Elasticsearch Architecture

- An elasticsearch cluster is made up of number of nodes.
- Each node is nothing but an instance of elasticsearch.
- The data in elasticsearch is stored in index, you can compare it as database in relational database.
- The index can have any limit of data but this can create problem while operation as the index is large.
- Now, to deal with this situation a shard needs to be created as a unit of data that represents a subset of a larger index. There can be more than one shard for an index.
- Shard contains data represented as documents. 
- Documents can be compared with rows in relational database.