Elastic search shard allocation

Question

What will happen when a node which was moved out of the cluster rejoins the cluster after the cluster re balance?

suppose i have cluster of 5 nodes and its status is green and out of 5 one node leaves the cluster and i have configured delayed shard allocation. After the shard time out of the delayed allocation the master promotes the one of the replica as a primary and allocates the unassigned shards and re balances the cluster. What will happen when a the node which has moved out of the cluster rejoins the cluster after all the re balancing of the cluster has been done? what about the shards present in the node which has rejoined the cluster?

Answer 1

Every Node in your cluster computes a weight based on the amount of shards it holds. You can tune the point at which a rebalancing happens via Cluster Level Shard Allocation Settings. Take note that the important information is the amount of shards, not their size. If your shards are very different in size, this may lead to problems with balancing.

When a Node rejoins the cluster, currently ongoing recovery processes (copying the shard to another node to regain green status, amount limited by cluster.routing.allocation.node_concurrent_recoveries) will complete, then the next shard will be recovered. When the cluster discovers an up-to-date version of the missing shard on your rejoined node it will save that information to cluster state and not take any unneccesary action.