[examples] Implement custom metrics reporting from server

examples/cpp/cmake/common.cmake

@@ -51,6 +51,7 @@ if(GRPC_AS_SUBMODULE)
   # this build.
   set(_PROTOBUF_LIBPROTOBUF libprotobuf)
   set(_REFLECTION grpc++_reflection)
+  set(_ORCA_SERVICE grpcpp_orca_service)
   if(CMAKE_CROSSCOMPILING)
     find_program(_PROTOBUF_PROTOC protoc)
   else()

examples/cpp/orca/BUILD

@@ -0,0 +1,29 @@
+# Copyright 2023 the gRPC authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+licenses(["notice"])
+
+cc_binary(
+    name = "orca_server",
+    srcs = ["orca_server.cc"],
+    defines = ["BAZEL_BUILD"],
+    deps = [
+        "//:grpc++",
+        "//:grpcpp_orca_service",
+        "//examples/protos:helloworld_cc_grpc",
+        "@com_google_absl//absl/flags:flag",
+        "@com_google_absl//absl/flags:parse",
+        "@com_google_absl//absl/strings:str_format",
+    ],
+)

examples/cpp/orca/README.md

@@ -0,0 +1,46 @@
+# gRPC Custom Metrics Example
+
+You can find a complete set of instructions for building gRPC and running the
+examples in the [C++ Quick Start][].
+
+This example shows how to implement a server that provides custom metrics usable
+by custom load balancing policies.
+
+Server needs to be setup with metrics recorder and Orca service for sending
+these metrics to a client:
+
+```c++
+GreeterServiceImpl service;
+// Setup custom metrics recording
+auto server_metric_recorder =
+    grpc::experimental::ServerMetricRecorder::Create();
+grpc::experimental::OrcaService orca_service(
+    server_metric_recorder.get(),
+    grpc::experimental::OrcaService::Options().set_min_report_duration(
+        absl::Seconds(0.1)));
+builder.RegisterService(&orca_service);
+grpc::ServerBuilder::experimental_type(&builder).EnableCallMetricRecording(
+    nullptr);
+```
+
+Afterwards per-request metrics can be reported from the gRPC service
+implementation using the metric recorder from the request context:
+
+```c++
+auto recorder = context->ExperimentalGetCallMetricRecorder();
+if (recorder == nullptr) {
+  return Status(grpc::StatusCode::INTERNAL,
+                "Unable to access metrics recorder. Make sure "
+                "EnableCallMetricRecording had been called.");
+}
+recorder->RecordCpuUtilizationMetric(0.5);
+```
+
+Out of band metrics can be reported using the `server_metric_recorder`
+directly:
+
+```c++
+server_metric_recorder->SetCpuUtilization(0.75);
+```
+
+[C++ Quick Start]: https://grpc.io/docs/languages/cpp/quickstart

examples/cpp/orca/orca_server.cc

@@ -0,0 +1,96 @@
+/*
+ *
+ * Copyright 2023 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+#include <cstddef>
+#include <iostream>
+#include <memory>
+#include <string>
+
+#include "absl/flags/flag.h"
+#include "absl/flags/parse.h"
+#include "absl/strings/str_format.h"
+#include "examples/protos/helloworld.grpc.pb.h"
+
+#include <grpcpp/ext/call_metric_recorder.h>
+#include <grpcpp/ext/orca_service.h>
+#include <grpcpp/grpcpp.h>
+#include <grpcpp/health_check_service_interface.h>
+#include <grpcpp/support/status.h>
+
+using grpc::Server;
+using grpc::ServerBuilder;
+using grpc::ServerContext;
+using grpc::Status;
+using helloworld::Greeter;
+using helloworld::HelloReply;
+using helloworld::HelloRequest;
+
+ABSL_FLAG(uint16_t, port, 50051, "Server port for the service");
+
+// Logic and data behind the server's behavior.
+class GreeterServiceImpl final : public Greeter::Service {
+  Status SayHello(ServerContext* context, const HelloRequest* request,
+                  HelloReply* reply) override {
+    auto recorder = context->ExperimentalGetCallMetricRecorder();
+    if (recorder == nullptr) {
+      return Status(grpc::StatusCode::INTERNAL,
+                    "Unable to access metrics recorder. Make sure "
+                    "EnableCallMetricRecording had been called.");
+    }
+    recorder->RecordRequestCostMetric("db_queries", 10);
+    recorder->RecordCpuUtilizationMetric(0.5);
+    std::string prefix("Hello ");
+    reply->set_message(prefix + request->name());
+    return Status::OK;
+  }
+};
+
+void RunServer(uint16_t port) {
+  std::string server_address = absl::StrFormat("0.0.0.0:%d", port);
+  ServerBuilder builder;
+  GreeterServiceImpl service;
+  // Setup custom metrics recording
+  auto server_metric_recorder =
+      grpc::experimental::ServerMetricRecorder::Create();
+  grpc::experimental::OrcaService orca_service(
+      server_metric_recorder.get(),
+      grpc::experimental::OrcaService::Options().set_min_report_duration(
+          absl::Seconds(0.1)));
+  builder.RegisterService(&orca_service);
+  grpc::ServerBuilder::experimental_type(&builder).EnableCallMetricRecording(
+      server_metric_recorder.get());
+  // Resume setting up gRPC server as usual
+  grpc::EnableDefaultHealthCheckService(true);
+  // Listen on the given address without any authentication mechanism.
+  builder.AddListeningPort(server_address, grpc::InsecureServerCredentials());
+  // Register "service" as the instance through which we'll communicate with
+  // clients. In this case it corresponds to an *synchronous* service.
+  builder.RegisterService(&service);
+  // Finally assemble the server.
+  std::unique_ptr<Server> server(builder.BuildAndStart());
+  std::cout << "Server listening on " << server_address << std::endl;
+
+  // Wait for the server to shutdown. Note that some other thread must be
+  // responsible for shutting down the server for this call to ever return.
+  server->Wait();
+}
+
+int main(int argc, char** argv) {
+  absl::ParseCommandLine(argc, argv);
+  RunServer(absl::GetFlag(FLAGS_port));
+  return 0;
+}