converts Resource into a target_info metric on the prometheus exporter (#3285)

* converts `Resource` into a `target_info` metric on the prometheus exporter

CHANGELOG.md

@@ -12,6 +12,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Prometheus exporter will register with a prometheus registerer on creation, there are options to control this. (#3239)
 - Added the `WithAggregationSelector` option to the `go.opentelemetry.io/otel/exporters/prometheus` package to change the `AggregationSelector` used. (#3341)
+- Prometheus exporter will convert metrics `Resource` into a `target_info` metric. (#3285)
 
 ### Changed
 

exporters/prometheus/confg_test.go

@@ -20,7 +20,6 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/stretchr/testify/assert"
 
-	"go.opentelemetry.io/otel/sdk/metric"
 	"go.opentelemetry.io/otel/sdk/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/view"
 )
@@ -31,30 +30,34 @@ func TestNewConfig(t *testing.T) {
 	aggregationSelector := func(view.InstrumentKind) aggregation.Aggregation { return nil }
 
 	testCases := []struct {
-		name            string
-		options         []Option
-		wantRegisterer  prometheus.Registerer
-		wantAggregation metric.AggregationSelector
+		name       string
+		options    []Option
+		wantConfig config
 	}{
 		{
-			name:           "Default",
-			options:        nil,
-			wantRegisterer: prometheus.DefaultRegisterer,
+			name:    "Default",
+			options: nil,
+			wantConfig: config{
+				registerer: prometheus.DefaultRegisterer,
+			},
 		},
 		{
 			name: "WithRegisterer",
 			options: []Option{
 				WithRegisterer(registry),
 			},
-			wantRegisterer: registry,
+			wantConfig: config{
+				registerer: registry,
+			},
 		},
 		{
 			name: "WithAggregationSelector",
 			options: []Option{
 				WithAggregationSelector(aggregationSelector),
 			},
-			wantRegisterer:  prometheus.DefaultRegisterer,
-			wantAggregation: aggregationSelector,
+			wantConfig: config{
+				registerer: prometheus.DefaultRegisterer,
+			},
 		},
 		{
 			name: "With Multiple Options",
@@ -62,22 +65,39 @@ func TestNewConfig(t *testing.T) {
 				WithRegisterer(registry),
 				WithAggregationSelector(aggregationSelector),
 			},
-			wantRegisterer:  registry,
-			wantAggregation: aggregationSelector,
+
+			wantConfig: config{
+				registerer: registry,
+			},
 		},
 		{
 			name: "nil options do nothing",
 			options: []Option{
 				WithRegisterer(nil),
 			},
-			wantRegisterer: prometheus.DefaultRegisterer,
+			wantConfig: config{
+				registerer: prometheus.DefaultRegisterer,
+			},
+		},
+		{
+			name: "without target_info metric",
+			options: []Option{
+				WithoutTargetInfo(),
+			},
+			wantConfig: config{
+				registerer:        prometheus.DefaultRegisterer,
+				disableTargetInfo: true,
+			},
 		},
 	}
 	for _, tt := range testCases {
 		t.Run(tt.name, func(t *testing.T) {
 			cfg := newConfig(tt.options...)
 
-			assert.Equal(t, tt.wantRegisterer, cfg.registerer)
+			// tested by TestConfigManualReaderOptions
+			cfg.aggregation = nil
+
+			assert.Equal(t, tt.wantConfig, cfg)
 		})
 	}
 }

exporters/prometheus/config.go

@@ -22,8 +22,9 @@ import (
 
 // config contains options for the exporter.
 type config struct {
-	registerer  prometheus.Registerer
-	aggregation metric.AggregationSelector
+	registerer        prometheus.Registerer
+	disableTargetInfo bool
+	aggregation       metric.AggregationSelector
 }
 
 // newConfig creates a validated config configured with options.
@@ -78,3 +79,13 @@ func WithAggregationSelector(agg metric.AggregationSelector) Option {
 		return cfg
 	})
 }
+
+// WithoutTargetInfo configures the Exporter to not export the resource target_info metric.
+// If not specified, the Exporter will create a target_info metric containing
+// the metrics' resource.Resource attributes.
+func WithoutTargetInfo() Option {
+	return optionFunc(func(cfg config) config {
+		cfg.disableTargetInfo = true
+		return cfg
+	})
+}

exporters/prometheus/exporter.go

@@ -19,6 +19,7 @@ import (
 	"fmt"
 	"sort"
 	"strings"
+	"sync"
 	"unicode"
 	"unicode/utf8"
 
