add sampler interface and AlwaysOnSampler

api/BUILD

@@ -300,6 +300,7 @@ proto_library(
         "//envoy/extensions/stat_sinks/graphite_statsd/v3:pkg",
         "//envoy/extensions/stat_sinks/open_telemetry/v3:pkg",
         "//envoy/extensions/stat_sinks/wasm/v3:pkg",
+        "//envoy/extensions/tracers/opentelemetry/samplers/v3:pkg",
         "//envoy/extensions/transport_sockets/alts/v3:pkg",
         "//envoy/extensions/transport_sockets/http_11_proxy/v3:pkg",
         "//envoy/extensions/transport_sockets/internal_upstream/v3:pkg",

api/envoy/config/trace/v3/opentelemetry.proto

@@ -2,6 +2,7 @@ syntax = "proto3";
 
 package envoy.config.trace.v3;
 
+import "envoy/config/core/v3/extension.proto";
 import "envoy/config/core/v3/grpc_service.proto";
 
 import "udpa/annotations/status.proto";
@@ -25,4 +26,12 @@ message OpenTelemetryConfig {
   // The name for the service. This will be populated in the ResourceSpan Resource attributes.
   // If it is not provided, it will default to "unknown_service:envoy".
   string service_name = 2;
+
+  // Specifies the sampler to be used by the OpenTelemetry tracer.
+  // The configured sampler implements the Sampler interface defined by the OpenTelemetry specification.
+  // This field can be left empty. In this case, the default Envoy sampling decision is used.
+  //
+  // See: `OpenTelemetry sampler specification <https://opentelemetry.io/docs/specs/otel/trace/sdk/#sampler>`_
+  // [#extension-category: envoy.tracers.opentelemetry.samplers]
+  core.v3.TypedExtensionConfig sampler = 3;
 }

api/envoy/extensions/tracers/opentelemetry/samplers/v3/BUILD

@@ -0,0 +1,9 @@
+# DO NOT EDIT. This file is generated by tools/proto_format/proto_sync.py.
+
+load("@envoy_api//bazel:api_build_system.bzl", "api_proto_package")
+
+licenses(["notice"])  # Apache 2
+
+api_proto_package(
+    deps = ["@com_github_cncf_udpa//udpa/annotations:pkg"],
+)

api/envoy/extensions/tracers/opentelemetry/samplers/v3/always_on_sampler.proto

@@ -0,0 +1,23 @@
+syntax = "proto3";
+
+package envoy.extensions.tracers.opentelemetry.samplers.v3;
+
+import "udpa/annotations/status.proto";
+
+option java_package = "io.envoyproxy.envoy.extensions.tracers.opentelemetry.samplers.v3";
+option java_outer_classname = "AlwaysOnSamplerProto";
+option java_multiple_files = true;
+option go_package = "github.com/envoyproxy/go-control-plane/envoy/extensions/tracers/opentelemetry/samplers/v3;samplersv3";
+option (udpa.annotations.file_status).package_version_status = ACTIVE;
+
+// [#protodoc-title: Always On Sampler config]
+// Configuration for the "AlwaysOn" Sampler extension.
+// The sampler follows the "AlwaysOn" implementation from the OpenTelemetry
+// SDK specification.
+//
+// See:
+// `AlwaysOn sampler specification <https://opentelemetry.io/docs/specs/otel/trace/sdk/#alwayson>`_
+// [#extension: envoy.tracers.opentelemetry.samplers.always_on]
+
+message AlwaysOnSamplerConfig {
+}

api/versioning/BUILD

@@ -239,6 +239,7 @@ proto_library(
         "//envoy/extensions/stat_sinks/graphite_statsd/v3:pkg",
         "//envoy/extensions/stat_sinks/open_telemetry/v3:pkg",
         "//envoy/extensions/stat_sinks/wasm/v3:pkg",
+        "//envoy/extensions/tracers/opentelemetry/samplers/v3:pkg",
         "//envoy/extensions/transport_sockets/alts/v3:pkg",
         "//envoy/extensions/transport_sockets/http_11_proxy/v3:pkg",
         "//envoy/extensions/transport_sockets/internal_upstream/v3:pkg",

