Elasticsearch is a search server based on Lucene. It provides a full-text search engine with distributed multi-user function based on RESTful web interface. Elasticsearch is developed in Java language and released as open source under the Apache license. It is a popular enterprise search engine.

Using Elasticsearch in cloud computing can realize real-time search, which is stable, reliable, fast and easy to install and use. The official client provides a Java version. NET(C#), PHP, Python, Apache Groovy, Ruby and many other languages. According to the ranking of DB-Engines, Elasticsearch is the most popular enterprise search engine, followed by Apache Solr, which is also based on Lucene.

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Elasticsearch can be used to search various documents. It provides extensible search, has near real-time search and supports multi-tenancy. Elasticsearch is distributed, which means that the index can be divided into fragments, and each fragment can have zero or more copies. Each node hosts one or more slices and acts as a coordinator, delegating operations to the correct slices.

Rebalancing and routing are done automatically. Related data is usually stored in the same index, which consists of one or more master slices and zero or more duplicate slices. Once the index is created, the number of master slices cannot be changed.