Introduce Satellite sampler package

lightstep/processor/satellitesamplerprocessor/README.md

@@ -0,0 +1,103 @@
+# Lightstep Satellite Sampler
+
+This package contains an OpenTelemetry processor for an OpenTelemetry
+traces pipeline that makes sampling decisions consistent with the
+legacy Lightstep Satellite.  This component enables a slow transition
+from Lightstep Satellites to OpenTelemetry Collectors without
+simultaneously changing sampling algorithms.
+
+ ## Recommended usage
+
+This component supports operating a mixture of Lightstep Satellites
+and OpenTelemetry Collectors with consistent probability sampling.
+Here is a recommended sequence of steps for performing a migratation
+to OpenTelemetry Collectors for Lightstep Satellite users.
+
+### Build a custom OpenTelemetry Collector
+
+This component is provided as a standalone component, meant for
+incorporating into a custom build of the OpenTelemetry Collector using
+the [OpenTelemetry Collector
+builder](https://opentelemetry.io/docs/collector/custom-collector/)
+tool.  In your Collector's build configuration, add the following
+processor component:
+
+```
+  - gomod: github.com/lightstep/otel-collector-charts/lightstep/processor/satellitesamplerprocessor VERSIONTAG
+```
+
+where `VERSIONTAG` corresponds with the targetted OpenTelemetry
+Collector release version.  At the time of this writing, the version
+tag is `v0.109.0`.
+
+Users are advised to include the OpenTelemetry Probabilistic Sampler
+processor in their build, to complete this transition.  For example:
+
+```
+  - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/processor/probabilisticsamplerprocessor v0.109.0
+```
+
+Follow the usual steps to build your collector (e.g., `builder
+--config build.yaml`).
+
+### Configure the sampler
+
+You will need to know the sampling probability configured with
+Lightstep Satellites, in percentage terms.  Say the Lightstep
+Satellite is configured with 10% sampling (i.e., 1-in-10).
+
+Edit OpenTelemetry Collector configuration to include a
+`satellitesatempler` block.  In the following example, the OTel-Arrow
+receiver and exporter are configured with `satellitesampler` with 10%
+sampling and [concurrent batch
+processor](https://github.com/open-telemetry/otel-arrow/blob/main/collector/processor/concurrentbatchprocessor/README.md).
+
+```
+exporters:
+  otelarrow:
+    ...
+receivers:
+  otelarrow:
+    ...
+processors:
+  satellitesampler:
+    percent: 10
+  concurrentbatch:
+service:
+  pipelines:
+    traces:
+      receivers: [otelarrow]
+      processors: [satellitesampler, concurrentbatch]
+      exporters: [otelarrow]
+```
+
+Collectors with this configuration may be deployed alongside a pool of
+Lightstep Satellites sampling and the resulting traces will be
+complete.
+
+### Migrate to the OpenTelemetry Probabilistic Sampler
+
+After decomissioning Lightstep Satellites and replacing them with
+OpenTelemetry Collectors, users are advised to migrate to an
+OpenTelemetry Collector processor with equivalent functionality, the
+[Probabilistic Sampler Processor](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/processor/probabilisticsamplerprocessor/README.md).
+
+A change of sampling configuration, either to change algorithm or to
+change probability, typically results in broken traces.  Users are
+advised to plan accordingly and make a quick transition between
+samplers, with only a brief, planned period of broken traces.
+
+Redeploy the pool of Collectors with the Probabilistic Sampler
+processor configured instead of the Satellite sampler processor.  Make
+this transition quickly, if possible, because traces will be
+potentially incomplete as long as both samplers being used.
+
+```
+processors:
+  probabilisticsampler:
+    mode: equalizing
+	sampling_percentage: 10
+```
+
+The "equalizing" mode is recommended, see that [component's
+documentation](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/processor/probabilisticsamplerprocessor/README.md#equalizing).

lightstep/processor/satellitesamplerprocessor/config.go

@@ -0,0 +1,31 @@
+// Copyright ServiceNow, Inc
+// SPDX-License-Identifier: Apache-2.0
+
+package satellitesamplerprocessor
+
+import (
+	"errors"
+	"fmt"
+)
+
+var (
+	errInvalidPercent = errors.New("sampling percent must be in (0, 100]")
+)
+
+// Config defines configuration for Lightstep's "classic" Satellite sampler.
+type Config struct {
+	// Percent in the range (0, 100].  Defaults to 100.
+	//
+	// Note that satellites began supporting percent-based
+	// sampling configuration at release 2022-04-28_17-39-22Z.
+	// When OneInN is set instead, use the formula `100.0 /
+	// float64(OneInN)`.
+	Percent float64 `mapstructure:"percent"`
+}
+
+func (c *Config) Validate() error {
+	if c.Percent <= 0 || c.Percent > 100 {
+		return fmt.Errorf("%w: %v", errInvalidPercent, c.Percent)
+	}
+	return nil
+}