@@ -28,6 +29,12 @@ import (
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/sdk/metric"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
+	"go.opentelemetry.io/otel/sdk/resource"
+)
+
+const (
+	targetInfoMetricName  = "target_info"
+	targetInfoDescription = "Target metadata"
 )
 
 // Exporter is a Prometheus Exporter that embeds the OTel metric.Reader
@@ -41,6 +48,10 @@ var _ metric.Reader = &Exporter{}
 // collector is used to implement prometheus.Collector.
 type collector struct {
 	reader metric.Reader
+
+	disableTargetInfo    bool
+	targetInfo           *metricData
+	createTargetInfoOnce sync.Once
 }
 
 // New returns a Prometheus Exporter.
@@ -53,7 +64,8 @@ func New(opts ...Option) (*Exporter, error) {
 	reader := metric.NewManualReader(cfg.manualReaderOptions()...)
 
 	collector := &collector{
-		reader: reader,
+		reader:            reader,
+		disableTargetInfo: cfg.disableTargetInfo,
 	}
 
 	if err := cfg.registerer.Register(collector); err != nil {
@@ -81,11 +93,12 @@ func (c *collector) Collect(ch chan<- prometheus.Metric) {
 	metrics, err := c.reader.Collect(context.TODO())
 	if err != nil {
 		otel.Handle(err)
+		if err == metric.ErrReaderNotRegistered {
+			return
+		}
 	}
 
-	// TODO(#3166): convert otel resource to target_info
-	// see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/data-model.md#resource-attributes-1
-	for _, metricData := range getMetricData(metrics) {
+	for _, metricData := range c.getMetricData(metrics) {
 		if metricData.valueType == prometheus.UntypedValue {
 			m, err := prometheus.NewConstHistogram(metricData.description, metricData.histogramCount, metricData.histogramSum, metricData.histogramBuckets, metricData.attributeValues...)
 			if err != nil {
@@ -118,8 +131,18 @@ type metricData struct {
 	histogramBuckets map[float64]uint64
 }
 
-func getMetricData(metrics metricdata.ResourceMetrics) []*metricData {
+func (c *collector) getMetricData(metrics metricdata.ResourceMetrics) []*metricData {
 	allMetrics := make([]*metricData, 0)
+
+	c.createTargetInfoOnce.Do(func() {
+		// Resource should be immutable, we don't need to compute again
+		c.targetInfo = c.createInfoMetricData(targetInfoMetricName, targetInfoDescription, metrics.Resource)
+	})
+
+	if c.targetInfo != nil {
+		allMetrics = append(allMetrics, c.targetInfo)
+	}
+
 	for _, scopeMetrics := range metrics.ScopeMetrics {
 		for _, m := range scopeMetrics.Metrics {
 			switch v := m.Data.(type) {
@@ -234,6 +257,23 @@ func getAttrs(attrs attribute.Set) ([]string, []string) {
 	return keys, values
 }
 
+func (c *collector) createInfoMetricData(name, description string, res *resource.Resource) *metricData {
+	if c.disableTargetInfo {
+		return nil
+	}
+
+	keys, values := getAttrs(*res.Set())
+
+	desc := prometheus.NewDesc(name, description, keys, nil)
+	return &metricData{
+		name:            name,
+		description:     desc,
+		attributeValues: values,
+		valueType:       prometheus.GaugeValue,
+		value:           float64(1),
+	}
+}
+
 func sanitizeRune(r rune) rune {
 	if unicode.IsLetter(r) || unicode.IsDigit(r) || r == ':' || r == '_' {
 		return r

exporters/prometheus/exporter_test.go

@@ -29,13 +29,18 @@ import (
 	"go.opentelemetry.io/otel/sdk/metric"
 	"go.opentelemetry.io/otel/sdk/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/view"
+	"go.opentelemetry.io/otel/sdk/resource"
+	semconv "go.opentelemetry.io/otel/semconv/v1.12.0"
 )
 
