Restore indices from a snapshot

A snapshot can be restored using the following command:

POST /_snapshot/my_backup/snapshot_1/_restore

By default, all indices in the snapshot are restored, and the cluster state is not restored. It’s possible to select indices that should be restored as well as to allow the global cluster state from being restored by using indices and include_global_state options in the restore request body. The list of indices supports multi index syntax. The rename_pattern and rename_replacement options can be also used to rename indices on restore using regular expression that supports referencing the original text as explained here. Set include_aliases to false to prevent aliases from being restored together with associated indices

POST /_snapshot/my_backup/snapshot_1/_restore
{
  "indices": "index_1,index_2",
  "ignore_unavailable": true,
  "include_global_state": true,
  "rename_pattern": "index_(.+)",
  "rename_replacement": "restored_index_$1"
}

The restore operation can be performed on a functioning cluster. However, an existing index can be only restored if it’s closed and has the same number of shards as the index in the snapshot. The restore operation automatically opens restored indices if they were closed and creates new indices if they didn’t exist in the cluster. If cluster state is restored with include_global_state (defaults to false), the restored templates that don’t currently exist in the cluster are added and existing templates with the same name are replaced by the restored templates. The restored persistent settings are added to the existing persistent settings.

By default, the entire restore operation will fail if one or more indices participating in the operation don’t have snapshots of all shards available. It can occur if some shards failed to snapshot for example. It is still possible to restore such indices by setting partial to true. Please note, that only successfully snapshotted shards will be restored in this case and all missing shards will be recreated empty.

Most of index settings can be overridden during the restore process. For example, the following command will restore the index index_1 without creating any replicas while switching back to default refresh interval:

POST /_snapshot/my_backup/snapshot_1/_restore
{
  "indices": "index_1",
  "ignore_unavailable": true,
  "index_settings": {
    "index.number_of_replicas": 0
  },
  "ignore_index_settings": [
    "index.refresh_interval"
  ]
}

Please note, that some settings such as index.number_of_shards cannot be changed during restore operation.

The information stored in a snapshot is not tied to a particular cluster or a cluster name. Therefore it’s possible to restore a snapshot made from one cluster into another cluster. All that is required is registering the repository containing the snapshot in the new cluster and starting the restore process. The new cluster doesn’t have to have the same size or topology. However, the version of the new cluster should be the same or newer (only 1 major version newer) than the cluster that was used to create the snapshot. For example, you can restore a 1.x snapshot to a 2.x cluster, but not a 1.x snapshot to a 5.x cluster.

If the new cluster has a smaller size additional considerations should be made. First of all it’s necessary to make sure that new cluster have enough capacity to store all indices in the snapshot. It’s possible to change indices settings during restore to reduce the number of replicas, which can help with restoring snapshots into smaller cluster. It’s also possible to select only subset of the indices using the indices parameter.

If indices in the original cluster were assigned to particular nodes using shard allocation filtering, the same rules will be enforced in the new cluster. Therefore if the new cluster doesn’t contain nodes with appropriate attributes that a restored index can be allocated on, such index will not be successfully restored unless these index allocation settings are changed during restore operation.

The restore operation also checks that restored persistent settings are compatible with the current cluster to avoid accidentally restoring incompatible settings. If you need to restore a snapshot with incompatible persistent settings, try restoring it without the global cluster state.

A list of currently running snapshots with their detailed status information can be obtained using the following command:

GET /_snapshot/_status

In this format, the command will return information about all currently running snapshots. By specifying a repository name, it’s possible to limit the results to a particular repository:

GET /_snapshot/my_backup/_status

If both repository name and snapshot id are specified, this command will return detailed status information for the given snapshot even if it’s not currently running:

GET /_snapshot/my_backup/snapshot_1/_status

The output looks similar to the following:

{
  "snapshots": [
    {
      "snapshot": "snapshot_1",
      "repository": "my_backup",
      "uuid": "XuBo4l4ISYiVg0nYUen9zg",
      "state": "SUCCESS",
      "include_global_state": true,
      "shards_stats": {
        "initializing": 0,
        "started": 0,
        "finalizing": 0,
        "done": 5,
        "failed": 0,
        "total": 5
      },
      "stats": {
        "incremental": {
          "file_count": 8,
          "size_in_bytes": 4704
        },
        "processed": {
          "file_count": 7,
          "size_in_bytes": 4254
        },
        "total": {
          "file_count": 8,
          "size_in_bytes": 4704
        },
        "start_time_in_millis": 1526280280355,
        "time_in_millis": 358
      }
    }
  ]
}

The output is composed of different sections. The stats sub-object provides details on the number and size of files that were snapshotted. As snapshots are incremental, copying only the Lucene segments that are not already in the repository, the stats object contains a total section for all the files that are referenced by the snapshot, as well as an incremental section for those files that actually needed to be copied over as part of the incremental snapshotting. In case of a snapshot that’s still in progress, there’s also a processed section that contains information about the files that are in the process of being copied.

Multiple ids are also supported:

GET /_snapshot/my_backup/snapshot_1,snapshot_2/_status