lightstep/processor/satellitesamplerprocessor/config_test.go

@@ -0,0 +1,25 @@
+// Copyright ServiceNow, Inc
+// SPDX-License-Identifier: Apache-2.0
+
+package satellitesamplerprocessor
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func testConfig(pct float64) *Config {
+	return &Config{Percent: pct}
+}
+
+func TestConfigValidate(t *testing.T) {
+	require.Error(t, testConfig(-1).Validate())
+	require.Error(t, testConfig(0).Validate())
+	require.Error(t, testConfig(101).Validate())
+
+	require.NoError(t, testConfig(1).Validate())
+	require.NoError(t, testConfig(50).Validate())
+	require.NoError(t, testConfig(99).Validate())
+	require.NoError(t, testConfig(100).Validate())
+}

lightstep/processor/satellitesamplerprocessor/factory.go

@@ -0,0 +1,46 @@
+// Copyright ServiceNow, Inc
+// SPDX-License-Identifier: Apache-2.0
+
+package satellitesamplerprocessor
+
+import (
+	"context"
+
+	"go.opentelemetry.io/collector/component"
+	"go.opentelemetry.io/collector/consumer"
+	"go.opentelemetry.io/collector/processor"
+	"go.opentelemetry.io/collector/processor/processorhelper"
+)
+
+const (
+	typeStr   = "satellitesampler"
+	stability = component.StabilityLevelStable
+)
+
+func NewFactory() processor.Factory {
+	return processor.NewFactory(
+		component.MustNewType(typeStr),
+		createDefaultConfig,
+		processor.WithTraces(createTracesProcessorHelper, stability),
+	)
+}
+
+func createTracesProcessorHelper(ctx context.Context, set processor.Settings, cfg component.Config, nextConsumer consumer.Traces) (processor.Traces, error) {
+	tp, err := createTracesProcessor(ctx, set, cfg, nextConsumer)
+	if err != nil {
+		return nil, err
+	}
+	return processorhelper.NewTracesProcessor(
+		ctx,
+		set,
+		cfg,
+		nextConsumer,
+		tp.processTraces,
+		processorhelper.WithCapabilities(consumer.Capabilities{MutatesData: true}))
+}
+
+func createDefaultConfig() component.Config {
+	return &Config{
+		Percent: 100,
+	}
+}

lightstep/processor/satellitesamplerprocessor/factory_test.go

@@ -0,0 +1,15 @@
+// Copyright ServiceNow, Inc
+// SPDX-License-Identifier: Apache-2.0
+
+package satellitesamplerprocessor
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"go.opentelemetry.io/collector/component"
+)
+
+func TestDefaultConfig(t *testing.T) {
+	require.Equal(t, component.Config(testConfig(100)), createDefaultConfig())
+}

lightstep/processor/satellitesamplerprocessor/go.mod

@@ -0,0 +1,37 @@
+module github.com/lightstep/otel-collector-charts/lightstep/processor/satellitesamplerprocessor
+
+go 1.22.6
+
+require (
+	github.com/stretchr/testify v1.9.0
+	go.opentelemetry.io/collector/component v0.109.0
+	go.opentelemetry.io/collector/consumer v0.109.0
+	go.opentelemetry.io/collector/consumer/consumertest v0.109.0
+	go.opentelemetry.io/collector/pdata v1.15.0
+	go.opentelemetry.io/collector/processor v0.109.0
+	go.uber.org/multierr v1.11.0
+	go.uber.org/zap v1.27.0
+	google.golang.org/protobuf v1.34.2
+)
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/gogo/protobuf v1.3.2 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	go.opentelemetry.io/collector v0.109.0 // indirect
+	go.opentelemetry.io/collector/config/configtelemetry v0.109.0 // indirect
+	go.opentelemetry.io/collector/consumer/consumerprofiles v0.109.0 // indirect
+	go.opentelemetry.io/collector/pdata/pprofile v0.109.0 // indirect
+	go.opentelemetry.io/otel v1.29.0 // indirect
+	go.opentelemetry.io/otel/metric v1.29.0 // indirect
+	go.opentelemetry.io/otel/trace v1.29.0 // indirect
+	golang.org/x/net v0.28.0 // indirect
+	golang.org/x/sys v0.24.0 // indirect
+	golang.org/x/text v0.17.0 // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20240822170219-fc7c04adadcd // indirect
+	google.golang.org/grpc v1.66.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)