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 wasn't able to use @panser solution 'cause I'm using gauges with labels. My solution involved the creation of com.google.common.util.concurrent.AtomicDouble cache with io.micrometer.core.instrument.Tag's key and values as map key, heres goes:

    private static final Map GAUGE_CACHE = new HashMap<>();

    public void handleGauge(String name, List tags, double value) {
        String gaugeKey = this.gaugeKey(name, tags);
        if (!GAUGE_CACHE.containsKey(gaugeKey)) {
            GAUGE_CACHE.put(gaugeKey, new AtomicDouble());
        }
        Objects.requireNonNull(this.registry.gauge(name, tags, GAUGE_CACHE.get(gaugeKey))).set(value);
    }

    private String gaugeKey(String name, List tags) {
        return name + ":" + tags.stream().map(tag -> tag.getKey() + tag.getValue()).collect(Collectors.joining(""));
    }

That worked pretty well for my needs, hopefully help other people.