In an ELK cluster, does master node and data node keep same copy of shards? In case of failure of master node or data node, will we have a copy of indices on the other node? Like if master is lost, will i be able to use Kibana to use data node for elastic search. I guess here is what i need to learn from this discussion, If i have 1 data and 1 master node will it make the indices replicated to both master and data node? Is 2 node cluster a good practice?
Master and data are just roles that a node can have, and nodes does not need to have just one. For smaller clusters i would recommend setting up 3 nodes that have the default set of roles (all). This means that all of them hold data and all are master eligible and allow you to have an operational cluster even if you lose 1 node.
2 nodes does not give you high availability as Elasticsearch requires at least 3 master eligible nodes for that.