Remote sampling support - AWS X-Ray

.github/dependabot.yml

@@ -723,3 +723,13 @@ updates:
     schedule:
       interval: "weekly"
       day: "sunday"
+  -
+    package-ecosystem: "gomod"
+    directory: "/samplers/aws/xray"
+    labels:
+      - dependencies
+      - go
+      - "Skip Changelog"
+    schedule:
+      interval: "weekly"
+      day: "sunday"

samplers/aws/xray/fallback_sampler.go

@@ -0,0 +1,101 @@
+// Copyright The OpenTelemetry 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 xray // import "go.opentelemetry.io/contrib/samplers/aws/xray"
+
+import (
+	"sync"
+	"time"
+
+	sdktrace "go.opentelemetry.io/otel/sdk/trace"
+	"go.opentelemetry.io/otel/trace"
+)
+
+type FallbackSampler struct {
+	lastTick       time.Time
+	quotaBalance   float64
+	defaultSampler sdktrace.Sampler
+	mu             sync.RWMutex
+}
+
+// Compile time assertion that remoteSampler implements the Sampler interface.
+var _ sdktrace.Sampler = (*FallbackSampler)(nil)
+
+// NewFallbackSampler returns a FallbackSampler which samples 1 req/sec and additional 5% of requests using traceIDRatioBasedSampler.
+func NewFallbackSampler() *FallbackSampler {
+	return &FallbackSampler{
+		defaultSampler: sdktrace.TraceIDRatioBased(0.05),
+		quotaBalance:   1.0,
+	}
+}
+
+// ShouldSample implements the logic of borrowing 1 req/sec and then use traceIDRatioBasedSampler to sample 5% of additional requests.
+func (fs *FallbackSampler) ShouldSample(parameters sdktrace.SamplingParameters) sdktrace.SamplingResult {
+	// borrowing one request every second
+	if fs.take(time.Now(), 1.0) {
+		return sdktrace.SamplingResult{
+			Tracestate: trace.SpanContextFromContext(parameters.ParentContext).TraceState(),
+			Decision:   sdktrace.RecordAndSample,
+		}
+	}
+
+	// traceIDRatioBasedSampler to sample 5% of additional requests every second
+	return fs.defaultSampler.ShouldSample(parameters)
+}
+
+// Description returns description of the sampler being used
+func (fs *FallbackSampler) Description() string {
+	return "FallbackSampler{fallback sampling with sampling config of 1 req/sec and 5% of additional requests}"
+}
+
+// take consumes quota from reservoir, if any remains, then returns true. False otherwise.
+func (fs *FallbackSampler) take(now time.Time, itemCost float64) bool {
+	fs.mu.Lock()
+	defer fs.mu.Unlock()
+
+	if fs.lastTick.IsZero() {
+		fs.lastTick = now
+	}
+
+	if fs.quotaBalance >= itemCost {
+		fs.quotaBalance -= itemCost
+		return true
+	}
+
+	// update quota balance based on elapsed time
+	fs.refreshQuotaBalance(now)
+
+	if fs.quotaBalance >= itemCost {
+		fs.quotaBalance -= itemCost
+		return true
+	}
+
+	return false
+}
+
+// refreshQuotaBalance refreshes the quotaBalance considering elapsedTime.
+func (fs *FallbackSampler) refreshQuotaBalance(now time.Time) {
+	currentTime := now
+	elapsedTime := currentTime.Sub(fs.lastTick)
+	fs.lastTick = currentTime
+
+	// when elapsedTime is higher than 1 even then we need to keep quotaBalance
+	// near to 1 so making elapsedTime to 1 for only borrowing 1 per second case
+	if elapsedTime.Seconds() > 1.0 {
+		fs.quotaBalance += 1.0
+	} else {
+		// calculate how much credit have we accumulated since the last tick
+		fs.quotaBalance += elapsedTime.Seconds()
+	}
+}

samplers/aws/xray/fallback_sampler_test.go

@@ -0,0 +1,74 @@
+// Copyright The OpenTelemetry 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 xray
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+
+	"go.opentelemetry.io/otel/sdk/trace"
+)
+
+// assert sampling using fallback sampler.
+func TestSampleUsingFallbackSampler(t *testing.T) {
+	fs := NewFallbackSampler()
+	assert.NotEmpty(t, fs.defaultSampler)
+	assert.Equal(t, fs.quotaBalance, 1.0)
+
+	sd := fs.ShouldSample(trace.SamplingParameters{})
+	assert.Equal(t, trace.RecordAndSample, sd.Decision)
+}
+
+// assert that we only borrow 1 req/sec.
+func TestBorrowOnePerSecond(t *testing.T) {
+	fs := NewFallbackSampler()
+	borrowed := fs.take(time.Unix(1500000000, 0), 1.0)
+
+	// assert that borrowing one per second
+	assert.True(t, borrowed)
+
+	borrowed = fs.take(time.Unix(1500000000, 0), 1.0)
+
+	// assert that borrowing again is false during that second
+	assert.False(t, borrowed)
+
+	borrowed = fs.take(time.Unix(1500000001, 0), 1.0)
+
+	// assert that borrowing again in next second
+	assert.True(t, borrowed)
+}
+
+// assert that when elapsedTime is high quotaBalance should still be close to 1.
+func TestBorrowWithLargeElapsedTime(t *testing.T) {
+	fs := NewFallbackSampler()
+	borrowed := fs.take(time.Unix(1500000000, 0), 1.0)
+
+	// assert that borrowing one per second
+	assert.True(t, borrowed)
+
+	// Increase the time by 9 seconds
+	borrowed = fs.take(time.Unix(1500000009, 0), 1.0)
+	assert.True(t, borrowed)
+	assert.Equal(t, fs.quotaBalance, 0.0)
+}
+
+// assert fallback sampling description.
+func TestFallbackSamplerDescription(t *testing.T) {
+	fs := NewFallbackSampler()
+	s := fs.Description()
+	assert.Equal(t, s, "FallbackSampler{fallback sampling with sampling config of 1 req/sec and 5% of additional requests}")
+}

samplers/aws/xray/go.mod

@@ -0,0 +1,14 @@
+module go.opentelemetry.io/contrib/samplers/aws/xray
+
+go 1.16
+
+require (
+	github.com/go-logr/logr v1.2.2
+	github.com/go-logr/stdr v1.2.2
+	github.com/jinzhu/copier v0.3.5
+	github.com/stretchr/testify v1.7.0
+	go.opentelemetry.io/otel v1.4.0
+	go.opentelemetry.io/otel/sdk v1.4.0
+	go.opentelemetry.io/otel/trace v1.4.0
+	golang.org/x/sys v0.0.0-20210510120138-977fb7262007 // indirect
+)

samplers/aws/xray/go.sum

@@ -0,0 +1,29 @@
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