain View. The engine is the core of the Elastic Stack, where Logstash and Beats handle ingest and Kibana handles the UI, the combination most people still call ELK.
Inside the cluster, data lives in indices, which are split into shards and copied into replicas across nodes. Documents are JSON, mappings define how fields are analysed, and the Query DSL covers everything from a basic match to fuzzy, geo and nested queries. Aggregations turn the same indices into an analytics surface for log, metric and event data, which is why the ELK stack became the default observability pattern for a generation of engineering teams. Since 8.x, dense-vector fields and a kNN search API made Elasticsearch a credible store for semantic and hybrid search next to BM25. The licensing story to be aware of: in 2021 Elastic moved from Apache 2.0 to a dual SSPL plus Elastic License v2, which prompted AWS to fork the engine as OpenSearch, and in 2024 Elastic added AGPLv3 as a third option to make the source open-source again under OSI terms. We treat the cluster as a destination, land the data on a cadence the cluster can absorb, and shape mappings and shards to the workload instead of the default.