Elasticsearch (ES) is a distributed open-source search and analytics engine built on the text search library Apache Lucene. Given enough machines, an ES cluster can typically execute search and aggregation queries across very large datasets. While ES is great if you want traditional full text search over a set of text documents (similar to Google search), it is also very useful for searching and aggregating over large sets of more structured or semi-structured datasets like system logs, network traffic data and collected system metrics.