Nagios Core vs OpenNMS Horizon
A side-by-side comparison of two self-hosted monitoring & status options — licensing, setup difficulty, resource needs, and what each one replaces.
| Feature | Nagios Core | OpenNMS Horizon |
|---|---|---|
| Deploy effort | Under-an-hour setup | Under-an-hour setup |
| Health score | 84 · Excellent | 83 · Excellent |
| Category | Monitoring & Status | Monitoring & Status |
| License | GPL-2.0 | AGPL-3.0 |
| Language | C | Java |
| Setup difficulty | Hard | Hard |
| Min. RAM | 512 MB | 4,096 MB |
| Deployment | bare-metal, docker, source | docker, bare-metal |
| GitHub stars | ★ 2,045 | ★ 1,173 |
| First released | 1999 | 2000 |
| Replaces | SolarWinds, PRTG | SolarWinds, PRTG |
What are Nagios Core and OpenNMS Horizon?
Nagios Core
Nagios Core is the open-source monitoring engine that watches hosts, services, and network devices, alerting when problems occur. It is highly extensible through plugins and remains a long-standing standard in IT monitoring.
- Host and service checks
- Massive plugin ecosystem
- Flexible notification rules
- Proven at scale
OpenNMS Horizon
OpenNMS Horizon is an enterprise-grade network monitoring and management platform that handles fault, performance, and traffic monitoring at scale. It supports SNMP, flow analysis, and event correlation.
- Fault and performance monitoring
- Flow analysis
- Event correlation
- Scales to large networks
Nagios Core vs OpenNMS Horizon: key differences
Nagios Core is written in C, while OpenNMS Horizon is built with Java. Licensing differs — GPL-2.0 for Nagios Core versus AGPL-3.0 for OpenNMS Horizon. Nagios Core is the lighter option, starting around 512 MB of RAM against 4,096 MB for OpenNMS Horizon.
Why pick each one
Choose Nagios Core if…
- Battle-tested and stable
- Enormous plugin library
Watch out for
- Configuration is text-file heavy
- Dated web interface
Choose OpenNMS Horizon if…
- Released under the AGPL-3.0 license
- First-class Docker support for quick deployment
- Active community (1.2k GitHub stars)
- Written in Java
Frequently asked questions
Is Nagios Core or OpenNMS Horizon better?
Neither is universally better. Nagios Core has the larger community; both share a hard setup difficulty, so the decision comes down to features and licensing.
Are Nagios Core and OpenNMS Horizon free and open-source?
Yes. Nagios Core is licensed under GPL-2.0 and OpenNMS Horizon under AGPL-3.0. Both can be self-hosted at no software cost.
Can I run Nagios Core and OpenNMS Horizon with Docker?
Nagios Core: yes. OpenNMS Horizon: yes.
Which is lighter on resources, Nagios Core or OpenNMS Horizon?
Nagios Core has the smaller minimum footprint at 512 MB of RAM, compared to about 4,096 MB for OpenNMS Horizon. Real-world usage depends on library size, user count, and enabled features.