Admission control settings

OpenSearch provides admission control settings to help prevent cluster overload by limiting resource usage for different types of operations. Admission control monitors CPU and I/O usage and can reject requests when resource utilization exceeds configured thresholds.

To learn more about static and dynamic settings, see Configuring OpenSearch.

Transport layer settings

OpenSearch supports the following transport layer admission control settings:

• admission_control.transport.mode (Dynamic, string): Controls the overall admission control mode for the transport layer. Valid values are:
  • disabled (default): Admission control is disabled.
  • shadow: Admission control runs in monitoring mode only, collecting metrics without rejecting requests.
  • enforced: Admission control actively rejects requests when thresholds are exceeded.

CPU-based admission control settings

CPU-based admission control monitors CPU usage and applies limits to different types of operations. All CPU limits are specified as percentages (0–100).

OpenSearch supports the following dynamic CPU-based admission control settings:

• admission_control.cluster.admin.cpu_usage.limit (Dynamic, long): The CPU usage threshold for cluster administration operations. When CPU usage exceeds this limit, cluster admin requests may be rejected to preserve cluster stability. Default is 95.

• admission_control.search.cpu_usage.limit (Dynamic, long): The CPU usage threshold for search operations. When CPU usage exceeds this limit, new search requests may be rejected to prevent cluster overload. Default is 95.

• admission_control.indexing.cpu_usage.limit (Dynamic, long): The CPU usage threshold for indexing operations. When CPU usage exceeds this limit, indexing requests may be rejected to maintain cluster performance. Default is 95.

• admission_control.transport.cpu_usage.mode_override (Dynamic, string): Overrides the global transport mode specifically for CPU-based admission control. Accepts the same values as admission_control.transport.mode: disabled, shadow, or enforced. If not specified, uses the global transport mode setting.

I/O-based admission control settings

I/O-based admission control monitors disk I/O usage and applies limits to different types of operations. All I/O limits are specified as percentages (0–100).

OpenSearch supports the following I/O-based admission control settings:

• admission_control.search.io_usage.limit (Dynamic, long): The I/O usage threshold for search operations. When I/O usage exceeds this limit, search requests may be rejected. Default is 95.

• admission_control.indexing.io_usage.limit (Dynamic, long): The I/O usage threshold for indexing operations. When I/O usage exceeds this limit, indexing requests may be rejected. Default is 95.

• admission_control.cluster_admin.io_usage.limit (Static, long): The I/O usage threshold for cluster administration operations. This is a static setting that requires a cluster restart to modify. Default is 100.

• admission_control.transport.io_usage.mode_override (Dynamic, string): Overrides the global transport mode specifically for I/O-based admission control. Accepts the same values as admission_control.transport.mode: disabled, shadow, or enforced. If not specified, uses the global transport mode setting.