Breaking OpenNMS metric collection with SNMP

2026-09-09 15 min read Monitoring OpenNMS Ronny Trommer

The most common question I get about OpenNMS at scale is some version of this: I have a lot of network equipment, I want SNMP performance data from all of it, how big does the box need to be? The honest answer used to be “it depends”, followed by a shrug about agent behavior.

What I reached for in those situations was the instrumentation log reader. It tells you two things about a running system: how long it takes to collect metrics from your agents, and how long it takes to persist them. The node inventory matters just as much. It tells you the node-to-interface ratio and how the metric collection is composed in your environment.

Reversing the dial: the many faces of gNMI dial-out

Ask five vendors how they do “gNMI dial-out” and you’ll get five different answers. You’ll find everything a custom gRPC service here, an opaque protobuf envelope there, a generic tunnel over on the standards track. When I started to work on gNMI dial-out in nl6, I wanted the whole map, not just the one corner I’d already implemented. The work with the nl6 simulator forces me to understand the landscape.

The punchline up front, because it reframes everything: gNMI has no dial-out.