[XdsClient] add grpc.xds_client.server_failure metric (#36291)

As per gRFC A78 (https://github.com/grpc/proposal/pull/419).

Closes #36291

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36291 from markdroth:xds_client_counter a9363c2105
PiperOrigin-RevId: 623935691

src/core/ext/xds/xds_client.cc

@@ -641,6 +641,10 @@ void XdsClient::XdsChannel::SetChannelStatusLocked(absl::Status status) {
         absl::StrCat(status.message(),
                      " (node ID:", xds_client_->bootstrap_->node()->id(), ")"));
   }
+  // If status was previously OK, report that the channel has gone unhealthy.
+  if (status_.ok() && xds_client_->metrics_reporter_ != nullptr) {
+    xds_client_->metrics_reporter_->ReportServerFailure(server_.server_uri());
+  }
   // Save status in channel, so that we can immediately generate an
   // error for any new watchers that may be started.
   status_ = status;

src/core/ext/xds/xds_client_grpc.cc

@@ -114,11 +114,20 @@ const auto kMetricResourceUpdatesInvalid =
          kMetricLabelXdsResourceType},
         {}, false);
 
+const auto kMetricServerFailure =
+    GlobalInstrumentsRegistry::RegisterUInt64Counter(
+        "grpc.xds_client.server_failure",
+        "EXPERIMENTAL.  A counter of xDS servers going from healthy to "
+        "unhealthy.  A server goes unhealthy when we have a connectivity "
+        "failure or when the ADS stream fails without seeing a response "
+        "message, as per gRFC A57.",
+        "{failure}", {kMetricLabelTarget, kMetricLabelXdsServer}, {}, false);
+
 const auto kMetricConnected =
     GlobalInstrumentsRegistry::RegisterCallbackInt64Gauge(
         "grpc.xds_client.connected",
         "EXPERIMENTAL.  Whether or not the xDS client currently has a "
-        "working ADS stream to the xDS server. For a given server, this "
+        "working ADS stream to the xDS server.  For a given server, this "
         "will be set to 0 when we have a connectivity failure or when the "
         "ADS stream fails without seeing a response message, as per gRFC "
         "A57.  It will be set to 1 when we receive the first response on "
@@ -156,6 +165,11 @@ class GrpcXdsClient::MetricsReporter final : public XdsMetricsReporter {
         {xds_client_.key_, xds_server, resource_type}, {});
   }
 
+  void ReportServerFailure(absl::string_view xds_server) override {
+    xds_client_.stats_plugin_group_.AddCounter(
+        kMetricServerFailure, 1, {xds_client_.key_, xds_server}, {});
+  }
+
  private:
   GrpcXdsClient& xds_client_;
 };

src/core/ext/xds/xds_metrics.h

@@ -32,6 +32,8 @@ class XdsMetricsReporter {
                                      absl::string_view resource_type,
                                      uint64_t num_valid,
                                      uint64_t num_invalid) = 0;
+
+  virtual void ReportServerFailure(absl::string_view xds_server) = 0;
 };
 
 }  // namespace grpc_core

test/core/xds/xds_client_test.cc

@@ -625,6 +625,7 @@ class XdsClientTest : public ::testing::Test {
     using ResourceUpdateMap = std::map<
         std::pair<std::string /*xds_server*/, std::string /*resource_type*/>,
         uint64_t>;
+    using ServerFailureMap = std::map<std::string /*xds_server*/, uint64_t>;
 
     const ResourceUpdateMap& resource_updates_valid() const {
       return resource_updates_valid_;
@@ -632,6 +633,7 @@ class XdsClientTest : public ::testing::Test {
     const ResourceUpdateMap& resource_updates_invalid() const {
       return resource_updates_invalid_;
     }
+    const ServerFailureMap& server_failures() const { return server_failures_; }
 
    private:
     void ReportResourceUpdates(absl::string_view xds_server,
@@ -648,8 +650,13 @@ class XdsClientTest : public ::testing::Test {
       }
     }
 
