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Snapshot And Restore
editSnapshot And Restore
editThe snapshot and restore module allows to create snapshots of individual indices or an entire cluster into a remote repository. At the time of the initial release only shared file system repository was supported, but now a range of backends are available via officially supported repository plugins.
Repositories
editBefore any snapshot or restore operation can be performed a snapshot repository should be registered in
Elasticsearch. The following command registers a shared file system repository with the name my_backup
that
will use location /mount/backups/my_backup
to store snapshots.
PUT /_snapshot/my_backup { "type": "fs", "settings": { "location": "/mount/backups/my_backup", "compress": true } }
Once a repository is registered, its information can be obtained using the following command:
GET /_snapshot/my_backup
which returns:
{ "my_backup": { "type": "fs", "settings": { "compress": "true", "location": "/mount/backups/my_backup" } } }
If a repository name is not specified, or _all
is used as repository name Elasticsearch will return information about
all repositories currently registered in the cluster:
GET /_snapshot
or
GET /_snapshot/_all
Shared File System Repository
editThe shared file system repository ("type": "fs"
) uses the shared file system to store snapshots. The path
specified in the location
parameter should point to the same location in the shared filesystem and be accessible
on all data and master nodes. The following settings are supported:
|
Location of the snapshots. Mandatory. |
|
Turns on compression of the snapshot files. Compression is applied only to metadata files (index mapping and settings). Data files are not compressed. Defaults to |
|
Big files can be broken down into chunks during snapshotting if needed. The chunk size can be specified in bytes or by
using size value notation, i.e. 1g, 10m, 5k. Defaults to |
Read-only URL Repository
editThe URL repository ("type": "url"
) can be used as an alternative read-only way to access data created by the shared file
system repository. The URL specified in the url
parameter should
point to the root of the shared filesystem repository. The following settings are supported:
|
Location of the snapshots. Mandatory. |
Common Repository Settings
editThe following are common settings applicable for all repository types:
|
Throttles per node restore rate. Defaults to |
|
Throttles per node snapshot rate. Defaults to |
Repository plugins
editOther repository backends are available in these official plugins:
- AWS Cloud Plugin for S3 repositories
- HDFS Plugin for Hadoop environments
- Azure Cloud Plugin for Azure storage repositories
Repository Verification
editWhen a repository is registered, it’s immediately verified on all master and data nodes to make sure that it is functional
on all nodes currently present in the cluster. The verify
parameter can be used to explicitly disable the repository
verification when registering or updating a repository:
PUT /_snapshot/s3_repository?verify=false { "type": "s3", "settings": { "bucket": "my_s3_bucket", "region": "eu-west-1" } }
The verification process can also be executed manually by running the following command:
POST /_snapshot/my_backup/_verify
It returns a list of nodes where repository was successfully verified or an error message if verification process failed.
Snapshot
editA repository can contain multiple snapshots of the same cluster. Snapshot are identified by unique names within the
cluster. A snapshot with the name snapshot_1
in the repository my_backup
can be created by executing the following
command:
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 the memory, which means that in large repositories it may take several seconds (or
even minutes) for this command to return even if the wait_for_completion
parameter is set to false
.
By default a snapshot of all open and started indices in the cluster is created. This behavior can be changed by specifying the list of indices in the body of the snapshot request.
PUT /_snapshot/my_backup/snapshot_1 { "indices": "index_1,index_2", "ignore_unavailable": "true", "include_global_state": false }
The list of indices that should be included into the snapshot can be specified using the indices
parameter that
supports multi index syntax. The snapshot request also supports the
ignore_unavailable
option. Setting it to true
will cause indices that do not exist to be ignored during snapshot
creation. By default, when ignore_unavailable
option is not set and an 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. By default, the entire snapshot will fail if one or more indices participating in the snapshot don’t have
all primary shards available. This behaviour can be changed by setting partial
to true
.
The index snapshot process is incremental. In the process of making the index snapshot Elasticsearch analyses the list of the index files that are already stored in the repository and copies only files that were created or changed since the last snapshot. That allows multiple snapshots to be preserved in the repository in a compact form. Snapshotting process is executed in non-blocking fashion. All indexing and searching operation can continue to be executed against the index that is being snapshotted. However, a snapshot represents the point-in-time view of the index at the moment when snapshot was created, so no records that were added to the index after the snapshot process was started will be present in the snapshot. The snapshot process starts immediately for the primary shards that has been started and are not relocating at the moment. Elasticsearch waits for relocation or initialization of shards to complete before snapshotting them.
