How To Solve Issues Related to Log – Failed to get snapshot

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Updated: Dec-19

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Troubleshooting background

To troubleshoot Elasticsearch log “Failed to get snapshot” it’s important to understand common problems related to Elasticsearch concepts: snapshot. See detailed explanations below complete with common problems, examples and useful tips.

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

Cluster in Elasticsearch

What is it

In Elasticsearch a cluster is a collection of one or more nodes (servers / VMs). A cluster can consist of an unlimited number of nodes. The cluster provides interface for indexing and storing data and search capability across all of the data which is stored in the data nodes

Each cluster has a single master node that is elected by the master eligible nodes. In cases where the master is not available the other connected master eligible nodes elect a new master. Clusters are identified by a unique name, which defaults to “Elasticsearch”.

Nodes in Elasticsearch

What it is

Simply explained a node is a single server that is part of a cluster. Each node is assigned with one or more roles, which describes the node responsibility and operations – Data nodes stores the data, and participates in the cluster’s indexing and search capabilities, while master nodes are responsible for managing the cluster activities and storing the cluster state, including the metadata.

While it’s possible to run several Node instances of Elasticsearch on the same hardware, it’s considered a best practice to limit a server to a single running instance of Elasticsearch.

Nodes connect to each other and form a cluster by using a discovery method. 

Roles
Master node

Master nodes are in charge of cluster-wide settings and changes  – deleting or creating indices and fields, adding or removing nodes and allocating shards to nodes. Each cluster has a single master node that is elected from the master eligible nodes using a distributed consensus algorithm and is reelected if the current master node fails.

Coordinator Node (aka client node)

Coordinator Node – is a node that does not hold any configured role. It doesn’t hold data, not part of the master eligible group nor execute ingest pipelines. Coordinator node serves incoming search requests and is acting as the query coordinator – running the query and fetch phases, sending requests to every node which holds a shard being queried. The client node also distributes bulk indexing operations and route queries to shards copies based on the nodes responsiveness.


To help troubleshoot related issues we have gathered selected Q&A from the community and issues from Github , please review the following for further information :

1 Snapshot Creation Error In S3 Repo  

2Snapshot To Aws S3 Failing Es 1 2 2  

Snapshot And Restore S3 And Glacier


Log Context

Log ”Failed to get snapshot [{}]” classname is SnapshotsService.java
We have extracted the following from Elasticsearch source code to get an in-depth context :

                }
            } catch (Exception ex) {
                if (ignoreUnavailable) {
                    logger.warn(() -> new ParameterizedMessage("failed to get snapshot [{}]"; snapshotId); ex);
                } else {
                    if (ex instanceof SnapshotException) {
                        throw ex;
                    }
                    throw new SnapshotException(repositoryName; snapshotId; "Snapshot could not be read"; ex);                 } else {
                    snapshotSet.add(repository.getSnapshotInfo(snapshotId));



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