+    void ReportServerFailure(absl::string_view xds_server) override {
+      ++server_failures_[std::string(xds_server)];
+    }
+
     ResourceUpdateMap resource_updates_valid_;
     ResourceUpdateMap resource_updates_invalid_;
+    ServerFailureMap server_failures_;
   };
 
   using ResourceCounts =
@@ -876,6 +883,7 @@ TEST_F(XdsClientTest, BasicWatch) {
               ::testing::ElementsAre());
   EXPECT_THAT(GetResourceCounts(), ::testing::ElementsAre());
   EXPECT_THAT(GetServerConnections(), ::testing::ElementsAre());
+  EXPECT_THAT(metrics_reporter_->server_failures(), ::testing::ElementsAre());
   // Start a watch for "foo1".
   auto watcher = StartFooWatch("foo1");
   // Check metrics.
@@ -2303,6 +2311,7 @@ TEST_F(XdsClientTest, StreamClosedByServerWithoutSeeingResponse) {
   // Check metric data.
   EXPECT_THAT(GetServerConnections(), ::testing::ElementsAre(::testing::Pair(
                                           kDefaultXdsServerUrl, true)));
+  EXPECT_THAT(metrics_reporter_->server_failures(), ::testing::ElementsAre());
   // Watcher should initially not see any resource reported.
   EXPECT_FALSE(watcher->HasEvent());
   // XdsClient should have created an ADS stream.
@@ -2321,6 +2330,8 @@ TEST_F(XdsClientTest, StreamClosedByServerWithoutSeeingResponse) {
   // Check metric data.
   EXPECT_THAT(GetServerConnections(), ::testing::ElementsAre(::testing::Pair(
                                           kDefaultXdsServerUrl, false)));
+  EXPECT_THAT(metrics_reporter_->server_failures(),
+              ::testing::ElementsAre(::testing::Pair(kDefaultXdsServerUrl, 1)));
   // XdsClient should report an error to the watcher.
   auto error = watcher->WaitForNextError();
   ASSERT_TRUE(error.has_value());
@@ -2344,6 +2355,8 @@ TEST_F(XdsClientTest, StreamClosedByServerWithoutSeeingResponse) {
   // Connection still reported as unhappy until we get a response.
   EXPECT_THAT(GetServerConnections(), ::testing::ElementsAre(::testing::Pair(
                                           kDefaultXdsServerUrl, false)));
+  EXPECT_THAT(metrics_reporter_->server_failures(),
+              ::testing::ElementsAre(::testing::Pair(kDefaultXdsServerUrl, 1)));
   // Server now sends the requested resource.
   stream->SendMessageToClient(
       ResponseBuilder(XdsFooResourceType::Get()->type_url())
@@ -2380,6 +2393,7 @@ TEST_F(XdsClientTest, ConnectionFails) {
   transport_factory_->SetAutoCompleteMessagesFromClient(false);
   // Metrics should initially be empty.
   EXPECT_THAT(GetServerConnections(), ::testing::ElementsAre());
+  EXPECT_THAT(metrics_reporter_->server_failures(), ::testing::ElementsAre());
   // Start a watch for "foo1".
   auto watcher = StartFooWatch("foo1");
   // Check metric data.
@@ -2412,6 +2426,8 @@ TEST_F(XdsClientTest, ConnectionFails) {
   // Connection reported as unhappy.
   EXPECT_THAT(GetServerConnections(), ::testing::ElementsAre(::testing::Pair(
                                           kDefaultXdsServerUrl, false)));
+  EXPECT_THAT(metrics_reporter_->server_failures(),
+              ::testing::ElementsAre(::testing::Pair(kDefaultXdsServerUrl, 1)));
   // We should not see a resource-does-not-exist event, because the
   // timer should not be running while the channel is disconnected.
   EXPECT_TRUE(watcher->ExpectNoEvent(absl::Seconds(4)));
@@ -3709,6 +3725,9 @@ TEST_F(XdsClientTest, FederationChannelFailureReportedToWatchers) {
               ::testing::ElementsAre(
                   ::testing::Pair(kDefaultXdsServerUrl, true),
                   ::testing::Pair(authority_server.server_uri(), false)));
+  EXPECT_THAT(metrics_reporter_->server_failures(),
+              ::testing::ElementsAre(
+                  ::testing::Pair(authority_server.server_uri(), 1)));
