Elasticsearch Snapshot



Elasticsearch Snapshot

Opster Team

July 2020, Version: 1.7-8.0


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Snaphshots in Elasticsearch

What it is

An Elasticsearch snapshot is a backup of an index taken from a running cluster. Snapshots are taken incrementally, i.e. when it creates a snapshot of an index, Elasticsearch will not copy any data that is already stored in the elasticsearch repository as part of an earlier snapshot of the index (for the one that is already completed with no further writes ). Therefore you can take snapshots quite often and efficiently.

You can restore snapshots into a running cluster via the restore API. Snapshots can only be restored to versions of Elasticsearch that can read the indices. Check the version compatibility before you restore. You can’t restore an index to a cluster that is more than one version above the index version.

The following repository types are supported:

  • File System Location

  • S3 Object Storage 

  • HDFS

  • Azure, and Google Cloud Storage

Examples: 

An example of using S3 repository for Elasticsearch

PUT _snapshot/backups
{
    "type": "s3",
    "settings": {
      "bucket": "elastic",
      "endpoint": "10.3.10.10:9000",
      "protocol": "http"
    }
}

You will also need to set the S3 access key and secret key in Elasticsearch key store.

bin/elasticsearch-keystore add s3.client.default.access_key
bin/elasticsearch-keystore add s3.client.default.secret_key

Taking a snapshot:
Once the repo is set, taking a snapshot is just an API call.

PUT /_snapshot/backup/my_snapshot-01-10-2019

Where backup is the name of snapshot repo, and my_snapshot-01-10-2019 is the name of the snapshot. The above example will take a snapshot of all the indices. To take a snapshot of specific indices, you can provide the names of those indices. 

PUT /_snapshot/backup/my_snapshot-01-10-2019
{
  "indices": "my_index_1,my_index_2"
  }
}

Restoring a Snapshot:
Restoring from a snapshot is also an API call:

POST /_snapshot/backup/my_snapshot-01-10-2019
/_restore
{
  "indices": "index_1,index_2"
}

This will restore index_1 and index_2 from the snapshot my_snapshot-01-10-2019 in backup repository.

Notes and good things to know :
  • Snapshot repository needs to be set up before you can take a snapshot, and you will need to install the S3 repository plugin as well if you plan to use a repository with S3 as backend storage.

sudo bin/elasticsearch-plugin install repository-s3
  • You can use curator_cli tool to automate taking snapshots such as cron , jenkins or kubernetes job schedule

  • It is better to use Elasticsearch snapshots instead of disk backups/snapshots.

  • If you are going to restore an index that already exists ( because it may have incomplete data or have gone corrupt  ), the restore will fail until you either close the index first or delete it.

  • Snapshot and restore mechanism can also be used to copy data from one cluster to another cluster.

  • If you don’t have S3 storage , you can run minio with NFS backend to create an S3 equivalent for your cluster snapshots.

Common Problems 
  • When taking snapshots or restoring to remote repositories on low bandwidth, or when having a repository storage with low throughput, the snapshot may fail due to timeouts and hence it will result in partial snapshots as shown below. 
  • Retrying the snapshot operation again (and perhaps several times ) will finally result in a complete snapshot and relatively faster as compared to initial snapshot as it will just try to back up the failed shards only on each re-try. It’s better to have the snapshot repo on local network with elasticsearch or configure/design the repository for high write throughput so that you don’t have to deal with partial snapshots.

  • The snapshot operation will fail if there is some missing index. By setting the ignore_unavailable option to true will cause indices that do not exist to be ignored during snapshot operation. 

  • If you are using some open source security tool such as SearchGuard, you will need to configure the elasticsearch snapshot restore settings on the cluster before you can restore any snapshot. 

  • In elasticsearch.yml

searchguard.enable_snapshot_restore_privilege: true

Related log errors to this ES concept


Failed to close snapshot in repository
Failed to create snapshot no longer a master
Failed to update snapshot state
Reverting to snapshot
Failed to delete shard snapshot file
Deleted snapshot failed deleting files
Failed to clean up abandoned snapshot in INIT state
Failed to create snapshot
Failed to finalize snapshot
Failed to get snapshot
Failed to notify listeners
Failed to update restore state

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