Besides creating a copy of each index the snapshot process can also store global cluster metadata, which includes persistent cluster settings and templates. The transient settings and registered snapshot repositories are not stored as part of the snapshot.
Only one snapshot process can be executed in the cluster at any time. While snapshot of a particular shard is being created this shard cannot be moved to another node, which can interfere with rebalancing process and allocation filtering. Elasticsearch will only be able to move a shard to another node (according to the current allocation filtering settings and rebalancing algorithm) once the snapshot is finished.
Once a snapshot is created information about this snapshot can be obtained using the following command:
GET /_snapshot/my_backup/snapshot_1
All snapshots currently stored in the repository can be listed using the following command:
GET /_snapshot/my_backup/_all
A snapshot can be deleted from the repository using the following command:
DELETE /_snapshot/my_backup/snapshot_1
When a snapshot is deleted from a repository, Elasticsearch deletes all files that are associated with the deleted snapshot and not used by any other snapshots. If the deleted snapshot operation is executed while the snapshot is being created the snapshotting process will be aborted and all files created as part of the snapshotting process will be cleaned. Therefore, the delete snapshot operation can be used to cancel long running snapshot operations that were started by mistake.
A repository can be deleted using the following command:
DELETE /_snapshot/my_backup
When a repository is deleted, Elasticsearch only removes the reference to the location where the repository is storing the snapshots. The snapshots themselves are left untouched and in place.
Restore
editA snapshot can be restored using the following command:
POST /_snapshot/my_backup/snapshot_1/_restore
By default, all indices in the snapshot as well as cluster state are restored. It’s possible to select indices that
should be restored as well as prevent 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 index 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": false, "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, 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.
Partial restore
editBy 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.
Changing index settings during restore
editMost 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", "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.
Restoring to a different cluster
editThe 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 than the cluster that was used to create the snapshot.
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. Prior to version 1.5.0 elasticsearch
didn’t check restored persistent settings making it possible to accidentally restore an incompatible
discovery.zen.minimum_master_nodes
setting, and as a result disable a smaller cluster until the required number of
master eligible nodes is added. Starting with version 1.5.0 incompatible settings are ignored.
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.
Snapshot status
editA 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
Multiple ids are also supported:
GET /_snapshot/my_backup/snapshot_1,snapshot_2/_status
Monitoring snapshot/restore progress
editThere are several ways to monitor the progress of the snapshot and restores processes while they are running. Both
operations support wait_for_completion
parameter that would block client until the operation is completed. This is
the simplest method that can be used to get notified about operation completion.
The snapshot operation can be also monitored by periodic calls to the snapshot info:
GET /_snapshot/my_backup/snapshot_1
Please note that snapshot info operation uses the same resources and thread pool as the snapshot operation. So, executing a snapshot info operation while large shards are being snapshotted can cause the snapshot info operation to wait for available resources before returning the result. On very large shards the wait time can be significant.
To get more immediate and complete information about snapshots the snapshot status command can be used instead:
GET /_snapshot/my_backup/snapshot_1/_status
While snapshot info method returns only basic information about the snapshot in progress, the snapshot status returns complete breakdown of the current state for each shard participating in the snapshot.
The restore process piggybacks on the standard recovery mechanism of the Elasticsearch. As a result, standard recovery
monitoring services can be used to monitor the state of restore. When restore operation is executed the cluster
typically goes into red
state. It happens because the restore operation starts with "recovering" primary shards of the
restored indices. During this operation the primary shards become unavailable which manifests itself in the red
cluster
state. Once recovery of primary shards is completed Elasticsearch is switching to standard replication process that
creates the required number of replicas at this moment cluster switches to the yellow
state. Once all required replicas
are created, the cluster switches to the green
states.
The cluster health operation provides only a high level status of the restore process. It’s possible to get more detailed insight into the current state of the recovery process by using indices recovery and cat recovery APIs.
Stopping currently running snapshot and restore operations
editThe snapshot and restore framework allows running only one snapshot or one restore operation at a time. If a currently running snapshot was executed by mistake, or takes unusually long, it can be terminated using the snapshot delete operation. The snapshot delete operation checks if the deleted snapshot is currently running and if it does, the delete operation stops that snapshot before deleting the snapshot data from the repository.
The restore operation uses the standard shard recovery mechanism. Therefore, any currently running restore operation can be canceled by deleting indices that are being restored. Please note that data for all deleted indices will be removed from the cluster as a result of this operation.