[3.5] Backport add sampling rate to fix distributed tracing

server/embed/config.go

@@ -365,6 +365,9 @@ type Config struct {
 	// that exist at the same time.
 	// Can only be used if ExperimentalEnableDistributedTracing is true.
 	ExperimentalDistributedTracingServiceInstanceID string `json:"experimental-distributed-tracing-instance-id"`
+	// ExperimentalDistributedTracingSamplingRatePerMillion is the number of samples to collect per million spans.
+	// Defaults to 0.
+	ExperimentalDistributedTracingSamplingRatePerMillion int `json:"experimental-distributed-tracing-sampling-rate"`
 
 	// Logger is logger options: currently only supports "zap".
 	// "capnslog" is removed in v3.5.
@@ -758,6 +761,13 @@ func (cfg *Config) Validate() error {
 		return fmt.Errorf("cipher suites cannot be configured when only TLS1.3 is enabled")
 	}
 
+	// Validate distributed tracing configuration but only if enabled.
+	if cfg.ExperimentalEnableDistributedTracing {
+		if err := validateTracingConfig(cfg.ExperimentalDistributedTracingSamplingRatePerMillion); err != nil {
+			return fmt.Errorf("distributed tracing configurition is not valid: (%v)", err)
+		}
+	}
+
 	return nil
 }
 

server/embed/config_tracing.go

@@ -16,6 +16,7 @@ package embed
 
 import (
 	"context"
+	"fmt"
 
 	"go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc"
 	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
@@ -26,13 +27,32 @@ import (
 	"go.uber.org/zap"
 )
 
-func setupTracingExporter(ctx context.Context, cfg *Config) (exporter tracesdk.SpanExporter, options []otelgrpc.Option, err error) {
-	exporter, err = otlptracegrpc.New(ctx,
+const maxSamplingRatePerMillion = 1000000
+
+func validateTracingConfig(samplingRate int) error {
+	if samplingRate < 0 {
+		return fmt.Errorf("tracing sampling rate must be positive")
+	}
+	if samplingRate > maxSamplingRatePerMillion {
+		return fmt.Errorf("tracing sampling rate must be less than %d", maxSamplingRatePerMillion)
+	}
+
+	return nil
+}
+
+type tracingExporter struct {
+	exporter tracesdk.SpanExporter
+	opts     []otelgrpc.Option
+	provider *tracesdk.TracerProvider
+}
+
+func newTracingExporter(ctx context.Context, cfg *Config) (*tracingExporter, error) {
+	exporter, err := otlptracegrpc.New(ctx,
 		otlptracegrpc.WithInsecure(),
 		otlptracegrpc.WithEndpoint(cfg.ExperimentalDistributedTracingAddress),
 	)
 	if err != nil {
-		return nil, nil, err
+		return nil, err
 	}
 
 	res, err := resource.New(ctx,
@@ -41,33 +61,37 @@ func setupTracingExporter(ctx context.Context, cfg *Config) (exporter tracesdk.S
 		),
 	)
 	if err != nil {
-		return nil, nil, err
+		return nil, err
 	}
 
 	if resWithIDKey := determineResourceWithIDKey(cfg.ExperimentalDistributedTracingServiceInstanceID); resWithIDKey != nil {
 		// Merge resources into a new
 		// resource in case of duplicates.
 		res, err = resource.Merge(res, resWithIDKey)
 		if err != nil {
-			return nil, nil, err
+			return nil, err
 		}
 	}
 
-	options = append(options,
+		traceProvider := tracesdk.NewTracerProvider(
+		tracesdk.WithBatcher(exporter),
+		tracesdk.WithResource(res),
+		tracesdk.WithSampler(
+			tracesdk.ParentBased(determineSampler(cfg.ExperimentalDistributedTracingSamplingRatePerMillion)),
+		),
+	)
+
+	options := []otelgrpc.Option{
 		otelgrpc.WithPropagators(
 			propagation.NewCompositeTextMapPropagator(
 				propagation.TraceContext{},
 				propagation.Baggage{},
 			),
 		),
 		otelgrpc.WithTracerProvider(
-			tracesdk.NewTracerProvider(
-				tracesdk.WithBatcher(exporter),
-				tracesdk.WithResource(res),
-				tracesdk.WithSampler(tracesdk.ParentBased(tracesdk.NeverSample())),
-			),
+			traceProvider,
 		),
-	)
+	}
 