   // Cancel watch for "foo1".
   CancelFooWatch(watcher.get(), "foo1");
   EXPECT_TRUE(stream->Orphaned());
@@ -3821,6 +3840,7 @@ TEST_F(XdsClientTest, FallbackAndRecover) {
                   1)));
   EXPECT_THAT(metrics_reporter_->resource_updates_valid(),
               ::testing::IsEmpty());
+  EXPECT_THAT(metrics_reporter_->server_failures(), ::testing::ElementsAre());
   // XdsClient should have created an ADS stream.
   auto stream = WaitForAdsStream();
   ASSERT_TRUE(stream != nullptr);
@@ -3875,11 +3895,15 @@ TEST_F(XdsClientTest, FallbackAndRecover) {
   // Result (local): The metrics show the channel as being unhealthy.
   EXPECT_THAT(GetServerConnections(), ::testing::ElementsAre(::testing::Pair(
                                           kDefaultXdsServerUrl, false)));
+  EXPECT_THAT(metrics_reporter_->server_failures(),
+              ::testing::ElementsAre(::testing::Pair(kDefaultXdsServerUrl, 1)));
   // Input: Trigger stream failure.
   stream->MaybeSendStatusToClient(absl::UnavailableError("Stream failure"));
   // Result (local): The metrics still show the channel as being unhealthy.
   EXPECT_THAT(GetServerConnections(), ::testing::ElementsAre(::testing::Pair(
                                           kDefaultXdsServerUrl, false)));
+  EXPECT_THAT(metrics_reporter_->server_failures(),
+              ::testing::ElementsAre(::testing::Pair(kDefaultXdsServerUrl, 1)));
   // Result (remote): The client starts a new stream and sends a subscription
   //   message. Note that the server does not respond, so the channel will still
   //   have non-OK status.
@@ -3998,6 +4022,8 @@ TEST_F(XdsClientTest, FallbackAndRecover) {
                       2)));
   EXPECT_THAT(GetServerConnections(), ::testing::ElementsAre(::testing::Pair(
                                           kDefaultXdsServerUrl, true)));
+  EXPECT_THAT(metrics_reporter_->server_failures(),
+              ::testing::ElementsAre(::testing::Pair(kDefaultXdsServerUrl, 1)));
   // Result (remote): The stream to the fallback server has been orphaned.
   EXPECT_TRUE(stream2->Orphaned());
   // Result (local): Resources are delivered to watchers.
@@ -4053,6 +4079,8 @@ TEST_F(XdsClientTest, FallbackReportsError) {
               ::testing::ElementsAre(
                   ::testing::Pair(kDefaultXdsServerUrl, false),
                   ::testing::Pair(fallback_server.server_uri(), true)));
+  EXPECT_THAT(metrics_reporter_->server_failures(),
+              ::testing::ElementsAre(::testing::Pair(kDefaultXdsServerUrl, 1)));
   // Fallback happens now
   stream = WaitForAdsStream(fallback_server);
   ASSERT_NE(stream, nullptr);
@@ -4068,6 +4096,10 @@ TEST_F(XdsClientTest, FallbackReportsError) {
               ::testing::ElementsAre(
                   ::testing::Pair(kDefaultXdsServerUrl, false),
                   ::testing::Pair(fallback_server.server_uri(), false)));
+  EXPECT_THAT(
+      metrics_reporter_->server_failures(),
+      ::testing::ElementsAre(::testing::Pair(kDefaultXdsServerUrl, 1),
+                             ::testing::Pair(fallback_server.server_uri(), 1)));
   auto error = watcher->WaitForNextError();
   ASSERT_TRUE(error.has_value());
   EXPECT_THAT(error->code(), absl::StatusCode::kUnavailable);
@@ -4117,6 +4149,8 @@ TEST_F(XdsClientTest, FallbackOnStartup) {
               ::testing::ElementsAre(
                   ::testing::Pair(kDefaultXdsServerUrl, false),
                   ::testing::Pair(fallback_server.server_uri(), true)));
+  EXPECT_THAT(metrics_reporter_->server_failures(),
+              ::testing::ElementsAre(::testing::Pair(kDefaultXdsServerUrl, 1)));
   // XdsClient should have delivered the response to the watcher.
   auto resource = watcher->WaitForNextResource();
   ASSERT_NE(resource, nullptr);

