tracer: add CEL sampler to OpenTelemetry

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

@@ -8,5 +8,7 @@ api_proto_package(
     deps = [
         "//envoy/config/core/v3:pkg",
         "@com_github_cncf_xds//udpa/annotations:pkg",
+        "@com_github_cncf_xds//xds/annotations/v3:pkg",
+        "@com_github_cncf_xds//xds/type/v3:pkg",
     ],
 )

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

@@ -0,0 +1,25 @@
+syntax = "proto3";
+
+package envoy.extensions.tracers.opentelemetry.samplers.v3;
+
+import "xds/annotations/v3/status.proto";
+import "xds/type/v3/cel.proto";
+
+import "udpa/annotations/status.proto";
+
+option java_package = "io.envoyproxy.envoy.extensions.tracers.opentelemetry.samplers.v3";
+option java_outer_classname = "CelSamplerProto";
+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 "CEL" Sampler extension.
+//
+// [#extension: envoy.tracers.opentelemetry.samplers.cel]
+
+message CELSamplerConfig {
+  // Expression that, when evaluated, will be used to make sample decision.
+  xds.type.v3.CelExpression expression = 1
+      [(xds.annotations.v3.field_status).work_in_progress = true];
+}

bazel/repository_locations.bzl

@@ -600,6 +600,7 @@ REPOSITORY_LOCATIONS_SPEC = dict(
             "envoy.tracers.opentelemetry",
             "envoy.tracers.opentelemetry.samplers.always_on",
             "envoy.tracers.opentelemetry.samplers.dynatrace",
+            "envoy.tracers.opentelemetry.samplers.cel",
         ],
         release_date = "2025-01-22",
         cpe = "N/A",
@@ -1268,6 +1269,8 @@ REPOSITORY_LOCATIONS_SPEC = dict(
             "envoy.formatter.cel",
             "envoy.matching.inputs.cel_data_input",
             "envoy.matching.matchers.cel_matcher",
+            "envoy.tracers.opentelemetry",
+            "envoy.tracers.opentelemetry.samplers.cel",
         ],
         release_date = "2024-10-25",
         cpe = "N/A",
@@ -1299,6 +1302,8 @@ REPOSITORY_LOCATIONS_SPEC = dict(
             "envoy.rbac.matchers.upstream_ip_port",
             "envoy.matching.inputs.cel_data_input",
             "envoy.matching.matchers.cel_matcher",
+            "envoy.tracers.opentelemetry",
+            "envoy.tracers.opentelemetry.samplers.cel",
         ],
         release_date = "2025-01-25",
         cpe = "cpe:2.3:a:google:flatbuffers:*",

source/extensions/extensions_build_config.bzl

@@ -298,6 +298,7 @@ EXTENSIONS = {
 
     "envoy.tracers.opentelemetry.samplers.always_on":         "//source/extensions/tracers/opentelemetry/samplers/always_on:config",
     "envoy.tracers.opentelemetry.samplers.dynatrace":         "//source/extensions/tracers/opentelemetry/samplers/dynatrace:config",
+    "envoy.tracers.opentelemetry.samplers.cel":               "//source/extensions/tracers/opentelemetry/samplers/cel:config",
 
     #
     # Transport sockets

source/extensions/extensions_metadata.yaml

@@ -1266,6 +1266,13 @@ envoy.tracers.opentelemetry.samplers.dynatrace:
   status: wip
   type_urls:
   - envoy.extensions.tracers.opentelemetry.samplers.v3.DynatraceSamplerConfig
+envoy.tracers.opentelemetry.samplers.cel:
+  categories:
+  - envoy.tracers.opentelemetry.samplers
+  security_posture: unknown
+  status: wip
+  type_urls:
+  - envoy.extensions.tracers.opentelemetry.samplers.v3.CELSamplerConfig
 envoy.tracers.skywalking:
   categories:
   - envoy.tracers

source/extensions/filters/common/expr/BUILD

@@ -18,6 +18,7 @@ envoy_cc_library(
         "//envoy/singleton:manager_interface",
         "//source/common/http:utility_lib",
         "//source/common/protobuf",
+        "@com_github_cncf_xds//xds/type/v3:pkg_cc_proto",
         "@com_google_cel_cpp//eval/public:activation",
         "@com_google_cel_cpp//eval/public:builtin_func_registrar",
         "@com_google_cel_cpp//eval/public:cel_expr_builder_factory",

source/extensions/filters/common/expr/evaluator.cc

@@ -5,6 +5,7 @@
 
 #include "extensions/regex_functions.h"
 
