[CSM] Disable metrics recording when CsmObservability goes out of scope (#35835)

As discussed, this change adds scoping to `CsmObservability` such that when that object goes out of scope, new channels and servers don't record metrics. In the documentation, I've talked about how existing channels/servers are going to continue to record metrics but i've left room for us to change that behavior in the future.

The current way of doing this is through a global bool since there can only be one plugin right now, but we'll change this to use the global stats plugin registry in the future.

Closes #35835

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/35835 from yashykt:DisableCsmObsOnScope 33a7c2f7bc
PiperOrigin-RevId: 605468117

include/grpcpp/ext/csm_observability.h

@@ -38,16 +38,21 @@ class OpenTelemetryPluginBuilderImpl;
 
 namespace experimental {
 
-// This is a no-op at present, but in the future, this object would be useful
+// This object maintains state around the registered CsmObservability plugin.
-// for performing cleanup.
+// The application is responsible for retaining this object until it has closed
+// all channels and servers that are recording metrics.
 class CsmObservability {
  public:
   CsmObservability() = default;
+  ~CsmObservability();
   // Disable copy constructor and copy-assignment operator.
   CsmObservability(const CsmObservability&) = delete;
   CsmObservability& operator=(const CsmObservability&) = delete;
-  CsmObservability(CsmObservability&&) = default;
+  CsmObservability(CsmObservability&&) noexcept;
-  CsmObservability& operator=(CsmObservability&&) = default;
+  CsmObservability& operator=(CsmObservability&&) noexcept;
+
+ private:
+  bool valid_ = true;
 };
 
 // CsmObservabilityBuilder configures observability for all service mesh traffic

src/cpp/ext/csm/csm_observability.cc

@@ -45,11 +45,17 @@ namespace grpc {
 
 namespace internal {
 
+namespace {
+std::atomic<bool> g_csm_plugin_enabled(false);
+}
+
 bool CsmServerSelector(const grpc_core::ChannelArgs& args) {
-  return args.GetBool(GRPC_ARG_XDS_ENABLED_SERVER).value_or(false);
+  return g_csm_plugin_enabled &&
+         args.GetBool(GRPC_ARG_XDS_ENABLED_SERVER).value_or(false);
 }
 
 bool CsmChannelTargetSelector(absl::string_view target) {
+  if (!g_csm_plugin_enabled) return false;
   auto uri = grpc_core::URI::Parse(target);
   if (!uri.ok()) {
     gpr_log(GPR_ERROR, "Failed to parse URI: %s", std::string(target).c_str());
@@ -96,6 +102,25 @@ class CsmOpenTelemetryPluginOption
 
 namespace experimental {
 
+//
+// CsmObservability
+//
+
+CsmObservability::~CsmObservability() {
+  if (valid_) {
+    internal::g_csm_plugin_enabled = false;
+  }
+}
+
+CsmObservability::CsmObservability(CsmObservability&& other) noexcept {
+  other.valid_ = false;
+}
+CsmObservability& CsmObservability::operator=(
+    CsmObservability&& other) noexcept {
+  other.valid_ = false;
+  return *this;
+}
+
 //
 // CsmObservabilityBuilder
 //
@@ -132,6 +157,7 @@ absl::StatusOr<CsmObservability> CsmObservabilityBuilder::BuildAndRegister() {
   builder_->AddPluginOption(
       std::make_unique<grpc::internal::CsmOpenTelemetryPluginOption>());
   auto status = builder_->BuildAndRegisterGlobal();
+  internal::g_csm_plugin_enabled = true;
   if (!status.ok()) {
     return status;
   }

src/cpp/ext/csm/csm_observability.h

@@ -23,6 +23,8 @@
 
 #include "absl/strings/string_view.h"
 
+#include "src/core/lib/channel/channel_args.h"
+
 namespace grpc {
 namespace internal {
 
@@ -30,6 +32,10 @@ namespace internal {
 // Returns true if the channel is a CSM channel.
 bool CsmChannelTargetSelector(absl::string_view target);
 
