CSS provides functions on a per cluster basis. A cluster represents an independent search service that contains multiple nodes.
Index is similar to "database" in the relational database (RDB) and stores Elasticsearch data. It refers to a logical space that consists of one or more shards.
A replica is a copy of the actual storage index in a shard. It can be understood as a backup of the shard. Replicas help prevent single point of failures (SPOFs). You can increase or decrease the number of replicas based on your service requirements.
An entity for Elasticsearch storage. Equivalent to a row in the RDB, the document is the basic unit that can be indexed.
Similar to a table in the RDB, type is used to distinguish between different data. One index can contain multiple document types. A document must be indexed to a document type inside an index.
A mapping is used to restrict the type of a field and is automatically created based on data. It is similar to a schema in the database.
Minimum unit of a document. A field is similar to a column in a database.