 func TestPrometheusExporter(t *testing.T) {
 	testCases := []struct {
-		name          string
-		recordMetrics func(ctx context.Context, meter otelmetric.Meter)
-		expectedFile  string
+		name               string
+		emptyResource      bool
+		customResouceAttrs []attribute.KeyValue
+		recordMetrics      func(ctx context.Context, meter otelmetric.Meter)
+		withoutTargetInfo  bool
+		expectedFile       string
 	}{
 		{
 			name:         "counter",
@@ -132,6 +137,63 @@ func TestPrometheusExporter(t *testing.T) {
 				histogram.Record(ctx, 23, attrs...)
 			},
 		},
+		{
+			name:          "empty resource",
+			emptyResource: true,
+			expectedFile:  "testdata/empty_resource.txt",
+			recordMetrics: func(ctx context.Context, meter otelmetric.Meter) {
+				attrs := []attribute.KeyValue{
+					attribute.Key("A").String("B"),
+					attribute.Key("C").String("D"),
+					attribute.Key("E").Bool(true),
+					attribute.Key("F").Int(42),
+				}
+				counter, err := meter.SyncFloat64().Counter("foo", instrument.WithDescription("a simple counter"))
+				require.NoError(t, err)
+				counter.Add(ctx, 5, attrs...)
+				counter.Add(ctx, 10.3, attrs...)
+				counter.Add(ctx, 9, attrs...)
+			},
+		},
+		{
+			name: "custom resource",
+			customResouceAttrs: []attribute.KeyValue{
+				attribute.Key("A").String("B"),
+				attribute.Key("C").String("D"),
+			},
+			expectedFile: "testdata/custom_resource.txt",
+			recordMetrics: func(ctx context.Context, meter otelmetric.Meter) {
+				attrs := []attribute.KeyValue{
+					attribute.Key("A").String("B"),
+					attribute.Key("C").String("D"),
+					attribute.Key("E").Bool(true),
+					attribute.Key("F").Int(42),
+				}
+				counter, err := meter.SyncFloat64().Counter("foo", instrument.WithDescription("a simple counter"))
+				require.NoError(t, err)
+				counter.Add(ctx, 5, attrs...)
+				counter.Add(ctx, 10.3, attrs...)
+				counter.Add(ctx, 9, attrs...)
+			},
+		},
+		{
+			name:              "without target_info",
+			withoutTargetInfo: true,
+			expectedFile:      "testdata/without_target_info.txt",
+			recordMetrics: func(ctx context.Context, meter otelmetric.Meter) {
+				attrs := []attribute.KeyValue{
+					attribute.Key("A").String("B"),
+					attribute.Key("C").String("D"),
+					attribute.Key("E").Bool(true),
+					attribute.Key("F").Int(42),
+				}
+				counter, err := meter.SyncFloat64().Counter("foo", instrument.WithDescription("a simple counter"))
+				require.NoError(t, err)
+				counter.Add(ctx, 5, attrs...)
+				counter.Add(ctx, 10.3, attrs...)
+				counter.Add(ctx, 9, attrs...)
+			},
+		},
 	}
 
 	for _, tc := range testCases {
@@ -139,7 +201,12 @@ func TestPrometheusExporter(t *testing.T) {
 			ctx := context.Background()
 			registry := prometheus.NewRegistry()
 
-			exporter, err := New(WithRegisterer(registry))
+			opts := []Option{WithRegisterer(registry)}
+			if tc.withoutTargetInfo {
+				opts = append(opts, WithoutTargetInfo())
+			}
+
+			exporter, err := New(opts...)
 			require.NoError(t, err)
 
 			customBucketsView, err := view.New(
@@ -152,7 +219,28 @@ func TestPrometheusExporter(t *testing.T) {
 			defaultView, err := view.New(view.MatchInstrumentName("*"))
 			require.NoError(t, err)
 
