Add example test for the prometheus exporter (#8137)

We used to have the examples in core, but now that they are in contrib it can be hard to find examples of how to use the prometheus exporter. Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>
2026-06-03 18:35:08 +02:00 · 2026-04-08 15:18:24 -04:00
parent edd072f2c9
commit 7ac83c37af
2 changed files with 203 additions and 1 deletions
@@ -0,0 +1,202 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package prometheus_test
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"github.com/prometheus/common/model"
+	"github.com/prometheus/otlptranslator"
+
+	otelprom "go.opentelemetry.io/otel/exporters/prometheus"
+	otelmetric "go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/sdk/metric"
+	semconv "go.opentelemetry.io/otel/semconv/v1.40.0"
+)
+
+func Example() {
+	// Create a new Prometheus exporter. It automatically registers with the DefaultRegisterer.
+	exporter, err := otelprom.New()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Register the exporter with a new MeterProvider.
+	provider := metric.NewMeterProvider(metric.WithReader(exporter))
+	meter := provider.Meter(
+		"example-global",
+		otelmetric.WithInstrumentationVersion("v1.0.0"),
+		otelmetric.WithSchemaURL(semconv.SchemaURL),
+	)
+
+	// Create a counter instrument.
+	counter, err := meter.Float64Counter("bar", otelmetric.WithDescription("a simple counter"))
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	ctx := context.Background()
+	counter.Add(ctx, 10)
+
+	// Serve metrics using promhttp.Handler().
+	// In production, you would use http.ListenAndServe(":8080", promhttp.Handler()).
+	// For this testable example, we use httptest.NewServer.
+	server := httptest.NewServer(promhttp.Handler())
+	defer server.Close()
+
+	// Make an HTTP request to the endpoint.
+	resp, err := http.Get(server.URL) //nolint:noctx
+	if err != nil {
+		panic(err)
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		panic(err)
+	}
+
+	// The response contains all metrics registered with the default registry,
+	// including Go runtime metrics. To make this example testable and deterministic,
+	// we filter the output for lines containing our metric name.
+	lines := strings.SplitSeq(string(body), "\n")
+	for line := range lines {
+		if strings.Contains(line, "bar") {
+			fmt.Println(line)
+		}
+	}
+
+	// Output:
+	// # HELP bar_total a simple counter
+	// # TYPE bar_total counter
+	// bar_total{otel_scope_name="example-global",otel_scope_schema_url="https://opentelemetry.io/schemas/1.40.0",otel_scope_version="v1.0.0"} 10
+}
+
+func Example_customRegistry() {
+	// Create a custom Prometheus registry. This is often used to avoid global state.
+	reg := prometheus.NewRegistry()
+
+	// Create a new Prometheus exporter using the custom registry.
+	exporter, err := otelprom.New(otelprom.WithRegisterer(reg))
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Register the exporter with a new MeterProvider.
+	provider := metric.NewMeterProvider(metric.WithReader(exporter))
+	meter := provider.Meter(
+		"example-custom",
+		otelmetric.WithInstrumentationVersion("v1.0.0"),
+		otelmetric.WithSchemaURL(semconv.SchemaURL),
+	)
+
+	// Create a counter instrument.
+	counter, err := meter.Float64Counter("foo", otelmetric.WithDescription("another counter"))
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	ctx := context.Background()
+	counter.Add(ctx, 5)
+
+	// Serve metrics using promhttp.HandlerFor.
+	server := httptest.NewServer(promhttp.HandlerFor(reg, promhttp.HandlerOpts{}))
+	defer server.Close()
+
+	// Make an HTTP request to the endpoint.
+	resp, err := http.Get(server.URL) //nolint:noctx
+	if err != nil {
+		panic(err)
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		panic(err)
+	}
+
+	// Filter the output for lines containing our metric name.
+	lines := strings.SplitSeq(string(body), "\n")
+	for line := range lines {
+		if strings.Contains(line, "foo") {
+			fmt.Println(line)
+		}
+	}
+
+	// Output:
+	// # HELP foo_total another counter
+	// # TYPE foo_total counter
+	// foo_total{otel_scope_name="example-custom",otel_scope_schema_url="https://opentelemetry.io/schemas/1.40.0",otel_scope_version="v1.0.0"} 5
+}
+
+func Example_noTranslation() {
+	// Set NameEscapingScheme to NoEscaping to prevent the prometheus client from escaping to underscores.
+	model.NameEscapingScheme = model.NoEscaping
+
+	// Create a new Prometheus exporter using NoTranslation strategy.
+	// This keeps the original OpenTelemetry metric names.
+	// It uses the global registry by default.
+	exporter, err := otelprom.New(
+		otelprom.WithTranslationStrategy(otlptranslator.NoTranslation),
+	)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Register the exporter with a new MeterProvider.
+	provider := metric.NewMeterProvider(metric.WithReader(exporter))
+	meter := provider.Meter(
+		"example-no-translation",
+		otelmetric.WithInstrumentationVersion("v1.0.0"),
+		otelmetric.WithSchemaURL(semconv.SchemaURL),
+	)
+
+	// Create a counter instrument.
+	// We use a name with a dot ("my.metric").
+	// With NoTranslation strategy, suffixes like _total are not added.
+	counter, err := meter.Float64Counter("my.metric", otelmetric.WithDescription("a counter without translation"))
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	ctx := context.Background()
+	counter.Add(ctx, 5)
+
+	// Serve metrics using promhttp.Handler (uses default gatherer).
+	server := httptest.NewServer(promhttp.Handler())
+	defer server.Close()
+
+	// Make an HTTP request to the endpoint.
+	resp, err := http.Get(server.URL) //nolint:noctx
+	if err != nil {
+		panic(err)
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		panic(err)
+	}
+
+	// Filter the output for lines containing our metric name.
+	lines := strings.SplitSeq(string(body), "\n")
+	for line := range lines {
+		if strings.Contains(line, "my.metric") {
+			fmt.Println(line)
+		}
+	}
+
+	// Output:
+	// # HELP "my.metric" a counter without translation
+	// # TYPE "my.metric" counter
+	// {"my.metric",otel_scope_name="example-no-translation",otel_scope_schema_url="https://opentelemetry.io/schemas/1.40.0",otel_scope_version="v1.0.0"} 5
+}
@@ -9,6 +9,7 @@ retract v0.59.0
 require (
 	github.com/prometheus/client_golang v1.23.2
 	github.com/prometheus/client_model v0.6.2
+	github.com/prometheus/common v0.67.5
 	github.com/prometheus/otlptranslator v1.0.0
 	github.com/stretchr/testify v1.11.1
 	go.opentelemetry.io/otel v1.43.0
@@ -29,7 +30,6 @@ require (
 	github.com/kylelemons/godebug v1.1.0 // indirect
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
-	github.com/prometheus/common v0.67.5 // indirect
 	github.com/prometheus/procfs v0.20.1 // indirect
 	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
 	go.yaml.in/yaml/v2 v2.4.4 // indirect