test/cpp/end2end/xds/xds_core_end2end_test.cc

@@ -1130,6 +1130,23 @@ TEST_P(XdsMetricsTest, MetricDefinitionResourceUpdatesInvalid) {
   EXPECT_THAT(descriptor->optional_label_keys, ::testing::ElementsAre());
 }
 
+TEST_P(XdsMetricsTest, MetricDefinitionServerFailure) {
+  const auto* descriptor =
+      grpc_core::GlobalInstrumentsRegistryTestPeer::FindMetricDescriptorByName(
+          "grpc.xds_client.server_failure");
+  ASSERT_NE(descriptor, nullptr);
+  EXPECT_EQ(descriptor->value_type,
+            grpc_core::GlobalInstrumentsRegistry::ValueType::kUInt64);
+  EXPECT_EQ(descriptor->instrument_type,
+            grpc_core::GlobalInstrumentsRegistry::InstrumentType::kCounter);
+  EXPECT_EQ(descriptor->enable_by_default, false);
+  EXPECT_EQ(descriptor->name, "grpc.xds_client.server_failure");
+  EXPECT_EQ(descriptor->unit, "{failure}");
+  EXPECT_THAT(descriptor->label_keys,
+              ::testing::ElementsAre("grpc.target", "grpc.xds.server"));
+  EXPECT_THAT(descriptor->optional_label_keys, ::testing::ElementsAre());
+}
+
 TEST_P(XdsMetricsTest, MetricDefinitionConnected) {
   const auto* descriptor =
       grpc_core::GlobalInstrumentsRegistryTestPeer::FindMetricDescriptorByName(
@@ -1179,6 +1196,10 @@ TEST_P(XdsMetricsTest, MetricValues) {
           FindUInt64CounterHandleByName(
               "grpc.xds_client.resource_updates_invalid")
               .value();
+  const auto kMetricServerFailure =
+      grpc_core::GlobalInstrumentsRegistryTestPeer::
+          FindUInt64CounterHandleByName("grpc.xds_client.server_failure")
+              .value();
   const auto kMetricConnected =
       grpc_core::GlobalInstrumentsRegistryTestPeer::
           FindCallbackInt64GaugeHandleByName("grpc.xds_client.connected")
@@ -1199,6 +1220,9 @@ TEST_P(XdsMetricsTest, MetricValues) {
   EXPECT_THAT(stats_plugin_->GetCallbackGaugeValue(kMetricConnected,
                                                    {kTarget, kXdsServer}, {}),
               ::testing::Optional(1));
+  EXPECT_THAT(stats_plugin_->GetCounterValue(kMetricServerFailure,
+                                             {kTarget, kXdsServer}, {}),
+              absl::nullopt);
   for (absl::string_view type_url :
        {"envoy.config.listener.v3.Listener",
         "envoy.config.route.v3.RouteConfiguration",
@@ -1220,6 +1244,9 @@ TEST_P(XdsMetricsTest, MetricValues) {
   EXPECT_THAT(stats_plugin_->GetCallbackGaugeValue(kMetricConnected,
                                                    {"#server", kXdsServer}, {}),
               ::testing::Optional(1));
+  EXPECT_THAT(stats_plugin_->GetCounterValue(kMetricServerFailure,
+                                             {"#server", kXdsServer}, {}),
+              absl::nullopt);
   for (absl::string_view type_url :
        {"envoy.config.listener.v3.Listener",
         "envoy.config.route.v3.RouteConfiguration"}) {
@@ -1236,6 +1263,26 @@ TEST_P(XdsMetricsTest, MetricValues) {
             kMetricResources, {"#server", "#old", type_url, "acked"}, {}),
         ::testing::Optional(1));
   }
+  // Shut down balancer and wait for metrics to show the failure.
+  balancer_->Shutdown();
+  for (const char* target : {kTarget.c_str(), "#server"}) {
+    const absl::Time deadline =
+        absl::Now() + absl::Seconds(5 * grpc_test_slowdown_factor());
+    while (true) {
+      auto value = stats_plugin_->GetCounterValue(kMetricServerFailure,
+                                                  {target, kXdsServer}, {});
+      if (value.has_value()) {
+        EXPECT_EQ(1, *value);
+        break;
+      }
+      ASSERT_LE(absl::Now(), deadline);
+      absl::SleepFor(absl::Seconds(1));
+    }
+    stats_plugin_->TriggerCallbacks();
+    EXPECT_THAT(stats_plugin_->GetCallbackGaugeValue(kMetricConnected,
+                                                     {target, kXdsServer}, {}),
+                ::testing::Optional(0));
+  }
 }
 
 //