Elasticsearch is a search server for full-text searches built on Apache Lucene. Elasticsearch provides a REST API for indexing and searching. As a managed service, Elasticsearch can be run on a single server or as a cluster. Cluster mode offers the following benefits:
- The search and indexing query load is distributed across various nodes.
- Data replication increases the level of fail-safe operation.
- The amount of available storage space can be increased by adding servers.
Elasticsearch is available via HTTP on port 9200. Access is limited to the host itself (localhost). It can be individually configured and tailored to the application in question.
An entire Elasticsearch index with any number of indices is always available. Individual indices can also be created, managed and deleted with the REST API. The number of replica shards can be individually configured; the default setting is the value corresponding to the cluster quorum. The replica value must always be smaller than the number on the cluster server to guarantee replication.