Java-based open-source message broker supported by the Apache community. (See Set Up Message Broker.)


Indicators for problems occurring on entities that Horizon monitors.

Architecture for Learning Enabled Correlation (ALEC)

An OpenNMS framework that uses artificial intelligence and machine learning to provide alarm triage. ALEC groups related alarms so you can better manage the more complex situations they might represent.

Application Perspective Monitoring (APM)

A method that uses the Minion infrastructure to monitor a service’s availability from different perspectives to help identify if nodes are down for everyone or if an outage affects only certain sites. When a service is not responsive an outage will be generated with the corresponding perspective that sees the outage.

Asset data

A set of optional fields, similar to metadata, that can be associated with a node to provide additional information. Examples include physical location and hardware specifications.

Auto-discovered nodes

Nodes that are automatically added to Horizon through routine or one-time discovery. (See Auto-Discovery.)


The percentage of time a node has been detected as being accessible. Horizon typically shows availability statistics for the past 24 hours. This is calculated by subtracting the amount of outage time for a node, interface, or service during the time period.


Microsoft Azure is a cloud hosting platform that allows users to host a variety of services.

Bean Scripting Framework (BSF)

A framework that allows scripting to be used in Java code via a set of Java classes. The Horizon BSF Detector runs arbitrary BSF scripts to determine the existence of a service, and the BSF Monitor uses scripts to determine the status of a service.

Business Service Monitoring (BSM)

A Horizon feature that lets you monitor and generate alerts for issues affecting complex business services spanning multiple nodes.


An open-source distributed/scale-out NoSQL database designed to hold large amounts of structured or unstructured data across many servers. The optional Newts storage strategy requires a Cassandra instance as back-end storage.


User-defined groups of entities on Horizon-monitored networks. They let you define a matrix for aggregating monitoring results. (See Surveillance View.)


A continuous integration and delivery platform that hosts OpenNMS’s CI/CD environment. It integrates with and monitors OpenNMS GitHub repositories, and automatically launches and tests a new build when a commit is detected.


A Horizon sub-service that performs a specific set of tasks.

Direct-discovered nodes

Nodes that are added to Horizon manually through a requisition. (See Directed Discovery.)


An open-source forum platform that hosts OpenNMS’s community forums. There, users can find knowledge base articles, support, announcements, and general discussion about all things OpenNMS.


A process that uses ICMP to find network devices and services in your network and then automatically adds them to monitoring.


An open-source container virtualization service that lets you deploy application-level services without worrying about operating system maintenance. Horizon components may optionally be deployed as Docker containers.


The service on an OpenNMS core that controls the operation of Minions. (See Configuring Minion via Confd.)


A system to manage business rules that supports the Java Rules Engine API standard. It helps provide a more robust infrastructure for workflow and problem state management in the Horizon Alarmd daemon. (See Alarmd daemon.)


A NoSQL database with an integrated search engine based on the Lucene library (see What is NoSQL?). Horizon persists/forwards certain data to Elasticsearch to store flow records and warehouse events and alarm history for long-term storage of this data (see Elasticsearch Integration).


Structured historical records of activities in Horizon and the nodes, interfaces, and services it manages.


Summaries of network traffic sent by network devices.

Foreign source

A data source hosted outside of your local network. To customize monitoring of nodes in a foreign source, you can set a foreign source definition with your desired detectors and policies. (See Foreign Source Definition.)


The actual physical location of a node monitored by Horizon. Nodes can be manually assigned a location, or the location can be automatically determined using the GeoIP Provisioning Adapter.


An open-source analysis and visualization web application. It connects to data sources and generates dashboards with charts, graphs, and alerts. OpenNMS HELM is a Grafana plugin that lets users create customized dashboards with data from Horizon.


An OpenNMS application for creating flexible dashboards to display and customize fault, flow, and performance data from Horizon. HELM works with the Grafana analytics program to customize the data you can view. Not to be confused with the Kubernetes Helm package manager.


An open-source solution from The OpenNMS Group that helps users visualize and monitor everything on their local and remote networks. The free, community-driven project includes the latest technology and features and is delivered through a rapid release cycle.


If This Then That is an automation and workflow service that integrates apps, devices, and services. Horizon can integrate with IFTTT to trigger actions on other services based on customized alarms. (See IFTTT Integration.)


(1) A single, unique occurrence of an element, document, or running program. (2) Used in data collection for storing tabular data as separate data points. (3) Used to refer to the Horizon Core in the OpenNMS Appliance Service UI.

Java Management Extensions (JMX)

A set of tools for managing and monitoring services, resources, and service-oriented networks. Horizon uses it to collect long-term performance data for Java applications. (See JMX Configuration Generator.)


A project management platform that The OpenNMS Group uses to track software issues, feature requests, and IT requests for its projects (including Horizon). (See OpenNMS Jira.)


A clone of RRDTool (see below) written in Java. Default time series database for new Horizon instances.


Clusterable, open-source message broker designed for high-throughput/low-latency event streaming. Originally developed at LinkedIn, it is now supported by the Apache community. (See Set Up Message Broker.)


