A snapshot is a backup taken from a running Elasticsearch cluster. You can take snapshots of individual indices or of the entire cluster. Snapshots can be stored in either local or remote repositories. Remote repositories can reside on S3, HDFS, Azure, Google Cloud Storage, and other platforms supported by a repository plugin.
Snapshots are incremental: each snapshot of an index only stores data that is not part of an earlier snapshot. This enables you to take frequent snapshots with minimal overhead.
You can restore snapshots to a running cluster with the restore API. By default, all indices in the snapshot are restored. Alternatively, you can restore specific indices or restore the cluster state from a snapshot. When restoring indices, you can modify the index name and selected index settings.
You can use snapshot lifecycle management to automatically take and manage snapshots.
You cannot back up an Elasticsearch cluster by simply copying the data directories of all of its nodes. Elasticsearch may be making changes to the contents of its data directories while it is running; copying its data directories cannot be expected to capture a consistent picture of their contents. If you try to restore a cluster from such a backup, it may fail and report corruption and/or missing files. Alternatively, it may appear to have succeeded though it silently lost some of its data. The only reliable way to back up a cluster is by using the snapshot and restore functionality.
Version compatibility refers to the underlying Lucene index compatibility. Follow the Upgrade documentation when migrating between versions.
A snapshot contains a copy of the on-disk data structures that make up an index. This means that snapshots can only be restored to versions of Elasticsearch that can read the indices:
- A snapshot of an index created in 6.x can be restored to 7.x.
- A snapshot of an index created in 5.x can be restored to 6.x.
- A snapshot of an index created in 2.x can be restored to 5.x.
- A snapshot of an index created in 1.x can be restored to 2.x.
Conversely, snapshots of indices created in 1.x cannot be restored to 5.x or 6.x, snapshots of indices created in 2.x cannot be restored to 6.x or 7.x, and snapshots of indices created in 5.x cannot be restored to 7.x or 8.x.
Each snapshot can contain indices created in various versions of Elasticsearch, and when restoring a snapshot it must be possible to restore all of the indices into the target cluster. If any indices in a snapshot were created in an incompatible version, you will not be able restore the snapshot.
When backing up your data prior to an upgrade, keep in mind that you won’t be able to restore snapshots after you upgrade if they contain indices created in a version that’s incompatible with the upgrade version.
If you end up in a situation where you need to restore a snapshot of an index that is incompatible with the version of the cluster you are currently running, you can restore it on the latest compatible version and use reindex-from-remote to rebuild the index on the current version. Reindexing from remote is only possible if the original index has source enabled. Retrieving and reindexing the data can take significantly longer than simply restoring a snapshot. If you have a large amount of data, we recommend testing the reindex from remote process with a subset of your data to understand the time requirements before proceeding.