Elasticsearch IndexNotFoundException: Index not found

Brief Explanation

The "IndexNotFoundException: Index not found" error in Elasticsearch occurs when an operation is attempted on an index that does not exist in the cluster. This error indicates that the specified index is missing or has been deleted.

Common Causes

1. Incorrect index name in the query or API call
2. Index has been deleted or not yet created
3. Typos in index patterns or wildcards
4. Insufficient permissions to access the index
5. Index lifecycle management (ILM) policies that have removed the index

Troubleshooting and Resolution Steps

1. Verify index existence:

   • Use the GET /_cat/indices API to list all available indices
   • Check if the index name is correct and exists in the list

2. Check index naming:

   • Ensure the index name is lowercase (Elasticsearch index names are case-sensitive)
   • Verify there are no typos in the index name or pattern

3. Review index patterns:

   • If using wildcards, ensure they are correctly formatted
   • Check if the pattern matches any existing indices

4. Examine permissions:

   • Verify that the user or role has the necessary permissions to access the index
   • Review cluster security settings and index-level access controls

5. Investigate index lifecycle:

   • Check if any ILM policies are affecting the index
   • Review index retention policies and rollover configurations

6. Create the index:

   • If the index should exist but doesn't, create it using the PUT /<index_name> API

7. Check aliases:

   • Verify if you're trying to access an alias instead of an actual index
   • Use GET /_alias to list all aliases and their associated indices

8. Examine cluster health:

   • Use GET /_cluster/health to ensure the cluster is in a healthy state
   • Check for any ongoing shard allocations or recoveries

Additional Information and Best Practices

• Implement a naming convention for indices to avoid confusion and typos
• Use index templates to automatically apply settings and mappings to new indices
• Regularly monitor and maintain your indices using tools like Curator or ILM
• Implement proper error handling in your applications to gracefully manage index-related errors
• Consider using aliases for common operations to provide an abstraction layer over your indices

Frequently Asked Questions

Q: Can a deleted index be recovered in Elasticsearch?
A: Generally, once an index is deleted, it cannot be directly recovered. However, if you have regular snapshots of your indices, you can restore the deleted index from a snapshot.

Q: How can I prevent accidental index deletion?
A: You can use the index write protection feature by setting index.blocks.write: true in the index settings. Additionally, implement proper access controls and use aliases to abstract direct index operations.

Q: What's the difference between an index not found error and a no shard available error?
A: An "index not found" error occurs when the specified index doesn't exist at all. A "no shard available" error happens when the index exists, but its shards are not available, possibly due to node failures or allocation issues.

Q: Can wildcard patterns cause an index not found error?
A: Yes, if a wildcard pattern doesn't match any existing indices, it can result in an "index not found" error. Always ensure your patterns match at least one existing index.

Q: How does Elasticsearch handle requests to multiple indices if one doesn't exist?
A: By default, Elasticsearch will return an error if any of the specified indices don't exist. You can use the ignore_unavailable=true parameter in your request to skip non-existent indices and continue with the available ones.