docs/root/api-v3/config/trace/opentelemetry/samplers.rst

@@ -0,0 +1,10 @@
+OpenTelemetry Samplers
+======================
+
+Samplers that can be configured with the OpenTelemetry Tracer:
+
+.. toctree::
+  :glob:
+  :maxdepth: 3
+
+  ../../../extensions/tracers/opentelemetry/samplers/v3/*

docs/root/api-v3/config/trace/trace.rst

@@ -12,3 +12,4 @@ HTTP tracers
   :maxdepth: 2
 
   v3/*
+  opentelemetry/samplers

source/extensions/extensions_build_config.bzl

@@ -260,6 +260,12 @@ EXTENSIONS = {
     "envoy.tracers.skywalking":                         "//source/extensions/tracers/skywalking:config",
     "envoy.tracers.opentelemetry":                      "//source/extensions/tracers/opentelemetry:config",
 
+    #
+    # OpenTelemetry tracer samplers
+    #
+
+    "envoy.tracers.opentelemetry.samplers.always_on":         "//source/extensions/tracers/opentelemetry/samplers/always_on:config",
+
     #
     # Transport sockets
     #

source/extensions/extensions_metadata.yaml

@@ -1136,6 +1136,11 @@ envoy.tracers.opentelemetry:
   status: wip
   type_urls:
   - envoy.config.trace.v3.OpenTelemetryConfig
+envoy.tracers.opentelemetry.samplers.always_on:
+  categories:
+  - envoy.tracers.opentelemetry.samplers
+  security_posture: unknown
+  status: wip
 envoy.tracers.skywalking:
   categories:
   - envoy.tracers

source/extensions/tracers/opentelemetry/BUILD

@@ -41,6 +41,7 @@ envoy_cc_library(
         "//source/common/config:utility_lib",
         "//source/common/tracing:http_tracer_lib",
         "//source/extensions/tracers/common:factory_base_lib",
+        "//source/extensions/tracers/opentelemetry/samplers:sampler_lib",
         "@envoy_api//envoy/config/trace/v3:pkg_cc_proto",
         "@opentelemetry_proto//:trace_cc_proto",
     ],

source/extensions/tracers/opentelemetry/opentelemetry_tracer_impl.cc

@@ -8,6 +8,7 @@
 #include "source/common/common/logger.h"
 #include "source/common/config/utility.h"
 #include "source/common/tracing/http_tracer_impl.h"
+#include "source/extensions/tracers/opentelemetry/samplers/sampler.h"
 
 #include "opentelemetry/proto/collector/trace/v1/trace_service.pb.h"
 #include "opentelemetry/proto/trace/v1/trace.pb.h"
@@ -20,29 +21,54 @@ namespace Extensions {
 namespace Tracers {
 namespace OpenTelemetry {
 