+// EXPOSED FOR TESTING PURPOSES ONLY
+// Returns true if the server is a CSM server.
+bool CsmServerSelector(const grpc_core::ChannelArgs& args);
+
 }  // namespace internal
 }  // namespace grpc
 

test/cpp/ext/csm/csm_observability_test.cc

@@ -24,7 +24,7 @@
 #include <grpcpp/ext/csm_observability.h>
 #include <grpcpp/ext/otel_plugin.h>
 
-#include "src/core/lib/gprpp/env.h"
+#include "src/core/ext/xds/xds_enabled_server.h"
 #include "test/core/util/test_config.h"
 
 namespace grpc {
@@ -41,6 +41,7 @@ TEST(GsmDependencyTest, GoogleCloudOpenTelemetryDependency) {
 }
 
 TEST(CsmChannelTargetSelectorTest, NonXdsTargets) {
+  auto obs = experimental::CsmObservabilityBuilder().BuildAndRegister();
   EXPECT_FALSE(internal::CsmChannelTargetSelector("foo.bar.google.com"));
   EXPECT_FALSE(internal::CsmChannelTargetSelector("dns:///foo.bar.google.com"));
   EXPECT_FALSE(
@@ -50,19 +51,52 @@ TEST(CsmChannelTargetSelectorTest, NonXdsTargets) {
 }
 
 TEST(CsmChannelTargetSelectorTest, XdsTargets) {
+  auto obs = experimental::CsmObservabilityBuilder().BuildAndRegister();
   EXPECT_TRUE(internal::CsmChannelTargetSelector("xds:///foo"));
   EXPECT_TRUE(internal::CsmChannelTargetSelector("xds:///foo.bar"));
 }
 
 TEST(CsmChannelTargetSelectorTest, XdsTargetsWithNonTDAuthority) {
+  auto obs = experimental::CsmObservabilityBuilder().BuildAndRegister();
   EXPECT_FALSE(internal::CsmChannelTargetSelector("xds://authority/foo"));
 }
 
 TEST(CsmChannelTargetSelectorTest, XdsTargetsWithTDAuthority) {
+  auto obs = experimental::CsmObservabilityBuilder().BuildAndRegister();
   EXPECT_TRUE(internal::CsmChannelTargetSelector(
       "xds://traffic-director-global.xds.googleapis.com/foo"));
 }
 
+TEST(CsmChannelTargetSelectorTest, CsmObservabilityOutOfScope) {
+  { auto obs = experimental::CsmObservabilityBuilder().BuildAndRegister(); }
+  // When CsmObservability goes out of scope, the target selector should return
+  // false as well.
+  EXPECT_FALSE(internal::CsmChannelTargetSelector("foo.bar.google.com"));
+  EXPECT_FALSE(internal::CsmChannelTargetSelector("xds:///foo"));
+  EXPECT_FALSE(internal::CsmChannelTargetSelector(
+      "xds://traffic-director-global.xds.googleapis.com/foo"));
+}
+
+TEST(CsmServerSelectorTest, ChannelArgsWithoutXdsServerArg) {
+  auto obs = experimental::CsmObservabilityBuilder().BuildAndRegister();
+  EXPECT_FALSE(internal::CsmServerSelector(grpc_core::ChannelArgs()));
+}
+
+TEST(CsmServerSelectorTest, ChannelArgsWithXdsServerArg) {
+  auto obs = experimental::CsmObservabilityBuilder().BuildAndRegister();
+  EXPECT_TRUE(internal::CsmServerSelector(
+      grpc_core::ChannelArgs().Set(GRPC_ARG_XDS_ENABLED_SERVER, true)));
+}
+
+TEST(CsmServerSelectorTest, CsmObservabilityOutOfScope) {
+  { auto obs = experimental::CsmObservabilityBuilder().BuildAndRegister(); }
+  // When CsmObservability goes out of scope, the server selector should return
+  // false as well.
+  EXPECT_FALSE(internal::CsmServerSelector(grpc_core::ChannelArgs()));
+  EXPECT_FALSE(internal::CsmServerSelector(
+      grpc_core::ChannelArgs().Set(GRPC_ARG_XDS_ENABLED_SERVER, true)));
+}
+
 }  // namespace
 }  // namespace testing
 }  // namespace grpc