Elasticsearch works as a cluster, so the data is shared across all (data) nodes that are in that cluster. If the node you talk to doesn't have the data you want, then it will retrieve it from the node that does and then return that to the client.
Coordinating nodes are used to reduce the load on data nodes. They are usually only needed for high volume clusters.
@warkolm : I am not creating any replica, I believe ELK must be creating it.
I have done testing with light load(100 records). While inserting the data there were 3 active data nodes in the cluster, after inserting I kept one active and two were down. Even two of the three were down, I was able to display correct and complete data
Can you tell me case when we don't have any replicas?
This is not good. You should always aim to have at least 3 master eligible nodes in any cluster. Two nodes does not give any high availability as Elasticsearch uses consensus algorithms and require a strict majority of master eligible nodes to be available to function fully.
Just because you can have dedicated node types does not mean that you should. The easiest way to get started is to have 3 nodes that hold data and are master eligible. Unless you expect to significantly expand the cluster this is a configuration that suits a large number of users.
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