+#include "cel/expr/syntax.pb.h"
 #include "eval/public/builtin_func_registrar.h"
 #include "eval/public/cel_expr_builder_factory.h"
 
@@ -141,6 +142,32 @@ BuilderInstanceSharedPtr getBuilder(Server::Configuration::CommonFactoryContext&
       [] { return std::make_shared<BuilderInstance>(createBuilder(nullptr)); });
 }
 
+// Converts from CEL canonical to CEL v1alpha1
+absl::optional<google::api::expr::v1alpha1::Expr>
+getExpr(const ::xds::type::v3::CelExpression& expression) {
+  ::cel::expr::Expr expr;
+  if (expression.has_cel_expr_checked()) {
+    expr = expression.cel_expr_checked().expr();
+  } else if (expression.has_cel_expr_parsed()) {
+    expr = expression.cel_expr_parsed().expr();
+  } else {
+    return {};
+  }
+
+  std::string data;
+  if (!expr.SerializeToString(&data)) {
+    return {};
+  }
+
+  // Parse the string into the target namespace message
+  google::api::expr::v1alpha1::Expr v1alpha1Expr;
+  if (!v1alpha1Expr.ParseFromString(data)) {
+    return {};
+  }
+
+  return v1alpha1Expr;
+}
+
 ExpressionPtr createExpression(Builder& builder, const google::api::expr::v1alpha1::Expr& expr) {
   google::api::expr::v1alpha1::SourceInfo source_info;
   auto cel_expression_status = builder.CreateExpression(&expr, &source_info);

source/extensions/filters/common/expr/evaluator.h

@@ -17,6 +17,8 @@
 #include "eval/public/cel_expression.h"
 #include "eval/public/cel_value.h"
 
+#include "xds/type/v3/cel.pb.h"
+
 #if defined(__GNUC__)
 #pragma GCC diagnostic pop
 #endif
@@ -92,6 +94,10 @@ BuilderPtr createBuilder(Protobuf::Arena* arena);
 // Gets the singleton expression builder. Must be called on the main thread.
 BuilderInstanceSharedPtr getBuilder(Server::Configuration::CommonFactoryContext& context);
 
+// Converts from CEL canonical to CEL v1alpha1
+absl::optional<google::api::expr::v1alpha1::Expr>
+getExpr(const ::xds::type::v3::CelExpression& expression);
+
 // Creates an interpretable expression from a protobuf representation.
 // Throws an exception if fails to construct a runtime expression.
 ExpressionPtr createExpression(Builder& builder, const google::api::expr::v1alpha1::Expr& expr);

source/extensions/tracers/opentelemetry/opentelemetry_tracer_impl.cc

@@ -119,15 +119,16 @@ Tracing::SpanPtr Driver::startSpan(const Tracing::Config& config,
   const auto span_kind = getSpanKind(config);
   if (!extractor.propagationHeaderPresent()) {
     // No propagation header, so we can create a fresh span with the given decision.
-    Tracing::SpanPtr new_open_telemetry_span = tracer.startSpan(
-        operation_name, stream_info.startTime(), tracing_decision, trace_context, span_kind);
+    Tracing::SpanPtr new_open_telemetry_span =
+        tracer.startSpan(operation_name, stream_info, stream_info.startTime(), tracing_decision,
+                         trace_context, span_kind);
     return new_open_telemetry_span;
   } else {
     // Try to extract the span context. If we can't, just return a null span.
     absl::StatusOr<SpanContext> span_context = extractor.extractSpanContext();
     if (span_context.ok()) {
-      return tracer.startSpan(operation_name, stream_info.startTime(), span_context.value(),
-                              trace_context, span_kind);
+      return tracer.startSpan(operation_name, stream_info, stream_info.startTime(),
+                              span_context.value(), trace_context, span_kind);
     } else {
       ENVOY_LOG(trace, "Unable to extract span context: ", span_context.status());
       return std::make_unique<Tracing::NullSpan>();