+namespace {
+
+SamplerSharedPtr
+tryCreateSamper(const envoy::config::trace::v3::OpenTelemetryConfig& opentelemetry_config,
+                Server::Configuration::TracerFactoryContext& context) {
+  SamplerSharedPtr sampler;
+  if (opentelemetry_config.has_sampler()) {
+    auto& sampler_config = opentelemetry_config.sampler();
+    auto* factory = Envoy::Config::Utility::getFactory<SamplerFactory>(sampler_config);
+    if (!factory) {
+      throw EnvoyException(fmt::format("Sampler factory not found: '{}'", sampler_config.name()));
+    }
+    sampler = factory->createSampler(sampler_config.typed_config(), context);
+  }
+  return sampler;
+}
+
+} // namespace
+
 Driver::Driver(const envoy::config::trace::v3::OpenTelemetryConfig& opentelemetry_config,
                Server::Configuration::TracerFactoryContext& context)
     : tls_slot_ptr_(context.serverFactoryContext().threadLocal().allocateSlot()),
       tracing_stats_{OPENTELEMETRY_TRACER_STATS(
           POOL_COUNTER_PREFIX(context.serverFactoryContext().scope(), "tracing.opentelemetry"))} {
   auto& factory_context = context.serverFactoryContext();
+
+  // Create the sampler if configured
+  SamplerSharedPtr sampler = tryCreateSamper(opentelemetry_config, context);
+
   // Create the tracer in Thread Local Storage.
-  tls_slot_ptr_->set([opentelemetry_config, &factory_context, this](Event::Dispatcher& dispatcher) {
-    OpenTelemetryGrpcTraceExporterPtr exporter;
-    if (opentelemetry_config.has_grpc_service()) {
-      Grpc::AsyncClientFactoryPtr&& factory =
-          factory_context.clusterManager().grpcAsyncClientManager().factoryForGrpcService(
-              opentelemetry_config.grpc_service(), factory_context.scope(), true);
-      const Grpc::RawAsyncClientSharedPtr& async_client_shared_ptr =
-          factory->createUncachedRawAsyncClient();
-      exporter = std::make_unique<OpenTelemetryGrpcTraceExporter>(async_client_shared_ptr);
-    }
-    TracerPtr tracer = std::make_unique<Tracer>(
-        std::move(exporter), factory_context.timeSource(), factory_context.api().randomGenerator(),
-        factory_context.runtime(), dispatcher, tracing_stats_, opentelemetry_config.service_name());
+  tls_slot_ptr_->set(
+      [opentelemetry_config, &factory_context, this, sampler](Event::Dispatcher& dispatcher) {
+        OpenTelemetryGrpcTraceExporterPtr exporter;
+        if (opentelemetry_config.has_grpc_service()) {
+          Grpc::AsyncClientFactoryPtr&& factory =
+              factory_context.clusterManager().grpcAsyncClientManager().factoryForGrpcService(
+                  opentelemetry_config.grpc_service(), factory_context.scope(), true);
+          const Grpc::RawAsyncClientSharedPtr& async_client_shared_ptr =
+              factory->createUncachedRawAsyncClient();
+          exporter = std::make_unique<OpenTelemetryGrpcTraceExporter>(async_client_shared_ptr);
+        }
+        TracerPtr tracer = std::make_unique<Tracer>(
+            std::move(exporter), factory_context.timeSource(),
+            factory_context.api().randomGenerator(), factory_context.runtime(), dispatcher,
+            tracing_stats_, opentelemetry_config.service_name(), sampler);
 
-    return std::make_shared<TlsTracer>(std::move(tracer));
-  });
+        return std::make_shared<TlsTracer>(std::move(tracer));
+      });
 }
 
 Tracing::SpanPtr Driver::startSpan(const Tracing::Config& config,
@@ -57,7 +83,6 @@ Tracing::SpanPtr Driver::startSpan(const Tracing::Config& config,
     // No propagation header, so we can create a fresh span with the given decision.
     Tracing::SpanPtr new_open_telemetry_span =
         tracer.startSpan(config, operation_name, stream_info.startTime(), tracing_decision);
-    new_open_telemetry_span->setSampled(tracing_decision.traced);
     return new_open_telemetry_span;
   } else {
     // Try to extract the span context. If we can't, just return a null span.

source/extensions/tracers/opentelemetry/samplers/BUILD

@@ -0,0 +1,25 @@
+load(
+    "//bazel:envoy_build_system.bzl",
+    "envoy_cc_library",
+    "envoy_extension_package",
+)
+
+licenses(["notice"])  # Apache 2
+
+envoy_extension_package()
+
+envoy_cc_library(
+    name = "sampler_lib",
+    srcs = [
+    ],
+    hdrs = [
+        "sampler.h",
+    ],
+    deps = [
+        "//envoy/config:typed_config_interface",
+        "//envoy/server:tracer_config_interface",
+        "//source/common/common:logger_lib",
+        "//source/common/config:utility_lib",
+        "@opentelemetry_proto//:trace_cc_proto",
+    ],
+)

source/extensions/tracers/opentelemetry/samplers/always_on/BUILD

@@ -0,0 +1,33 @@
+load(
+    "//bazel:envoy_build_system.bzl",
+    "envoy_cc_extension",
+    "envoy_cc_library",
+    "envoy_extension_package",
+)
+
+licenses(["notice"])  # Apache 2
+
+envoy_extension_package()
+
+envoy_cc_extension(
+    name = "config",
+    srcs = ["config.cc"],
+    hdrs = ["config.h"],
+    deps = [
+        ":always_on_sampler_lib",
+        "//envoy/registry",
+        "//source/common/config:utility_lib",
+        "@envoy_api//envoy/extensions/tracers/opentelemetry/samplers/v3:pkg_cc_proto",
+    ],
+)
+
+envoy_cc_library(
+    name = "always_on_sampler_lib",
+    srcs = ["always_on_sampler.cc"],
+    hdrs = ["always_on_sampler.h"],
+    deps = [
+        "//source/common/config:datasource_lib",
+        "//source/extensions/tracers/opentelemetry:opentelemetry_tracer_lib",
+        "//source/extensions/tracers/opentelemetry/samplers:sampler_lib",
+    ],
+)

