We have 15 Nodes cluster where 3 master 12 data Nodes.
After hitting below comand
curl -XGET 'localhost:9200/_cat/shards?h=index,shard,prirep,state,unassigned.reason,unassigned.details'| grep UNASSIGNED
index1 2 r UNASSIGNED CLUSTER_RECOVERED
index1 3 p UNASSIGNED CLUSTER_RECOVERED
index1 3 r UNASSIGNED CLUSTER_RECOVERED
index1 4 p UNASSIGNED CLUSTER_RECOVERED
index1 4 r UNASSIGNED CLUSTER_RECOVERED
index1 1 p UNASSIGNED CLUSTER_RECOVERED
index1 1 r UNASSIGNED CLUSTER_RECOVERED
index1 0 p UNASSIGNED CLUSTER_RECOVERED
index1 0 r UNASSIGNED CLUSTER_RECOVERED
index2 2 p UNASSIGNED CLUSTER_RECOVERED
index2 2 r UNASSIGNED CLUSTER_RECOVERED
index2 3 p UNASSIGNED CLUSTER_RECOVERED
index2 3 r UNASSIGNED CLUSTER_RECOVERED
index2 4 p UNASSIGNED CLUSTER_RECOVERED
index2 4 r UNASSIGNED CLUSTER_RECOVERED
index2 1 p UNASSIGNED CLUSTER_RECOVERED
index2 1 r UNASSIGNED CLUSTER_RECOVERED
index2 0 p UNASSIGNED CLUSTER_RECOVERED
index2 0 r UNASSIGNED CLUSTER_RECOVERED
index3 2 p UNASSIGNED CLUSTER_RECOVERED
index3 2 r UNASSIGNED CLUSTER_RECOVERED
index3 3 p UNASSIGNED CLUSTER_RECOVERED
index3 3 r UNASSIGNED CLUSTER_RECOVERED
index3 4 p UNASSIGNED CLUSTER_RECOVERED
index3 4 r UNASSIGNED CLUSTER_RECOVERED
index3 1 p UNASSIGNED CLUSTER_RECOVERED
index3 1 r UNASSIGNED CLUSTER_RECOVERED
index3 0 p UNASSIGNED CLUSTER_RECOVERED
index3 0 r UNASSIGNED CLUSTER_RECOVERED
No logs are generated on regarding why cluster is not able to assign the above index