[[snapshots-take-snapshot]]
== Create a snapshot

A repository can contain multiple snapshots of the same cluster. Snapshots are identified by unique names within the
cluster.

Use the <<put-snapshot-repo-api,create or update snapshot repository API>> to
register or update a snapshot repository, and then use the
<<create-snapshot-api,create snapshot API>> to create a snapshot in a
repository.

The following request creates a snapshot with the name `snapshot_1` in the repository `my_backup`:

////
[source,console]
-----------------------------------
PUT /_snapshot/my_backup
{
  "type": "fs",
  "settings": {
    "location": "my_backup_location"
  }
}
-----------------------------------
// TESTSETUP
////

[source,console]
-----------------------------------
PUT /_snapshot/my_backup/snapshot_1?wait_for_completion=true
-----------------------------------

The `wait_for_completion` parameter specifies whether or not the request should return immediately after snapshot
initialization (default) or wait for snapshot completion. During snapshot initialization, information about all
previous snapshots is loaded into memory, which means that in large repositories it may take several seconds (or
even minutes) for this request to return even if the `wait_for_completion` parameter is set to `false`.

By default, a snapshot backs up all data streams and open indices in the cluster. You can change this behavior by
specifying the list of data streams and indices in the body of the snapshot request:

[source,console]
-----------------------------------
PUT /_snapshot/my_backup/snapshot_2?wait_for_completion=true
{
  "indices": "data_stream_1,index_1,index_2",
  "ignore_unavailable": true,
  "include_global_state": false,
  "metadata": {
    "taken_by": "kimchy",
    "taken_because": "backup before upgrading"
  }
}
-----------------------------------
// TEST[skip:cannot complete subsequent snapshot]

Use the `indices` parameter to list the data streams and indices that should be included in the snapshot. This parameter supports
<<multi-index,multi-target syntax>>, although the options that control the behavior of multi-index syntax
must be supplied in the body of the request, rather than as request parameters.

Data stream backups include the stream's backing indices and metadata, such as
the current <<data-streams-generation,generation>> and timestamp field.

You can also choose to include only specific backing indices in a snapshot.
However, these backups do not include the associated data stream's
metadata or its other backing indices.

Snapshots can also include a data stream but exclude specific backing indices.
When you restore the data stream, it will contain only backing indices present
in the snapshot. If the stream's original write index is not in the snapshot,
the most recent backing index from the snapshot becomes the stream's write index.

[discrete]
[[create-snapshot-process-details]]
=== Snapshot process details

The snapshot process works by taking a byte-for-byte copy of the files that
make up each index or data stream and placing these copies in the repository.
These files are mostly written by Lucene and contain a compact representation
of all the data in each index or data stream in a form that is designed to be
searched efficiently. This means that when you restore an index or data stream
from a snapshot there is no need to rebuild these search-focused data
structures. It also means that you can use <<searchable-snapshots>> to directly
search the data in the repository.

The snapshot process is incremental: {es} compares the files that make up the
index or data stream against the files that already exist in the repository
and only copies files that were created or changed
since the last snapshot. Snapshots are very space-efficient since they reuse
any files copied to the repository by earlier snapshots.

Snapshotting does not interfere with ongoing indexing or searching operations.
A snapshot captures a view of each shard at some point in time between the
start and end of the snapshotting process. The snapshot may not include
documents added to a data stream or index after the snapshot process starts.

You can start multiple snapshot operations at the same time. Concurrent snapshot
operations are limited by the `snapshot.max_concurrent_operations` cluster
setting, which defaults to `1000`. This limit applies in total to all ongoing snapshot
creation, cloning, and deletion operations. {es} will reject any operations
that would exceed this limit.

The snapshot process starts immediately for the primary shards that have been
started and are not relocating at the moment. {es} waits for relocation or
initialization of shards to complete before snapshotting them.

Besides creating a copy of each data stream and index, the snapshot process can
also store global cluster metadata, which includes persistent cluster settings,
templates, and data stored in system indices, such as Watches and task records,
regardless of whether those system indices are named in the `indices` section
of the request. You can also use the create snapshot
API's <<create-snapshot-api-feature-states,`feature_states`>> parameter to
include only a subset of system indices in the snapshot. Snapshots do not
store transient settings or registered snapshot repositories.

While a snapshot of a particular shard is being created, the shard cannot be
moved to another node, which can interfere with rebalancing and allocation
filtering. {es} can only move the shard to another node (according to the current
allocation filtering settings and rebalancing algorithm) after the snapshot
process is finished.

You can use the <<get-snapshot-api,Get snapshot API>> to retrieve information
about ongoing and completed snapshots. See
<<snapshots-monitor-snapshot-restore,Monitor snapshot and restore progress>>.

[discrete]
[[create-snapshot-options]]
=== Options for creating a snapshot
The create snapshot request supports the
`ignore_unavailable` option. Setting it to `true` will cause data streams and indices that do not exist to be ignored during snapshot
creation. By default, when the `ignore_unavailable` option is not set and a data stream or index is missing, the snapshot request will fail.

By setting `include_global_state` to `false` it's possible to prevent the cluster global state to be stored as part of
the snapshot.

IMPORTANT: The global cluster state includes the cluster's index
templates, such as those <<create-index-template,matching a data
stream>>. If your snapshot includes data streams, we recommend storing the
global state as part of the snapshot. This lets you later restored any
templates required for a data stream.

By default, the entire snapshot will fail if one or more indices participating in the snapshot do not have
all primary shards available. You can change this behaviour by setting `partial` to `true`. The `expand_wildcards`
option can be used to control whether hidden and closed indices will be included in the snapshot, and defaults to `all`.

Use the `metadata` field to attach arbitrary metadata to the snapshot,
such as who took the snapshot,
why it was taken, or any other data that might be useful.

Snapshot names can be automatically derived using <<date-math-index-names,date math expressions>>, similarly as when creating
new indices. Special characters must be URI encoded.

For example, use the <<create-snapshot-api,create snapshot API>> to create
a snapshot with the current day in the name, such as `snapshot-2020.07.11`:

[source,console]
-----------------------------------
PUT /_snapshot/my_backup/<snapshot-{now/d}>
PUT /_snapshot/my_backup/%3Csnapshot-%7Bnow%2Fd%7D%3E
-----------------------------------
// TEST[continued]

NOTE: You can also create snapshots that are copies of part of an existing snapshot using the <<clone-snapshot-api,clone snapshot API>>.