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

@@ -12,7 +12,8 @@ namespace Extensions {
 namespace Tracers {
 namespace OpenTelemetry {
 
-SamplingResult AlwaysOnSampler::shouldSample(const absl::optional<SpanContext> parent_context,
+SamplingResult AlwaysOnSampler::shouldSample(const StreamInfo::StreamInfo&,
+                                             const absl::optional<SpanContext> parent_context,
                                              const std::string& /*trace_id*/,
                                              const std::string& /*name*/, OTelSpanKind /*kind*/,
                                              OptRef<const Tracing::TraceContext> /*trace_context*/,

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

@@ -22,7 +22,8 @@ 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,
+  SamplingResult shouldSample(const StreamInfo::StreamInfo& stream_info,
+                              const absl::optional<SpanContext> parent_context,
                               const std::string& trace_id, const std::string& name,
                               OTelSpanKind spankind,
                               OptRef<const Tracing::TraceContext> trace_context,

source/extensions/tracers/opentelemetry/samplers/cel/BUILD

@@ -0,0 +1,37 @@
+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"],
+    tags = ["skip_on_windows"],
+    deps = [
+        ":cel_sampler_lib",
+        "//envoy/registry",
+        "//source/common/config:utility_lib",
+        "//source/extensions/filters/common/expr:evaluator_lib",
+        "@envoy_api//envoy/extensions/tracers/opentelemetry/samplers/v3:pkg_cc_proto",
+    ],
+)
+
+envoy_cc_library(
+    name = "cel_sampler_lib",
+    srcs = ["cel_sampler.cc"],
+    hdrs = ["cel_sampler.h"],
+    deps = [
+        "//source/common/config:datasource_lib",
+        "//source/extensions/filters/common/expr:evaluator_lib",
+        "//source/extensions/tracers/opentelemetry:opentelemetry_tracer_lib",
+        "//source/extensions/tracers/opentelemetry/samplers:sampler_lib",
+        "@envoy_api//envoy/extensions/tracers/opentelemetry/samplers/v3:pkg_cc_proto",
+    ],
+)

source/extensions/tracers/opentelemetry/samplers/cel/cel_sampler.cc

@@ -0,0 +1,57 @@
+#include "source/extensions/tracers/opentelemetry/samplers/cel/cel_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 {
+
+CELSampler::CELSampler(const ::Envoy::LocalInfo::LocalInfo& local_info,
+                       Expr::BuilderInstanceSharedPtr builder,
+                       const google::api::expr::v1alpha1::Expr& expr)
+    : local_info_(local_info), builder_(builder), parsed_expr_(expr) {
+  compiled_expr_ = Expr::createExpression(builder_->builder(), parsed_expr_);
+}
+
+SamplingResult CELSampler::shouldSample(const StreamInfo::StreamInfo& stream_info,
+                                        const absl::optional<SpanContext> parent_context,
+                                        const std::string& /*trace_id*/,
+                                        const std::string& /*name*/, OTelSpanKind /*kind*/,
+                                        OptRef<const Tracing::TraceContext>,
+                                        const std::vector<SpanContext>& /*links*/) {
+
+  Protobuf::Arena arena;
+  auto eval_status = Expr::evaluate(*compiled_expr_, arena, &local_info_, stream_info,
+                                    nullptr /* request_headers */, nullptr /* response_headers */,
+                                    nullptr /* response_trailers */);
+  SamplingResult result;
+  if (!eval_status.has_value() || eval_status.value().IsError()) {
+    result.decision = Decision::Drop;
+    return result;
+  }
+  auto eval_result_val = eval_status.value();
+  auto eval_result = eval_result_val.IsBool() ? eval_result_val.BoolOrDie() : false;
+  if (!eval_result) {
+    result.decision = Decision::Drop;
+    return result;
+  }
+
+  result.decision = Decision::RecordAndSample;
+  if (parent_context.has_value()) {
+    result.tracestate = parent_context.value().tracestate();
+  }
+  return result;
+}
+
+std::string CELSampler::getDescription() const { return "CELSampler"; }
+
+} // namespace OpenTelemetry
+} // namespace Tracers
+} // namespace Extensions
+} // namespace Envoy

