Micrometer - Prometheus Gauge displays NaN

Question

I am trying to generate Prometheus metrics with using Micrometer.io with Spring Boot 2.0.0.RELEASE.

When I am trying to expose the size of a List as Gauge, it ke

Answer 1

I had the same issue with Micrometer.io gauges when I used your method #1 meterRegistry.gauge("myGauge", new AtomicDouble()). I am using Scala by the way. I noticed that after I created about 50 gauges, the new gauges after that displayed NaN.

Instead I used:

val atomicDouble = new AtomicDouble()
Gauge
  .builder("myGauge", atomicDouble, new AtomicDoubleToDoubleFunction)
  .strongReference(true)
  .register(meterRegistry)

with

class AtomicDoubleToDoubleFunction extends ToDoubleFunction[AtomicDouble] {
  override def applyAsDouble(value: AtomicDouble): Double = value.doubleValue()
}

This fixed the NaN issue, and all of my gauges appear correctly. I found the .strongReference(true) example from https://www.codota.com/code/java/classes/io.micrometer.core.instrument.Gauge .