module/apmprometheus: prometheus wrapper

Package apmprometheus provides a method for
wrapping a prometheus.Gatherer to adapt it
to the elasticapm.MetricsGatherer interface.
Untyped, Gauge and Counter metric types are
supported; Histogram and and Summary metrics
are silently ignored for now.

module/apmprometheus/gatherer.go

@@ -0,0 +1,67 @@
+package apmprometheus
+
+import (
+	"context"
+
+	"github.com/pkg/errors"
+	"github.com/prometheus/client_golang/prometheus"
+	dto "github.com/prometheus/client_model/go"
+
+	"github.com/elastic/apm-agent-go"
+)
+
+// Wrap returns an elasticapm.MetricsGatherer wrapping g.
+func Wrap(g prometheus.Gatherer) elasticapm.MetricsGatherer {
+	return gatherer{g}
+}
+
+type gatherer struct {
+	p prometheus.Gatherer
+}
+
+// GatherMetrics gathers metrics from the prometheus.Gatherer p.g,
+// and adds them to out.
+func (g gatherer) GatherMetrics(ctx context.Context, out *elasticapm.Metrics) error {
+	metricFamilies, err := g.p.Gather()
+	if err != nil {
+		return errors.WithStack(err)
+	}
+	for _, mf := range metricFamilies {
+		name := mf.GetName()
+		switch mf.GetType() {
+		case dto.MetricType_COUNTER:
+			for _, m := range mf.GetMetric() {
+				v := m.GetCounter().GetValue()
+				out.AddCounter(name, makeLabels(m.GetLabel()), v)
+			}
+		case dto.MetricType_GAUGE:
+			metrics := mf.GetMetric()
+			if name == "go_info" && len(metrics) == 1 && metrics[0].GetGauge().GetValue() == 1 {
+				// Ignore the "go_info" metric from the
+				// built-in GoCollector, as we provide
+				// the same information in the payload.
+				continue
+			}
+			for _, m := range metrics {
+				v := m.GetGauge().GetValue()
+				out.AddGauge(name, makeLabels(m.GetLabel()), v)
+			}
+		case dto.MetricType_UNTYPED:
+			for _, m := range mf.GetMetric() {
+				v := m.GetUntyped().GetValue()
+				out.AddGauge(name, makeLabels(m.GetLabel()), v)
+			}
+		default:
+			// TODO(axw) MetricType_SUMMARY, MetricType_HISTOGRAM
+		}
+	}
+	return nil
+}
+
+func makeLabels(lps []*dto.LabelPair) []elasticapm.MetricLabel {
+	labels := make([]elasticapm.MetricLabel, len(lps))
+	for i, lp := range lps {
+		labels[i] = elasticapm.MetricLabel{Name: lp.GetName(), Value: lp.GetValue()}
+	}
+	return labels
+}

module/apmprometheus/gatherer_test.go

@@ -0,0 +1,99 @@
+package apmprometheus_test
+
+import (
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/elastic/apm-agent-go"
+	"github.com/elastic/apm-agent-go/model"
+	"github.com/elastic/apm-agent-go/module/apmprometheus"
+	"github.com/elastic/apm-agent-go/transport/transporttest"
+)
+
+func TestGoCollector(t *testing.T) {
+	g := apmprometheus.Wrap(prometheus.DefaultGatherer)
+	metrics := gatherMetrics(g)
+	require.Len(t, metrics, 1)
+	assert.Nil(t, metrics[0].Labels)
+
+	assert.Contains(t, metrics[0].Samples, "go_memstats_alloc_bytes")
+	assert.Contains(t, metrics[0].Samples, "go_memstats_alloc_bytes_total")
+	assert.NotNil(t, metrics[0].Samples["go_memstats_alloc_bytes"].Value)
+	assert.NotNil(t, metrics[0].Samples["go_memstats_alloc_bytes_total"].Count)
+}
+
+func TestLabels(t *testing.T) {
+	r := prometheus.NewRegistry()
+	httpReqsTotal := prometheus.NewCounterVec(
+		prometheus.CounterOpts{Name: "http_requests_total", Help: "."},
+		[]string{"code", "method"},
+	)
+	httpReqsInflight := prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{Name: "http_requests_inflight", Help: "."},
+		[]string{"code", "method"},
+	)
+	r.MustRegister(httpReqsTotal)
+	r.MustRegister(httpReqsInflight)
+
+	httpReqsTotal.WithLabelValues("404", "GET").Inc()
+	httpReqsTotal.WithLabelValues("200", "PUT").Inc()
+	httpReqsTotal.WithLabelValues("200", "GET").Add(123)
+	httpReqsInflight.WithLabelValues("200", "GET").Set(10)
+
+	g := apmprometheus.Wrap(r)
+	metrics := gatherMetrics(g)
+
+	assert.Equal(t, []*model.Metrics{{
+		Labels: model.StringMap{
+			{Key: "code", Value: "200"},
+			{Key: "method", Value: "GET"},
+		},
+		Samples: map[string]model.Metric{
+			"http_requests_total": {
+				Count: newFloat64(123),
+			},
+			"http_requests_inflight": {
+				Value: newFloat64(10),
+			},
+		},
+	}, {
+		Labels: model.StringMap{
+			{Key: "code", Value: "200"},
+			{Key: "method", Value: "PUT"},
+		},
+		Samples: map[string]model.Metric{
+			"http_requests_total": {
+				Count: newFloat64(1),
+			},
+		},
+	}, {
+		Labels: model.StringMap{
+			{Key: "code", Value: "404"},
+			{Key: "method", Value: "GET"},
+		},
+		Samples: map[string]model.Metric{
+			"http_requests_total": {
+				Count: newFloat64(1),
+			},
+		},
+	}}, metrics)
+}
+
+func gatherMetrics(g elasticapm.MetricsGatherer) []*model.Metrics {
+	tracer, transport := transporttest.NewRecorderTracer()
+	defer tracer.Close()
+	tracer.AddMetricsGatherer(g)
+	tracer.SendMetrics(nil)
+	metrics := transport.Payloads()[0].Metrics()
+	for _, s := range metrics {
+		s.Timestamp = model.Time{}
+	}
+	return metrics
+}
+
+func newFloat64(v float64) *float64 {
+	return &v
+}