source/extensions/tracers/opentelemetry/samplers/cel/cel_sampler.h

@@ -0,0 +1,47 @@
+#pragma once
+
+#include "envoy/extensions/tracers/opentelemetry/samplers/v3/cel_sampler.pb.h"
+#include "envoy/server/factory_context.h"
+
+#include "source/common/common/logger.h"
+#include "source/common/config/datasource.h"
+#include "source/extensions/filters/common/expr/evaluator.h"
+#include "source/extensions/tracers/opentelemetry/samplers/sampler.h"
+
+namespace Envoy {
+namespace Extensions {
+namespace Tracers {
+namespace OpenTelemetry {
+
+namespace Expr = Envoy::Extensions::Filters::Common::Expr;
+
+/**
+ * @brief A sampler which samples on CEL expression.
+ *
+ * - Returns RecordAndSample always.
+ * - Description MUST be AlwaysOnSampler.
+ *
+ */
+class CELSampler : public Sampler, Logger::Loggable<Logger::Id::tracing> {
+public:
+  CELSampler(const ::Envoy::LocalInfo::LocalInfo& local_info,
+             Expr::BuilderInstanceSharedPtr builder, const google::api::expr::v1alpha1::Expr& expr);
+  SamplingResult shouldSample(const StreamInfo::StreamInfo& stream_info,
+                              const absl::optional<SpanContext> parent_context,
+                              const std::string& trace_id, const std::string& name,
+                              OTelSpanKind spankind,
+                              OptRef<const Tracing::TraceContext> trace_context,
+                              const std::vector<SpanContext>& links) override;
+  std::string getDescription() const override;
+
+private:
+  const ::Envoy::LocalInfo::LocalInfo& local_info_;
+  Extensions::Filters::Common::Expr::BuilderInstanceSharedPtr builder_;
+  const google::api::expr::v1alpha1::Expr parsed_expr_;
+  Extensions::Filters::Common::Expr::ExpressionPtr compiled_expr_;
+};
+
+} // namespace OpenTelemetry
+} // namespace Tracers
+} // namespace Extensions
+} // namespace Envoy

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

@@ -0,0 +1,44 @@
+#include "source/extensions/tracers/opentelemetry/samplers/cel/config.h"
+
+#include <memory>
+
+#include "envoy/extensions/tracers/opentelemetry/samplers/v3/cel_sampler.pb.validate.h"
+
+#include "source/common/config/utility.h"
+#include "source/common/protobuf/utility.h"
+#include "source/extensions/tracers/opentelemetry/samplers/cel/cel_sampler.h"
+
+namespace Envoy {
+namespace Extensions {
+namespace Tracers {
+namespace OpenTelemetry {
+
+SamplerSharedPtr
+CELSamplerFactory::createSampler(const Protobuf::Message& config,
+                                 Server::Configuration::TracerFactoryContext& context) {
+  auto mptr = Envoy::Config::Utility::translateAnyToFactoryConfig(
+      dynamic_cast<const ProtobufWkt::Any&>(config), context.messageValidationVisitor(), *this);
+
+  const auto& proto_config = MessageUtil::downcastAndValidate<
+      const envoy::extensions::tracers::opentelemetry::samplers::v3::CELSamplerConfig&>(
+      *mptr, context.messageValidationVisitor());
+
+  auto expr = Expr::getExpr(proto_config.expression());
+  if (!expr.has_value()) {
+    throw EnvoyException("CEL expression not set");
+  }
+
+  return std::make_unique<CELSampler>(
+      context.serverFactoryContext().localInfo(),
+      Extensions::Filters::Common::Expr::getBuilder(context.serverFactoryContext()), expr.value());
+}
+
+/**
+ * Static registration for the Env sampler factory. @see RegisterFactory.
+ */
+REGISTER_FACTORY(CELSamplerFactory, SamplerFactory);
+
+} // namespace OpenTelemetry
+} // namespace Tracers
+} // namespace Extensions
+} // namespace Envoy