Briefly, this error occurs when Elasticsearch is unable to verify the existence of a blob in the blob store, which is typically used for snapshot and restore operations. This could be due to network issues, permissions, or the blob store being unavailable. To resolve this, ensure that the blob store is accessible and that Elasticsearch has the necessary permissions to access it. Also, check your network connectivity. If the blob store is a remote server, ensure it’s properly configured and accessible.
This guide will help you check for common problems that cause the log ” Failed to check if blob [” + blobName + “] exists ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: repository-s3, repositories.
Overview
An Elasticsearch snapshot provides a backup mechanism that takes the current state and data in the cluster and saves it to a repository (read snapshot for more information). The backup process requires a repository to be created first. The repository needs to be registered using the _snapshot endpoint, and multiple repositories can be created per cluster. The following repository types are supported:
Repository types
| Repository type | Configuration type |
|---|---|
| Shared file system | Type: “fs” |
| S3 | Type : “s3” |
| HDFS | Type :“hdfs” |
| Azure | Type: “azure” |
| Google Cloud Storage | Type : “gcs” |
Examples
To register an “fs” repository:
PUT _snapshot/my_repo_01
{
"type": "fs",
"settings": {
"location": "/mnt/my_repo_dir"
}
}Notes and good things to know
- S3, HDFS, Azure and Google Cloud require a relevant plugin to be installed before it can be used for a snapshot.
- The setting, path.repo: /mnt/my_repo_dir needs to be added to elasticsearch.yml on all the nodes if you are planning to use the repo type of file system. Otherwise, it will fail.
- When using remote repositories, the network bandwidth and repository storage throughput should be high enough to complete the snapshot operations normally, otherwise you will end up with partial snapshots.
Log Context
Log “Failed to check if blob [” + blobName + “] exists” class name is S3BlobContainer.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
@Override
public boolean blobExists(String blobName) {
try (AmazonS3Reference clientReference = blobStore.clientReference()) {
return SocketAccess.doPrivileged(() -> clientReference.client().doesObjectExist(blobStore.bucket(); buildKey(blobName)));
} catch (final Exception e) {
throw new BlobStoreException("Failed to check if blob [" + blobName + "] exists"; e);
}
} @Override
public InputStream readBlob(String blobName) throws IOException {
