Snapshot And Restore
editSnapshot And Restore
editA snapshot is a backup taken from a running Elasticsearch cluster. You can take a snapshot of individual indices or of the entire cluster and store it in a repository on a shared filesystem, and there are plugins that support remote repositories on S3, HDFS, Azure, Google Cloud Storage and more.
Snapshots are taken incrementally. This means that when creating a snapshot of an index Elasticsearch will avoid copying any data that is already stored in the repository as part of an earlier snapshot of the same index. Therefore it can be efficient to take snapshots of your cluster quite frequently.
Snapshots can be restored into a running cluster via the restore API. When restoring an index it is possible to alter the name of the restored index as well as some of its settings, allowing a great deal of flexibility in how the snapshot and restore functionality can be used.
It is not possible to back up an Elasticsearch cluster simply by taking a copy of the data directories of all of its nodes. Elasticsearch may be making changes to the contents of its data directories while it is running, and this means that copying its data directories cannot be expected to capture a consistent picture of their contents. Attempts to restore a cluster from such a backup may fail, reporting corruption and/or missing files, or may appear to have succeeded having 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
editA 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 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, and snapshots of indices created in 2.x cannot be restored to 6.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.
Repositories
editYou must register a snapshot repository before you can perform snapshot and restore operations. We recommend creating a new snapshot repository for each major version. The valid repository settings depend on the repository type.
If you register same snapshot repository with multiple clusters, only
one cluster should have write access to the repository. All other clusters
connected to that repository should set the repository to readonly
mode.
The snapshot format can change across major versions, so if you have
clusters on different major versions trying to write the same repository,
new snapshots written by one version will not be visible to the other. While
setting the repository to readonly
on all but one of the clusters should work
with multiple clusters differing by one major version, it is not a supported
configuration.
PUT /_snapshot/my_backup { "type": "fs", "settings": { "location": "my_backup_location" } }
To retrieve information about a registered repository, use a GET request:
GET /_snapshot/my_backup
which returns:
{ "my_backup": { "type": "fs", "settings": { "location": "my_backup_location" } } }
To retrieve information about multiple repositories, specify a
a comma-delimited list of repositories. You can also use the * wildcard when
specifying repository names. For example, the following request retrieves
information about all of the snapshot repositories that start with repo
or
contain backup
:
GET /_snapshot/repo*,*backup*
To retrieve information about all registered snapshot repositories, omit the
repository name or specify _all
:
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. In order to register
the shared file system repository it is necessary to mount the same shared filesystem to the same location on all
master and data nodes. This location (or one of its parent directories) must be registered in the path.repo
setting on all master and data nodes.
Assuming that the shared filesystem is mounted to /mount/backups/my_fs_backup_location
, the following setting should
be added to elasticsearch.yml
file:
path.repo: ["/mount/backups", "/mount/longterm_backups"]
The path.repo
setting supports Microsoft Windows UNC paths as long as at least server name and share are specified as
a prefix and back slashes are properly escaped:
path.repo: ["\\\\MY_SERVER\\Snapshots"]
After all nodes are restarted, the following command can be used to register the shared file system repository with
the name my_fs_backup
:
PUT /_snapshot/my_fs_backup { "type": "fs", "settings": { "location": "/mount/backups/my_fs_backup_location", "compress": true } }
If the repository location is specified as a relative path this path will be resolved against the first path specified
in path.repo
:
PUT /_snapshot/my_fs_backup { "type": "fs", "settings": { "location": "my_fs_backup_location", "compress": true } }
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 |
|
Throttles per node restore rate. Defaults to |
|
Throttles per node snapshot rate. Defaults to |
|
Makes repository read-only. 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. |
URL Repository supports the following protocols: "http", "https", "ftp", "file" and "jar". URL repositories with http:
,
https:
, and ftp:
URLs has to be whitelisted by specifying allowed URLs in the repositories.url.allowed_urls
setting.
This setting supports wildcards in the place of host, path, query, and fragment. For example:
repositories.url.allowed_urls: ["http://www.example.org/root/*", "https://*.mydomain.com/*?*#*"]
URL repositories with file:
URLs can only point to locations registered in the path.repo
setting similar to
shared file system repository.
Repository plugins
editOther repository backends are available in these official plugins:
- repository-s3 for S3 repository support
- repository-hdfs for HDFS repository support in Hadoop environments
- repository-azure for Azure storage repositories
- repository-gcs for Google Cloud 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/my_unverified_backup?verify=false { "type": "fs", "settings": { "location": "my_unverified_backup_location" } }
The verification process can also be executed manually by running the following command:
POST /_snapshot/my_unverified_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. Snapshots 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_2?wait_for_completion=true { "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. Before version 1.2.0, the snapshot operation fails if the cluster has any relocating or initializing primaries of indices participating in the snapshot. Starting with version 1.2.0, 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
This command returns basic information about the snapshot including start and end time, version of
Elasticsearch that created the snapshot, the list of included indices, the current state of the
snapshot and the list of failures that occurred during the snapshot. The snapshot state
can be
|
The snapshot is currently running. |
|
The snapshot finished and all shards were stored successfully. |
|
The snapshot finished with an error and failed to store any data. |
|
The global cluster state was stored, but data of at least one shard wasn’t stored successfully.
The |
|
The snapshot was created with an old version of Elasticsearch and therefore is incompatible with the current version of the cluster. |
Similar as for repositories, information about multiple snapshots can be queried in one go, supporting wildcards as well:
GET /_snapshot/my_backup/snapshot_*,some_other_snapshot
All snapshots currently stored in the repository can be listed using the following command:
GET /_snapshot/my_backup/_all
The command fails if some of the snapshots are unavailable. The boolean parameter ignore_unavailable
can be used to
return all snapshots that are currently available.
Getting all snapshots in the repository can be costly on cloud-based repositories,
both from a cost and performance perspective. If the only information required is
the snapshot names/uuids in the repository and the indices in each snapshot, then
the optional boolean parameter verbose
can be set to false
to execute a more
performant and cost-effective retrieval of the snapshots in the repository. Note
that setting verbose
to false
will omit all other information about the snapshot
such as status information, the number of snapshotted shards, etc. The default
value of the verbose
parameter is true
.
A currently running snapshot can be retrieved using the following command:
GET /_snapshot/my_backup/_current
A snapshot can be deleted from the repository using the following command:
DELETE /_snapshot/my_backup/snapshot_2
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 unregistered using the following command:
DELETE /_snapshot/my_backup
When a repository is unregistered, 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 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.
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 (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 an incompatible settings such as discovery.zen.minimum_master_nodes
and as a result disable a smaller cluster until the
required number of master eligible nodes is added. If you need to restore a snapshot with incompatible persistent settings, try
restoring it without the global cluster state.
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.
DELETE /_snapshot/my_backup/snapshot_1
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.
Effect of cluster blocks on snapshot and restore operations
editMany snapshot and restore operations are affected by cluster and index blocks. For example, registering and unregistering repositories require write global metadata access. The snapshot operation requires that all indices and their metadata as well as the global metadata were readable. The restore operation requires the global metadata to be writable, however the index level blocks are ignored during restore because indices are essentially recreated during restore. Please note that a repository content is not part of the cluster and therefore cluster blocks don’t affect internal repository operations such as listing or deleting snapshots from an already registered repository.