feat(otel): add module for our OpenTelemetry SDK wrapper

otel/README.md

@@ -0,0 +1,26 @@
+# How to use
+
+```go
+
+package main
+
+import (
+  "context"
+
+  "github.com/Scalingo/go-utils/otel"
+  "github.com/kelseyhightower/envconfig"
+)
+
+func main() {
+  ctx := context.Background()
+
+  // Initialize Otel
+  err := otel.New(ctx)
+  if err != nil {
+    return
+  }
+
+  // Handle shutdown properly so nothing leaks.
+  defer otel.Shutdown(ctx)
+}
+```

otel/go.mod

@@ -0,0 +1,35 @@
+module github.com/Scalingo/go-utils/otel
+
+go 1.23.4
+
+require (
+	github.com/Scalingo/go-utils/errors/v2 v2.4.0
+	github.com/kelseyhightower/envconfig v1.4.0
+	go.opentelemetry.io/otel v1.34.0
+	go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.34.0
+	go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp v1.34.0
+	go.opentelemetry.io/otel/exporters/stdout/stdoutmetric v1.34.0
+	go.opentelemetry.io/otel/sdk v1.34.0
+	go.opentelemetry.io/otel/sdk/metric v1.34.0
+)
+
+require (
+	github.com/cenkalti/backoff/v4 v4.3.0 // indirect
+	github.com/go-logr/logr v1.4.2 // indirect
+	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/grpc-ecosystem/grpc-gateway/v2 v2.25.1 // indirect
+	github.com/pkg/errors v0.9.1 // indirect
+	go.opentelemetry.io/auto/sdk v1.1.0 // indirect
+	go.opentelemetry.io/otel/metric v1.34.0 // indirect
+	go.opentelemetry.io/otel/trace v1.34.0 // indirect
+	go.opentelemetry.io/proto/otlp v1.5.0 // indirect
+	golang.org/x/net v0.34.0 // indirect
+	golang.org/x/sys v0.29.0 // indirect
+	golang.org/x/text v0.21.0 // indirect
+	google.golang.org/genproto/googleapis/api v0.0.0-20250115164207-1a7da9e5054f // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20250115164207-1a7da9e5054f // indirect
+	google.golang.org/grpc v1.69.4 // indirect
+	google.golang.org/protobuf v1.36.3 // indirect
+	gopkg.in/errgo.v1 v1.0.1 // indirect
+)

otel/go.sum

@@ -0,0 +1,77 @@
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otel/otel.go

@@ -0,0 +1,149 @@
+package otel
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	otelsdk "go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc"
+	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp"
+	"go.opentelemetry.io/otel/exporters/stdout/stdoutmetric"
+	sdkmetric "go.opentelemetry.io/otel/sdk/metric"
+	"go.opentelemetry.io/otel/sdk/resource"
+	semconv "go.opentelemetry.io/otel/semconv/v1.26.0"
+
+	"github.com/kelseyhightower/envconfig"
+
+	"github.com/Scalingo/go-utils/errors/v2"
+)
+
+type Config struct {
+	ServiceName        string        `required:"true" split_words:"true"`
+	Debug              bool          `default:"false"`
+	ExporterType       string        `default:"http" split_words:"true"`
+	CollectionInterval time.Duration `default:"10s" split_words:"true"`
+}
+
+// Providers encapsulates OpenTelemetry providers and utilities
+type Providers struct {
+	meterProvider *sdkmetric.MeterProvider
+	shutdownFunc  func(context.Context) error
+	config        Config
+}
+
+var (
+	globalProviders *Providers
+
+	// once ensures that initialization happens only once.
+	globalOnce sync.Once
+)
+
+// Initializes the Providers as a singleton.
+func New(ctx context.Context) error {
+	var err error
+	globalOnce.Do(func() {
+		// Get Otel configuration from environment
+		var cfg Config
+		err = envconfig.Process("OTEL", &cfg)
+		if err != nil {
+			return
+		}
+		globalProviders, err = setupProviders(ctx, cfg)
+	})
+	return err
+}
+
+func setupProviders(ctx context.Context, cfg Config) (*Providers, error) {
+	var shutdownFuncs []func(context.Context) error
+
+	// shutdown calls cleanup functions registered via shutdownFuncs.
+	// The errors from the calls are joined.
+	// Each registered cleanup will be invoked once.
+	shutdown := func(ctx context.Context) error {
+		var err error
+		for _, fn := range shutdownFuncs {
+			shutdownErr := fn(ctx)
+			if shutdownErr != nil {
+				err = errors.Wrapf(ctx, err, "failed to shutdown provider: %v", shutdownErr)
+			}
+		}
+		shutdownFuncs = nil
+		return err
+	}
+
+	// handleErr calls shutdown for cleanup and makes sure that all errors are returned.
+	handleErr := func(inErr error) error {
+		err := shutdown(ctx)
+		if err != nil {
+			return errors.Wrapf(ctx, inErr, "failed to shutdown otel providers: %v", err)
+		}
+		return inErr
+	}
+
+	// Set up meter provider.
+	meterProvider, err := newMeterProvider(ctx, cfg)
+	if err != nil {
+		return nil, handleErr(err)
+	}
+	shutdownFuncs = append(shutdownFuncs, meterProvider.Shutdown)
+	otelsdk.SetMeterProvider(meterProvider)
+
+	return &Providers{
+		meterProvider: meterProvider,
+		shutdownFunc:  shutdown,
+		config:        cfg,
+	}, nil
+}
+
+func newMeterProvider(ctx context.Context, cfg Config) (*sdkmetric.MeterProvider, error) {
+	if cfg.ServiceName == "" {
+		return nil, errors.New(ctx, "ServiceName is required")
+	}
+	metricsExporter, err := newMetricsExporter(ctx, cfg)
+	if err != nil {
+		return nil, errors.Wrap(ctx, err, "failed to load exporter")
+	}
+	metricsReader := sdkmetric.NewPeriodicReader(metricsExporter, sdkmetric.WithInterval(cfg.CollectionInterval))
+
+	res, err := resource.Merge(
+		resource.Default(),
+		resource.NewWithAttributes(
+			semconv.SchemaURL,
+			semconv.ServiceNameKey.String(cfg.ServiceName),
+		),
+	)
+	if err != nil {
+		return nil, errors.Wrap(ctx, err, "failed to create resource")
+	}
+
+	// Initialize MeterProvider
+	provider := sdkmetric.NewMeterProvider(
+		sdkmetric.WithReader(metricsReader),
+		sdkmetric.WithResource(res),
+	)
+
+	return provider, nil
+}
+
+func newMetricsExporter(ctx context.Context, cfg Config) (sdkmetric.Exporter, error) {
+	if cfg.Debug {
+		return stdoutmetric.New(stdoutmetric.WithPrettyPrint())
+	}
+	switch cfg.ExporterType {
+	case "http":
+		return otlpmetrichttp.New(ctx)
+	case "grpc":
+		return otlpmetricgrpc.New(ctx)
+	default:
+		return nil, errors.New(ctx, "invalid exporter type")
+	}
+}
+
+// Gracefully shuts down the providers
+func Shutdown(ctx context.Context) error {
+	if err := globalProviders.shutdownFunc(ctx); err != nil {
+		return errors.Wrap(ctx, err, "failed to shutdown otel providers")
+	}
+	return nil
+}