Thresholding Tasks

For information on how to create a basic or expression-based threshold, see Step 5: 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 that it is tested against.

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

  • Node metadata

  • Interface metadata

  • Service metadata

Metadata is also supported in the 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).

Follow these steps to create the expression-based threshold:

  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

      Page displaying configuration settings for an example expression-based threshold
      Figure 1. Example expression-based threshold configuration

  6. Click Save.

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

Meridian dashboard displaying events triggered by a threshold
Figure 2. Meridian dashboard displaying threshold-generated events

Confirm that you are collecting metrics

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

  1. Choose Reports  Resource Graphs.

  2. Select one of the listed resources.

  3. Under SNMP Node Data, select Node-Level Performance Data  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 Reports  Resource Graphs.

  2. Select one of the listed resources.

  3. Under SNMP Node Data, select Node-Level Performance Data  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":

    Two example performance data metric graphs: one displays system uptime, and one displays the number of active processes over time
    Figure 3. Meridian performance data metric graphs

  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.