Unable to add metric attributes using otelhttp.WithMetricAttributesFn for http server #6540
Open
Description
Description
Unable to add metric attributes using otelhttp.WithMetricAttributesFn for http server. The attributes defined in the function are not included in the produced metrics.
Environment
- OS: macos
- Architecture: arm64
- Go Version: go1.23.4 darwin/arm64
otelhttp: v0.58.0
Steps To Reproduce
- Using this code ...
package main
import (
"context"
"github.com/go-logr/stdr"
"github.com/gorilla/mux"
"github.com/prometheus/client_golang/prometheus/promhttp"
"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
"go.opentelemetry.io/otel"
"go.opentelemetry.io/otel/attribute"
"go.opentelemetry.io/otel/exporters/otlp/otlptrace"
"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
"go.opentelemetry.io/otel/exporters/prometheus"
"go.opentelemetry.io/otel/propagation"
"go.opentelemetry.io/otel/sdk/metric"
"go.opentelemetry.io/otel/sdk/resource"
"go.opentelemetry.io/otel/sdk/trace"
semconv "go.opentelemetry.io/otel/semconv/v1.27.0"
t2 "go.opentelemetry.io/otel/trace"
"log"
"net/http"
"os"
)
func TraceProvider() (tp t2.TracerProvider, meterProvider *metric.MeterProvider) {
appName := os.Getenv("SERVICE_NAME")
ctx := context.Background()
res, err := resource.New(ctx,
resource.WithFromEnv(),
resource.WithProcess(),
resource.WithTelemetrySDK(),
resource.WithHost(),
resource.WithAttributes(
semconv.ServiceNameKey.String(appName),
attribute.String("environment", "TEST"),
),
)
promReader, err := prometheus.New()
meterProvider = metric.NewMeterProvider(
metric.WithResource(res),
metric.WithReader(promReader),
)
sampler := trace.ParentBased(
// TODO: remove this line
trace.AlwaysSample(),
//trace.TraceIDRatioBased(traceConfig.TraceSamplerRatio),
)
exporter, err := otlptrace.New(
context.Background(),
otlptracegrpc.NewClient(),
)
if err != nil {
log.Fatal(err)
}
tp = trace.NewTracerProvider(
trace.WithSampler(sampler),
trace.WithBatcher(exporter),
trace.WithResource(res),
)
otel.SetMeterProvider(meterProvider)
otel.SetTracerProvider(tp)
// TODO: remove this line
otel.SetLogger(stdr.New(log.New(os.Stdout, "", log.LstdFlags|log.Lshortfile)))
otel.SetTextMapPropagator(propagation.NewCompositeTextMapPropagator(propagation.TraceContext{}, propagation.Baggage{}))
return
}
func main() {
// initialize the trace/metric provider
tp, mp := TraceProvider()
// create a new router
router := mux.NewRouter()
// register the health handler
router.HandleFunc("/health", func(w http.ResponseWriter, _ *http.Request) {
w.Header().Set("Content-Type", "application/json")
w.WriteHeader(http.StatusOK)
_, _ = w.Write([]byte("OK"))
}).Methods(http.MethodGet)
// register the metrics handler
router.HandleFunc("/metrics", func(w http.ResponseWriter, r *http.Request) {
promhttp.Handler().ServeHTTP(w, r)
}).Methods(http.MethodGet)
h := otelhttp.NewHandler(
router,
"",
otelhttp.WithTracerProvider(tp),
otelhttp.WithMeterProvider(mp),
otelhttp.WithMetricAttributesFn(
func(r *http.Request) []attribute.KeyValue {
return []attribute.KeyValue{
attribute.String("http.method", r.Method),
attribute.String("http.route", r.URL.Path),
}
},
),
)
srv := &http.Server{
Handler: h,
Addr: ":8081",
}
log.Println("Listening on http://localhost:8081")
err := srv.ListenAndServe()
if err != nil {
log.Fatal(err)
}
}- Run ...
go run main.go
curl "localhost:8081/health"
curl "localhost:8081/metrics"- Observe the metrics output.
Actual Behavior:
The produced metrics do not include the attributes defined inWithMetricAttributesFn
...
http_server_duration_milliseconds_bucket{http_method="GET",http_scheme="http",http_status_code="200",net_host_name="localhost",net_host_port="8081",net_protocol_name="http",net_protocol_version="1.1",otel_scope_name="go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp",otel_scope_version="0.58.0",le="5000"}Expected behavior
expected the produced metrics to include the attribute added in the WithMetricAttributesFn method.
eg.
...
http_server_duration_milliseconds_bucket{http_method="GET",http_scheme="http",http_status_code="200",net_host_name="localhost",net_host_port="8081",net_protocol_name="http",net_protocol_version="1.1",otel_scope_name="go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp",otel_scope_version="0.58.0",le="5000",http.route="/health"}
Additonal Context
I came across #5876 , which added support for custom attributes but it seems to only handle outbound HTTP requests through Transport struct. It looks like this behavior has not been extended to server-side metrics via semconv.HTTPServer .
Proposal and Contribution Inquiry:
Would it make sense to extend this support for HTTP server metrics, possibly in semconv.HTTPServer or a related component?
I’d be happy to contribute a PR if the maintainers are open to this improvement. Please let me know if this is something worth pursuing!