A component of the Elastic Stack (comprised of Elasticsearch, Logstash, and Kibana). It provides visualization capabilities for data indexed in an Elasticsearch cluster.

KSC reports

Key SNMP customized (KSC) reports provide a way to generate prefabricated graphical views of collected data. They let you display data from different devices and sources (SNMP, ICMP, HTTP) on one page.


An open-source container orchestration system for automating software deployments, scaling, and management. Originally designed by Google, the Cloud Native Computing Foundation now maintains it.


Also referred to as "monitoring location" or "Minion location". Nodes assigned to a monitoring location will be monitored by Minions assigned to the same location. This is distinct from geolocation, which is the actual physical location of the node.

Management Information Base (MIB)

A hardware or software vendor file that describes SNMP objects their products provide. The MIB files can be processed to convert the definition into data collection and event objects for Horizon to work with. Many of the major vendor MIB definitions are included out of the box.


A subscription-based, optimized, and stable version of the OpenNMS Horizon platform that includes only the most stable and secure Horizon features. It is distributed via annual release with monthly security patches.

Message broker

When using Minions and Sentinels, a message broker is required for communication between servers. Horizon has an embedded ActiveMQ server available for smaller deployments. You can swap the broker with a dedicated ActiveMQ, gRPC, or Kafaka cluster to provide scalability and load balancing.


A distributed component that enables OpenNMS to monitor devices and services in locations that OpenNMS cannot reach. Minions communicate with these remote devices while OpenNMS performs coordination and task delegation.


An OpenNMS component that enables horizontal scaling of flow processing. Not required for flow processing, but can improve performance for deployments with a very high volume of flow documents.

Network Operating Center (NOC)

One or more locations where a network is monitored and controlled. (See Network Operations Center.)

New-Fangled Time Series Datastore (Newts)

An OpenNMS time series datastore based on Apache Cassandra. Use it as an alternative persistence strategy instead of JRobin or RRDtool.


An interface responsible for conveying details of Horizon-generated alarms to a higher-level component.


Messages delivered to a set of recipients. Horizon notifications inform users about events in their monitored networks without forcing them to log in and look at the UI.


The ability to measure the internal state of a system by examining its output. If the system’s state can be estimated using only its output, it is considered "observable".

Operator board

Customizable dashboard to visualize monitoring information.


Also known as downtime, this is a period of time that a service is unavailable or offline. It can be caused by systems or communications failures, or planned as part of routine maintenance.

Passive discovery

The process by which a newSuspect event is detected by the Horizon Provisiond service and converted into a new node. Users can configure the Trapd and Syslogd daemons to generate this event when Horizon receives messages from nodes that do not exist in the database. (See Add nodes via newSuspect events.)


Commonly used open-source relational database known for its stability. PostgreSQL scales up but not out. (See Set up PostgreSQL.)

PRovisioning Integration Server (PRIS)

An optional service to gather node inventory information from an external source. Use to generate requisition XML files for creating, updating, or removing nodes for monitoring.


The process of getting your devices, applications, and services into a monitoring system.

Relational Database Management System (RDBMS)

A relational database management system (RDBMS or just RDB) is a common type of database that stores data in tables, with relationships between tables to structure data. Example of such database: PostgreSQL.

Remote Method Invocation (RMI)

Java API that lets one Java Virtual Machine (JVM) running object invoke methods on an object running in another JVM. RMI integration lets you access a remote Horizon and/or Meridian instance for monitoring and management. (See Enabling RMI.)


Sets of nodes to import into Horizon for monitoring and management. You can build requisitions iteratively and import them at a later date. (See Create a Requisition.)


Any hardware or software that Horizon can access.

Round Robin Database (RRD)

A database designed for collection, visualization, and analysis of time-series data. Data is maintained as a fixed-size circular-buffer that overwrites the oldest data with new data.


A small set of data collected from a Horizon-monitored source.


Karaf container that provides scalability for data processing of flow data. It also supports thresholding for streaming telemetry if you are using the Newts time-series strategy.

Simple Mail Transfer Protocol (SMTP)

An internet standard protocol. Horizon monitors SMTP availability on network nodes to ensure that email messages can be sent and received. (See MailTransportMonitor.)

Simple Network Management Protocol (SNMP)

An internet standard protocol used to collect, organize, and modify information about managed devices on an IP network. (See Configure SNMP for Provisioning.)


Self-contained software packages that run in a sandbox and have mediated access to host systems. Our Appliance Service uses snaps to distribute operating system packages and Minion service updates.


The process of automatically recording and transmitting data from an external source to a system in a different location for monitoring or analysis. The Telemetry daemon in Horizon accepts data sent from nodes in one of the supported protocol formats.

Time series, time-series database (TSDB)

Time series is a sequence of data points that occur in successive order over a period of time. A time series database (TSDB) is designed to store and serve time series data. (See Time Series Storage and Time Series Database.)


A description of a network’s elements (devices, services) and the connections among them.


Event triggers generated by SNMP-capable devices on the network and sent to the Horizon Trapd service daemon.

Unique Event Identifier (UEI)

A String that uniquely identifies an event’s type. UEIs must begin with uei.. (See Events and UEIs.)