Configure a NameBased sampler to filter out most of traces

tracing/plugin/otlp.go

@@ -21,6 +21,7 @@ import (
 	"fmt"
 	"io"
 	"net/url"
+	"strings"
 	"time"
 
 	"github.com/containerd/containerd/errdefs"
@@ -101,6 +102,7 @@ type OTLPConfig struct {
 type TraceConfig struct {
 	ServiceName        string  `toml:"service_name"`
 	TraceSamplingRatio float64 `toml:"sampling_ratio"`
+	AllowedNames       string  `toml:"allowed_names"`
 }
 
 type closer struct {
@@ -159,12 +161,23 @@ func newTracer(ctx context.Context, config *TraceConfig, procs []trace.SpanProce
 			// Service name used to displace traces in backends
 			semconv.ServiceNameKey.String(config.ServiceName),
 		),
+		resource.WithFromEnv(),
 	)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create resource: %w", err)
 	}
 
-	sampler := trace.ParentBased(trace.TraceIDRatioBased(config.TraceSamplingRatio))
+	if config.TraceSamplingRatio < 1 && config.AllowedNames == "" {
+		return nil, fmt.Errorf("only one of trace_sampling_ratio or allowed_names can be set")
+	}
+
+	var sampler trace.Sampler
+	if config.AllowedNames == "" {
+		sampler = trace.ParentBased(trace.TraceIDRatioBased(config.TraceSamplingRatio))
+	} else {
+		allowedNames := strings.Split(config.AllowedNames, ",")
+		sampler = trace.ParentBased(NameBased(allowedNames))
+	}
 
 	opts := []trace.TracerProviderOption{
 		trace.WithSampler(sampler),

tracing/plugin/sampler.go

@@ -0,0 +1,46 @@
+package plugin
+
+import (
+	"fmt"
+
+	sdkTrace "go.opentelemetry.io/otel/sdk/trace"
+	"go.opentelemetry.io/otel/trace"
+)
+
+type NameSampler struct {
+	// allow is a set of names that should be sampled.
+	// Uses a map of empty structs for O(1) lookups and no memory overhead.
+	allow map[string]struct{}
+}
+
+// NameBased returns a Sampler that samples every span having a certain name.
+// It should be used in conjunction with the ParentBased sampler so that the child spans are also sampled.
+func NameBased(allowedNames []string) NameSampler {
+	allowedNamesMap := make(map[string]struct{}, len(allowedNames))
+	for _, name := range allowedNames {
+		allowedNamesMap[name] = struct{}{}
+	}
+	return NameSampler{
+		allow: allowedNamesMap,
+	}
+}
+
+func (ns NameSampler) ShouldSample(parameters sdkTrace.SamplingParameters) sdkTrace.SamplingResult {
+	psc := trace.SpanContextFromContext(parameters.ParentContext)
+
+	if _, ok := ns.allow[parameters.Name]; ok {
+		return sdkTrace.SamplingResult{
+			Decision:   sdkTrace.RecordAndSample,
+			Tracestate: psc.TraceState(),
+		}
+	}
+
+	return sdkTrace.SamplingResult{
+		Decision:   sdkTrace.Drop,
+		Tracestate: psc.TraceState(),
+	}
+}
+
+func (ns NameSampler) Description() string {
+	return fmt.Sprintf("NameBased:{%v}", ns.allow)
+}