-			provider := metric.NewMeterProvider(metric.WithReader(exporter, customBucketsView, defaultView))
+			var res *resource.Resource
+
+			if tc.emptyResource {
+				res = resource.Empty()
+			} else {
+				res, err = resource.New(ctx,
+					// always specify service.name because the default depends on the running OS
+					resource.WithAttributes(semconv.ServiceNameKey.String("prometheus_test")),
+					// Overwrite the semconv.TelemetrySDKVersionKey value so we don't need to update every version
+					resource.WithAttributes(semconv.TelemetrySDKVersionKey.String("latest")),
+					resource.WithAttributes(tc.customResouceAttrs...),
+				)
+				require.NoError(t, err)
+
+				res, err = resource.Merge(resource.Default(), res)
+				require.NoError(t, err)
+			}
+
+			provider := metric.NewMeterProvider(
+				metric.WithResource(res),
+				metric.WithReader(exporter, customBucketsView, defaultView),
+			)
 			meter := provider.Meter("testmeter")
 
 			tc.recordMetrics(ctx, meter)

exporters/prometheus/go.mod

@@ -7,6 +7,7 @@ require (
 	github.com/stretchr/testify v1.8.0
 	go.opentelemetry.io/otel v1.11.0
 	go.opentelemetry.io/otel/metric v0.32.3
+	go.opentelemetry.io/otel/sdk v1.11.0
 	go.opentelemetry.io/otel/sdk/metric v0.32.3
 )
 
@@ -22,7 +23,6 @@ require (
 	github.com/prometheus/client_model v0.2.0 // indirect
 	github.com/prometheus/common v0.37.0 // indirect
 	github.com/prometheus/procfs v0.8.0 // indirect
-	go.opentelemetry.io/otel/sdk v1.11.0 // indirect
 	go.opentelemetry.io/otel/trace v1.11.0 // indirect
 	golang.org/x/sys v0.0.0-20220919091848-fb04ddd9f9c8 // indirect
 	google.golang.org/protobuf v1.28.1 // indirect

exporters/prometheus/testdata/counter.txt

@@ -1,3 +1,6 @@
 # HELP foo a simple counter
 # TYPE foo counter
 foo{A="B",C="D",E="true",F="42"} 24.3
+# HELP target_info Target metadata
+# TYPE target_info gauge
+target_info{service_name="prometheus_test",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="latest"} 1

exporters/prometheus/testdata/custom_resource.txt

@@ -0,0 +1,6 @@
+# HELP foo a simple counter
+# TYPE foo counter
+foo{A="B",C="D",E="true",F="42"} 24.3
+# HELP target_info Target metadata
+# TYPE target_info gauge
+target_info{A="B",C="D",service_name="prometheus_test",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="latest"} 1

exporters/prometheus/testdata/empty_resource.txt

@@ -0,0 +1,6 @@
+# HELP foo a simple counter
+# TYPE foo counter
+foo{A="B",C="D",E="true",F="42"} 24.3
+# HELP target_info Target metadata
+# TYPE target_info gauge
+target_info 1

exporters/prometheus/testdata/gauge.txt

@@ -1,3 +1,6 @@
 # HELP bar a fun little gauge
 # TYPE bar gauge
 bar{A="B",C="D"} 75
+# HELP target_info Target metadata
+# TYPE target_info gauge
+target_info{service_name="prometheus_test",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="latest"} 1

exporters/prometheus/testdata/histogram.txt

@@ -13,3 +13,6 @@ histogram_baz_bucket{A="B",C="D",le="1000"} 4
 histogram_baz_bucket{A="B",C="D",le="+Inf"} 4
 histogram_baz_sum{A="B",C="D"} 236
 histogram_baz_count{A="B",C="D"} 4
+# HELP target_info Target metadata
+# TYPE target_info gauge
+target_info{service_name="prometheus_test",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="latest"} 1

exporters/prometheus/testdata/sanitized_labels.txt

@@ -1,3 +1,6 @@
 # HELP foo a sanitary counter
 # TYPE foo counter
 foo{A_B="Q",C_D="Y;Z"} 24.3
+# HELP target_info Target metadata
+# TYPE target_info gauge
+target_info{service_name="prometheus_test",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="latest"} 1

exporters/prometheus/testdata/sanitized_names.txt

@@ -27,3 +27,6 @@ invalid_hist_name_bucket{A="B",C="D",le="10000"} 1
 invalid_hist_name_bucket{A="B",C="D",le="+Inf"} 1
 invalid_hist_name_sum{A="B",C="D"} 23
 invalid_hist_name_count{A="B",C="D"} 1
+# HELP target_info Target metadata
+# TYPE target_info gauge
+target_info{service_name="prometheus_test",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="latest"} 1

exporters/prometheus/testdata/without_target_info.txt

@@ -0,0 +1,3 @@
+# HELP foo a simple counter
+# TYPE foo counter
+foo{A="B",C="D",E="true",F="42"} 24.3