The http.max_header_size setting in Elasticsearch controls the maximum size of HTTP headers allowed in client requests. This setting helps prevent potential denial-of-service attacks and ensures proper resource allocation for handling incoming HTTP requests.
Description
- Default value: 8KB
- Possible values: Any positive integer followed by a size unit (e.g., 8kb, 16kb, 1mb)
- Recommendation: Keep the default value unless you have specific requirements for larger headers
The http.max_header_size setting limits the total size of all HTTP headers in a single request. If a request exceeds this limit, Elasticsearch will reject it with a 400 Bad Request error. This setting is crucial for maintaining the stability and security of your Elasticsearch cluster by preventing excessively large headers from consuming too much memory or processing power.
Example
To change the http.max_header_size setting using the cluster settings API:
PUT _cluster/settings
{
"persistent": {
"http.max_header_size": "16kb"
}
}
You might want to increase this value if you're working with applications that send large amounts of data in HTTP headers, such as authentication tokens or complex query parameters. However, be cautious when increasing this value, as it can potentially expose your cluster to security risks or performance issues.
Common Issues and Misuses
- Setting the value too low can cause legitimate requests with large headers to fail
- Setting the value too high may expose the cluster to potential denial-of-service attacks
- Forgetting to account for this setting when designing client applications that send large headers
Do's and Don'ts
Do's:
- Monitor your cluster logs for any 400 Bad Request errors related to header size
- Adjust the setting gradually if needed, and test thoroughly after each change
- Consider alternative methods for passing large amounts of data, such as request bodies instead of headers
Don'ts:
- Don't set an excessively high value without careful consideration of security implications
- Don't ignore this setting when troubleshooting HTTP-related issues in your Elasticsearch cluster
- Don't assume that increasing this value will always solve header-related problems; investigate root causes first
Frequently Asked Questions
Q: How does http.max_header_size affect Elasticsearch performance?
A: While a larger http.max_header_size allows for more flexibility in request headers, it can potentially impact performance by requiring more memory allocation for header parsing. It's generally best to keep this value as low as possible while still accommodating your application's needs.
Q: Can I set different http.max_header_size values for different nodes in my cluster?
A: Yes, you can set different values for individual nodes using the elasticsearch.yml configuration file. However, it's recommended to keep this setting consistent across all nodes to avoid unexpected behavior.
Q: What happens if a request exceeds the http.max_header_size limit?
A: Elasticsearch will reject the request with a 400 Bad Request error, and the client will need to reduce the size of the headers or split the request into smaller parts.
Q: Is http.max_header_size related to the maximum size of request bodies?
A: No, http.max_header_size only applies to HTTP headers. For controlling the size of request bodies, you should look at other settings like http.max_content_length.
Q: How can I determine if I need to increase the http.max_header_size value?
A: Monitor your Elasticsearch logs for 400 Bad Request errors related to header size. If you see these errors and have verified that the large headers are legitimate and necessary, you may need to consider increasing the value.
