Threshold Creation

For information on how to create a basic or expression-based threshold, see Set up a threshold in the Quick Start section. This section describes related thresholding tasks.

Use metadata in a threshold

Metadata in expression-based thresholds can streamline threshold creation. The Metadata DSL (domain specific language) lets you use patterns in an expression, whereby the metadata is replaced with a corresponding value during the collection process. A single expression can behave differently based on the node it is tested against.

During evaluation of an expression, the following scopes are available:

Metadata is also supported in value, re-arm, and trigger fields for Single-DS and expression-based thresholds. For more information on metadata and how to define it, see Metadata.

Example

This procedure uses metadata to trigger an event when the number of logged-in users exceeds one.

The expression is in the form `${context:key|context_fallback:key_fallback|…​|default}`. Before using metadata in a threshold, you need to add the metadata context pair—in this case, a requisition key called `userLimit` (see Adding metadata through the web UI). 1. Click the Gear symbol in the top-right of the screen. 2. Under Performance Measurement, click Configure Thresholds. 3. Click Edit beside the `netsnmp` group. 4. Click Create New Expression-based Threshold. 5. Fill in the following information: • Type: High • Expression: `hrSystemNumUsers /${requisition:userLimit|1}`

• Datasource type: Node

• Value: 1

• Rearm: 1

• Description: Too many logged-in users

6. Click Save.

This expression will trigger an event when the number of logged-in users exceeds one.

Confirm that you are collecting metrics

Before creating a threshold, you should make sure you are collecting the metric against which you want to threshold:

1. Choose   Resource Graphs.

2. Select one of the listed resources.

3. Under SNMP Node Data, select   Graph Selection.

4. Scroll to find the graph for the metric you want to threshold.

You can click the Binoculars symbol to display only that graph.

Determine the data source

Creating a threshold requires the name of the data source generating the metrics on which you want to threshold. Data source names for the SNMP protocol appear in `etc/snmp-graph.properties.d`.

To determine the name of the data source, navigate to the Resource Graphs screen:

1. Choose   Resource Graphs.

2. Select one of the listed resources.

3. Under SNMP Node Data, select   Graph Selection.

4. Scroll through the graphs to find the title of the graph that displays the metric on which you want to threshold. For example, "Number of Processes" or "System Uptime":

5. Go to `etc/snmp-graph.properties.d` and search for the title of the graph (for example, "System Uptime").

6. Note the name of the data source, and type it in the Datasource box when you create your threshold.