Elasticsearch SnapshotMissingException: Snapshot missing - Common Causes & Fixes

Brief Explanation

The "SnapshotMissingException: Snapshot missing" error in Elasticsearch occurs when attempting to access or restore a snapshot that does not exist or has been deleted from the snapshot repository.

Impact

This error can significantly impact data recovery and backup processes, potentially leading to data loss or system downtime if the missing snapshot was crucial for a restore operation.

Common Causes

1. The snapshot was deleted manually or by an automated process.
2. The snapshot repository is corrupted or inaccessible.
3. Incorrect snapshot name or repository name in the restore request.
4. Network issues preventing access to the snapshot repository.
5. Permissions issues on the snapshot repository.

Troubleshooting and Resolution Steps

1. Verify the snapshot name and repository:

   GET /_snapshot/_all
   GET /_snapshot/<repository_name>/_all
   

2. Check if the snapshot exists in the repository:

   GET /_snapshot/<repository_name>/<snapshot_name>
   

3. Ensure the snapshot repository is accessible and not corrupted:

   POST /_snapshot/<repository_name>/_verify
   

4. Review Elasticsearch logs for any related errors or warnings.

5. Check network connectivity between Elasticsearch nodes and the snapshot repository.

6. Verify permissions on the snapshot repository directory.

7. If the snapshot is genuinely missing, restore from an alternative snapshot or recreate the data if possible.

8. Implement regular snapshot verification and testing to prevent future issues.

Best Practices

1. Implement a robust snapshot naming convention and retention policy.
2. Regularly verify and test your snapshots to ensure they are valid and restorable.
3. Use multiple snapshot repositories for redundancy.
4. Monitor snapshot creation and deletion processes.
5. Implement proper access controls and permissions for snapshot repositories.

Frequently Asked Questions

Q: Can I recover a deleted snapshot in Elasticsearch?
A: Generally, once a snapshot is deleted, it cannot be recovered. This is why it's crucial to have a proper backup strategy and retention policy in place.

Q: How can I prevent accidental deletion of important snapshots?
A: Implement strict access controls, use descriptive naming conventions, and consider using snapshot lifecycle management (SLM) policies to automate snapshot creation and deletion.

Q: What should I do if all my snapshots are missing?
A: First, verify the repository is accessible and not corrupted. If the snapshots are genuinely gone, you may need to rebuild your indices from the original data source or use any available replicas.

Q: Can network issues cause the SnapshotMissingException?
A: Yes, if Elasticsearch cannot access the snapshot repository due to network issues, it may report snapshots as missing. Always check network connectivity when troubleshooting this error.

Q: How often should I create and verify snapshots in Elasticsearch?
A: The frequency depends on your data change rate and recovery point objective (RPO). Generally, daily snapshots with weekly verification is a good starting point, but adjust based on your specific needs and resources.