how we decide in which node we should store document in elasticsearch?

Question

Since i am a new in ES, i need help.

I read that it is possible to specify the shard where the document to be stored using 'routing'. But is it possible to restrict that a document should be saved in a particular node?..

Suppose i have two nodes. Node1 and node2. my requirement is that, if i add a document from node1 to index 'attenadance', it should store primary shard at node1 and the replica may be at node2. And the same thing if i add a document from node2 to index 'attenadance', it should store primary shard at node2 and the replica may be at node1...Please advice me is it possible in ES?..if yes, please tell how to achieve this in ES.

Answer 1

You don't control where shards/replicas go -- elasticsearch handles that... In general, it won't put a replica of a shard on the same node. There is a really good explanation of how it all works here: Shards and replicas in Elasticsearch

There is also good documentation on using shard routing on the elasticsearch blog if you need to group data together (but be careful because it can generate hot-spots.

Answer 2

Each node has a specific value associated with rack in cofig.yml. Node 1 has a setting node.rack: rack1, Node 2 a setting of node.rack: rack2, and so on.

We can create an index that will only deploy on nodes that have rack set to rack1 setting index.routing.allocation.include.tag to rack1. For example:

curl -XPUT localhost:9200/test/_settings -d '{
    "index.routing.allocation.include.tag" : "rack1"
}'

further ref: Elasticsearch official doc