If Elasticsearch encounters index data that is absent from the current cluster state, those indices are considered to be dangling. For example, this can happen if you delete more than cluster.indices.tombstones.size indices while an Elasticsearch node is offline.

Use this API to list dangling indices, which you can then import or delete.

The API returns the following response:

{
  "dangling_indices": [
   {
    "index_name": "my-index-000001",
    "index_uuid": "zmM4e0JtBkeUjiHD-MihPQ",
    "creation_date_millis": 1589414451372,
    "node_ids": [
      "pL47UN3dAb2d5RCWP6lQ3e"
    ]
   }
  ]
}