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Triggers

Triggers are composed of user-defined code that automatically runs on system events through the ExtraHop Trigger API. You can write a trigger, which is a block of JavaScript, through the trigger API to extract, store, and visualize custom wire data events and metrics that are specific to your business, infrastructure, network, clients, and business applications.

Some of the most common workflows that you can perform through triggers include the following operations:

  • Create an application container in which metrics are collected for specific devices. Application containers augment the device-based views that the ExtraHop system constructs by default.
  • Create custom metrics and save them to the ExtraHop datastore. For example, user agent data generated by an HTTP request is not a metric built into the ExtraHop system. However, the ExtraHop Trigger API provides a user agent HTTP property, which enables you to write a trigger that collects user agent data as a custom metric.
  • Generate records and write them to a datastore for long-term storage and retrieval.
  • Send data to syslog consumers, such as Splunk, or to third party databases, such as MongoDB or Kafka, through an open data stream.
  • Perform universal payload analysis (UPA) to access and parse TCP and UDP payloads from unsupported protocols.
  • Initiate packet captures to record individual flows based on user-specified criteria. Your ExtraHop system must be licensed for packet capture to access this feature.

To view all triggers, click the System Settings icon and then click Triggers. From the Triggers page, you can create a trigger or select the checkmark next to a trigger to edit the trigger configuration or modify the trigger script.

Plan a trigger

Writing a trigger to collect custom metrics is a powerful way to monitor your application and network performance. However, triggers consume system resources and can affect system performance, and a poorly-written trigger can cause unnecessary system load. Before you build a trigger, evaluate what you want your trigger to accomplish, identify which events and devices are needed to extract the data you need, and determine whether a solution already exists.

  • Identify the specific information you need to collect, by asking the following types of questions:
    • When will my SSL certificates expire?
    • Is my network getting connections on non-authorized ports?
    • How many slow transactions is my network experiencing?
    • What data do I want to send to Splunk through an open data stream?
  • Review the Metric Catalog to determine whether a built-in metric already exists that extracts the data you need. Built-in metrics do not create additional load on the system.
  • Identify which system events produce the data that you want to collect. For example, a trigger that monitors cloud application activity in your environment might run on HTTP responses and on the open and close of SSL connections. For a complete list of system events, see the ExtraHop Trigger API Reference.
  • Familiarize yourself with the API methods and properties available in the ExtraHop Trigger API Reference. For example, before you get too far in planning your trigger, check the reference to make sure that the property you want to extract is available, or to find out what properties are collected in a default CIFS record.
  • Determine how you want to visualize or store data collected by the trigger. For example, you can view metrics on a dashboard or by protocol, you can send records to the recordstore.
  • Determine if a trigger already exists that meets your needs or might be easily modified; always start with a pre-existing trigger whenever possible. Search the following resources for an existing trigger:

Building triggers

If you determine that you need to build a new trigger, familiarize yourself with the following tasks that must be completed:

  • Configure the trigger to provide details such as the trigger name and whether debugging is enabled. Most importantly, specify which system events the trigger will run on. For example, if you want your trigger to run each time an SSH connection is opened, you will specify SSH_OPEN as the trigger event.
  • Write the trigger script, which specifies the instructions the trigger will carry out when a system event configured for the trigger occurs. The trigger script can provide instructions for a simple task such as creating a custom device count metric called "slow_rsp" or a more complex effort such as monitoring and collecting statistics about the cloud applications accessed in your environment.

After the trigger is complete and running, it is important to check that the trigger is performing as expected.

The Triggers page contains a list of current triggers with the following information:

Name
The user-defined name of the trigger.
Author
The name of the user who wrote the trigger. Default triggers display ExtraHop for this field.
Description
The user-defined description of the trigger.
Assignments
The devices or device groups the trigger is assigned to.
Status
Whether the trigger is enabled. If the trigger is enabled, the number of device assignments also displays.
Debug Log
Whether debugging is enabled. If debugging is enabled, output from debug statements in the trigger script are logged in the debug log output.
Events
The system events that cause the trigger to run, such as HTTP_RESPONSE.
Modified
The last time that the trigger was modified.
Last modified 2023-11-07