 	cfg.logger.Debug(
 		"distributed tracing enabled",
@@ -76,7 +100,29 @@ func setupTracingExporter(ctx context.Context, cfg *Config) (exporter tracesdk.S
 		zap.String("service-instance-id", cfg.ExperimentalDistributedTracingServiceInstanceID),
 	)
 
-	return exporter, options, err
+	return &tracingExporter{
+		exporter: exporter,
+		opts:     options,
+		provider: traceProvider,
+	}, nil
+}
+
+func (te *tracingExporter) Close(ctx context.Context) {
+	if te.provider != nil {
+		te.provider.Shutdown(ctx)
+	}
+
+	if te.exporter != nil {
+		te.exporter.Shutdown(ctx)
+	}
+}
+
+func determineSampler(samplingRate int) tracesdk.Sampler {
+	sampler := tracesdk.NeverSample()
+	if samplingRate == 0 {
+		return sampler
+	}
+	return tracesdk.TraceIDRatioBased(float64(samplingRate) / float64(maxSamplingRatePerMillion))
 }
 
 // As Tracing service Instance ID must be unique, it should

server/embed/config_tracing_test.go

@@ -0,0 +1,83 @@
+// Copyright 2021 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package embed
+
+import (
+	"testing"
+)
+
+const neverSampleDescription = "AlwaysOffSampler"
+
+func TestDetermineSampler(t *testing.T) {
+	tests := []struct {
+		name                   string
+		sampleRate             int
+		wantSamplerDescription string
+	}{
+		{
+			name:                   "sample rate is disabled",
+			sampleRate:             0,
+			wantSamplerDescription: neverSampleDescription,
+		},
+		{
+			name:                   "sample rate is 100",
+			sampleRate:             100,
+			wantSamplerDescription: "TraceIDRatioBased{0.0001}",
+		},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			sampler := determineSampler(tc.sampleRate)
+			if tc.wantSamplerDescription != sampler.Description() {
+				t.Errorf("tracing sampler was not as expected; expected sampler: %#+v, got sampler: %#+v", tc.wantSamplerDescription, sampler.Description())
+			}
+		})
+	}
+}
+
+func TestTracingConfig(t *testing.T) {
+	tests := []struct {
+		name       string
+		sampleRate int
+		wantErr    bool
+	}{
+		{
+			name:       "invalid - sample rate is less than 0",
+			sampleRate: -1,
+			wantErr:    true,
+		},
+		{
+			name:       "invalid - sample rate is more than allowed value",
+			sampleRate: maxSamplingRatePerMillion + 1,
+			wantErr:    true,
+		},
+		{
+			name:       "valid - sample rate is 100",
+			sampleRate: 100,
+			wantErr:    false,
+		},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			err := validateTracingConfig(tc.sampleRate)
+			if err == nil && tc.wantErr {
+				t.Errorf("expected error got (%v) error", err)
+			}
+			if err != nil && !tc.wantErr {
+				t.Errorf("expected no errors, got error: (%v)", err)
+			}
+		})
+	}
+}

server/embed/etcd.go

@@ -228,15 +228,14 @@ func StartEtcd(inCfg *Config) (e *Etcd, err error) {
 
 	if srvcfg.ExperimentalEnableDistributedTracing {
 		tctx := context.Background()
-		tracingExporter, opts, err := setupTracingExporter(tctx, cfg)
+		tracingExporter, err := newTracingExporter(tctx, cfg)
 		if err != nil {
 			return e, err
 		}
-		if tracingExporter == nil || len(opts) == 0 {
-			return e, fmt.Errorf("error setting up distributed tracing")
+		e.tracingExporterShutdown = func() {
+			tracingExporter.Close(tctx)
 		}
-		e.tracingExporterShutdown = func() { tracingExporter.Shutdown(tctx) }
-		srvcfg.ExperimentalTracerOptions = opts
+		srvcfg.ExperimentalTracerOptions = tracingExporter.opts
 
