Drop the global Tracer instance

Use the preferred otel.GetTracerProvider() idiom and create dedicated
Tracer instances as needed, which seems to be best practice.

ldap/pool.go

@@ -7,10 +7,10 @@ import (
 	"net/url"
 	"time"
 
-	"git.autistici.org/ai3/go-common/tracing"
 	"github.com/cenkalti/backoff/v4"
 	"github.com/go-ldap/ldap/v3"
 	"github.com/prometheus/client_golang/prometheus"
+	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/codes"
 	"go.opentelemetry.io/otel/trace"
@@ -158,14 +158,11 @@ func NewConnectionPool(uri, bindDN, bindPw string, cacheSize int) (*ConnectionPo
 
 func (p *ConnectionPool) doRequest(ctx context.Context, name string, attrs []attribute.KeyValue, fn func(*ldap.Conn) error) error {
 	// Tracing: initialize a new client span.
-	var span trace.Span
-	if tracing.Enabled {
-		ctx, span = tracing.Tracer.Start(ctx, name, trace.WithSpanKind(trace.SpanKindClient))
-		defer span.End()
+	ctx, span := otel.GetTracerProvider().Tracer("ldap").Start(ctx, name, trace.WithSpanKind(trace.SpanKindClient))
+	defer span.End()
 
-		if len(attrs) > 0 {
-			span.SetAttributes(attrs...)
-		}
+	if len(attrs) > 0 {
+		span.SetAttributes(attrs...)
 	}
 
 	rerr := backoff.Retry(func() error {
@@ -269,10 +266,6 @@ func isProtocolError(err error) bool {
 }
 
 func setSpanStatus(span trace.Span, err error) {
-	if span == nil {
-		return
-	}
-
 	switch err {
 	case nil:
 		span.SetStatus(codes.Ok, "OK")

tracing/tracing.go

@@ -19,16 +19,12 @@ import (
 	"go.opentelemetry.io/otel/sdk/resource"
 	"go.opentelemetry.io/otel/sdk/trace"
 	semconv "go.opentelemetry.io/otel/semconv/v1.12.0"
-	apitrace "go.opentelemetry.io/otel/trace"
 )
 
 var (
 	// Enabled reports whether tracing is globally enabled or not.
 	Enabled bool
 
-	// Global Tracer instance.
-	Tracer apitrace.Tracer
-
 	initOnce sync.Once
 )
 
@@ -116,6 +112,9 @@ func initTracing(serviceName string) {
 			return
 		}
 
+		// The sampling policy only applies to incoming requests for
+		// which tracing is not already enabled: in this case, we
+		// always pass-through.
 		var sampler trace.Sampler
 		switch config.Sample {
 		case "", "always":
@@ -132,13 +131,12 @@ func initTracing(serviceName string) {
 		}
 
 		tp := trace.NewTracerProvider(
-			trace.WithSampler(sampler),
+			trace.WithSampler(trace.ParentBased(sampler)),
 			trace.WithBatcher(ze),
 			trace.WithResource(defaultResource(serviceName)),
 		)
 
 		otel.SetTracerProvider(tp)
-		Tracer = tp.Tracer(serviceName)
 
 		otel.SetTextMapPropagator(
 			propagation.NewCompositeTextMapPropagator(
@@ -163,7 +161,7 @@ func Init() {
 // Must call Init() first.
 func WrapTransport(t http.RoundTripper) http.RoundTripper {
 	if Enabled {
-		t = othttp.NewTransport(t, othttp.WithPublicEndpoint())
+		t = othttp.NewTransport(t)
 	}
 	return t
 }
@@ -178,7 +176,10 @@ func WrapHandler(h http.Handler, endpointAddr string) http.Handler {
 	}
 
 	// Format span names with the request URL path.
-	return othttp.NewHandler(h, serviceName, othttp.WithSpanNameFormatter(func(op string, r *http.Request) string {
-		return r.URL.Path
-	}))
+	return othttp.NewHandler(
+		h, serviceName,
+		othttp.WithSpanNameFormatter(func(op string, r *http.Request) string {
+			return r.URL.Path
+		}),
+	)
 }