source/extensions/tracers/opentelemetry/samplers/always_on/always_on_sampler.cc

@@ -0,0 +1,34 @@
+#include "source/extensions/tracers/opentelemetry/samplers/always_on/always_on_sampler.h"
+
+#include <memory>
+#include <sstream>
+#include <string>
+
+#include "source/common/config/datasource.h"
+#include "source/extensions/tracers/opentelemetry/span_context.h"
+
+namespace Envoy {
+namespace Extensions {
+namespace Tracers {
+namespace OpenTelemetry {
+
+SamplingResult
+AlwaysOnSampler::shouldSample(const absl::optional<SpanContext> parent_context,
+                              const std::string& /*trace_id*/, const std::string& /*name*/,
+                              ::opentelemetry::proto::trace::v1::Span::SpanKind /*kind*/,
+                              const std::map<std::string, std::string>& /*attributes*/,
+                              const std::vector<SpanContext>& /*links*/) {
+  SamplingResult result;
+  result.decision = Decision::RECORD_AND_SAMPLE;
+  if (parent_context.has_value()) {
+    result.tracestate = parent_context.value().tracestate();
+  }
+  return result;
+}
+
+std::string AlwaysOnSampler::getDescription() const { return "AlwaysOnSampler"; }
+
+} // namespace OpenTelemetry
+} // namespace Tracers
+} // namespace Extensions
+} // namespace Envoy

source/extensions/tracers/opentelemetry/samplers/always_on/always_on_sampler.h

@@ -0,0 +1,38 @@
+#pragma once
+
+#include "envoy/server/factory_context.h"
+
+#include "source/common/common/logger.h"
+#include "source/common/config/datasource.h"
+#include "source/extensions/tracers/opentelemetry/samplers/sampler.h"
+
+namespace Envoy {
+namespace Extensions {
+namespace Tracers {
+namespace OpenTelemetry {
+
+/**
+ * @brief A sampler which samples every span.
+ * https://opentelemetry.io/docs/specs/otel/trace/sdk/#alwayson
+ * - Returns RECORD_AND_SAMPLE always.
+ * - Description MUST be AlwaysOnSampler.
+ *
+ */
+class AlwaysOnSampler : public Sampler, Logger::Loggable<Logger::Id::tracing> {
+public:
+  explicit AlwaysOnSampler(const Protobuf::Message& /*config*/,
+                           Server::Configuration::TracerFactoryContext& /*context*/) {}
+  SamplingResult shouldSample(const absl::optional<SpanContext> parent_context,
+                              const std::string& trace_id, const std::string& name,
+                              ::opentelemetry::proto::trace::v1::Span::SpanKind spankind,
+                              const std::map<std::string, std::string>& attributes,
+                              const std::vector<SpanContext>& links) override;
+  std::string getDescription() const override;
+
+private:
+};
+
+} // namespace OpenTelemetry
+} // namespace Tracers
+} // namespace Extensions
+} // namespace Envoy

source/extensions/tracers/opentelemetry/samplers/always_on/config.cc

@@ -0,0 +1,27 @@
+#include "source/extensions/tracers/opentelemetry/samplers/always_on/config.h"
+
+#include "envoy/server/tracer_config.h"
+
+#include "source/common/config/utility.h"
+#include "source/extensions/tracers/opentelemetry/samplers/always_on/always_on_sampler.h"
+
+namespace Envoy {
+namespace Extensions {
+namespace Tracers {
+namespace OpenTelemetry {
+
+SamplerSharedPtr
+AlwaysOnSamplerFactory::createSampler(const Protobuf::Message& config,
+                                      Server::Configuration::TracerFactoryContext& context) {
+  return std::make_shared<AlwaysOnSampler>(config, context);
+}
+
+/**
+ * Static registration for the Env sampler factory. @see RegisterFactory.
+ */
+REGISTER_FACTORY(AlwaysOnSamplerFactory, SamplerFactory);
+
+} // namespace OpenTelemetry
+} // namespace Tracers
+} // namespace Extensions
+} // namespace Envoy