 		e.cfg.logger.Info("distributed tracing setup enabled")
 	}

server/etcdmain/config.go

@@ -276,6 +276,7 @@ func newConfig() *config {
 	fs.StringVar(&cfg.ec.ExperimentalDistributedTracingAddress, "experimental-distributed-tracing-address", embed.ExperimentalDistributedTracingAddress, "Address for distributed tracing used for OpenTelemetry Tracing (if enabled with experimental-enable-distributed-tracing flag).")
 	fs.StringVar(&cfg.ec.ExperimentalDistributedTracingServiceName, "experimental-distributed-tracing-service-name", embed.ExperimentalDistributedTracingServiceName, "Configures service name for distributed tracing to be used to define service name for OpenTelemetry Tracing (if enabled with experimental-enable-distributed-tracing flag). 'etcd' is the default service name. Use the same service name for all instances of etcd.")
 	fs.StringVar(&cfg.ec.ExperimentalDistributedTracingServiceInstanceID, "experimental-distributed-tracing-instance-id", "", "Configures service instance ID for distributed tracing to be used to define service instance ID key for OpenTelemetry Tracing (if enabled with experimental-enable-distributed-tracing flag). There is no default value set. This ID must be unique per etcd instance.")
+	fs.IntVar(&cfg.ec.ExperimentalDistributedTracingSamplingRatePerMillion, "experimental-distributed-tracing-sampling-rate", 0, "Number of samples to collect per million spans for OpenTelemetry Tracing (if enabled with experimental-enable-distributed-tracing flag).")
 
 	// auth
 	fs.StringVar(&cfg.ec.AuthToken, "auth-token", cfg.ec.AuthToken, "Specify auth token specific options.")

server/etcdmain/help.go

@@ -219,6 +219,8 @@ Experimental distributed tracing:
     Distributed tracing service name, must be same across all etcd instances.
   --experimental-distributed-tracing-instance-id ''
     Distributed tracing instance ID, must be unique per each etcd instance.
+  --experimental-distributed-tracing-sampling-rate '0'
+    Number of samples to collect per million spans for distributed tracing. Disabled by default.
 
 v2 Proxy (to be deprecated in v3.6):
   --proxy 'off'

tests/go.mod

@@ -36,6 +36,11 @@ require (
 	go.etcd.io/etcd/pkg/v3 v3.5.10
 	go.etcd.io/etcd/raft/v3 v3.5.10
 	go.etcd.io/etcd/server/v3 v3.5.10
+	go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.46.0
+	go.opentelemetry.io/otel v1.20.0
+	go.opentelemetry.io/otel/sdk v1.20.0
+	go.opentelemetry.io/otel/trace v1.20.0
+	go.opentelemetry.io/proto/otlp v1.0.0
 	go.uber.org/zap v1.17.0
 	golang.org/x/crypto v0.14.0
 	golang.org/x/sync v0.3.0
@@ -72,14 +77,9 @@ require (
 	github.com/tmc/grpc-websocket-proxy v0.0.0-20201229170055-e5319fda7802 // indirect
 	github.com/xiang90/probing v0.0.0-20190116061207-43a291ad63a2 // indirect
 	go.etcd.io/bbolt v1.3.8 // indirect
-	go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.46.0 // indirect
-	go.opentelemetry.io/otel v1.20.0 // indirect
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.20.0 // indirect
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.20.0 // indirect
 	go.opentelemetry.io/otel/metric v1.20.0 // indirect
-	go.opentelemetry.io/otel/sdk v1.20.0 // indirect
-	go.opentelemetry.io/otel/trace v1.20.0 // indirect
-	go.opentelemetry.io/proto/otlp v1.0.0 // indirect
 	go.uber.org/atomic v1.7.0 // indirect
 	go.uber.org/multierr v1.6.0 // indirect
 	golang.org/x/net v0.17.0 // indirect