collector collisions

[acpana]

Overview

IIUC these lines https://github.com/armon/go-metrics/blob/master/prometheus/prometheus.go#L129-L134 will create a collision for the Collector type if we attempt to register more than one PrometheusSink.

Repro

One repro scenario is described here hashicorp/consul#11273 .

Also, I have a test can repro this and will comment below

Proposed Fixes

• IMO, the way we implement .Describe() needs to be reworked

[acpana]

Test to repro:

• two different sinks
• errs out with err = duplicate metrics collector registration attempted

func TestNewPrometheusSink(t *testing.T) {

	gaugeDef := GaugeDefinition{
		Name: []string{"my", "test", "gauge"},
		Help: "A gauge for testing? How helpful!",
	}
	// PrometheusSink config w/ definitions for each metric type
	cfg := PrometheusOpts{
		Expiration:         5 * time.Second,
		GaugeDefinitions:   append([]GaugeDefinition{}, gaugeDef),
		SummaryDefinitions: append([]SummaryDefinition{}),
		CounterDefinitions: append([]CounterDefinition{}),
	}

	sink1, err := NewPrometheusSinkFrom(cfg)

	reg := prometheus.DefaultRegisterer

	if err != nil {
		t.Fatalf("err = %v, want nil", err)
	}

	gaugeDef2 := GaugeDefinition{
		Name: []string{"my2", "test", "gauge"},
		Help: "A gauge for testing? How helpful!",
	}

	cfg2 := PrometheusOpts{
		Expiration:         15 * time.Second,
		GaugeDefinitions:   append([]GaugeDefinition{}, gaugeDef2),
		SummaryDefinitions: append([]SummaryDefinition{}),
		CounterDefinitions: append([]CounterDefinition{}),
	}

	sink2, err := NewPrometheusSinkFrom(cfg2) // errors out
        ...
}