snapshot of https://github.com/grpc/grpc-go.git (master, 2026-09-15; blobs > 131072B omitted)

examples/features/health/README.md

@@ -0,0 +1,74 @@
+# Health
+
+gRPC provides a health library to communicate a system's health to their
+clients. It works by providing a service definition via the
+[health/v1](https://github.com/grpc/grpc-proto/blob/master/grpc/health/v1/health.proto)
+api.
+
+Clients use the health library to gracefully avoid servers that encounter
+issues. Most languages provide an out-of-box implementation, which makes it
+interoperable between systems.
+
+## Try it
+
+```
+go run server/main.go -port=50051 -sleep=5s
+go run server/main.go -port=50052 -sleep=10s
+```
+
+```
+go run client/main.go
+```
+
+## Explanation
+
+### Client
+
+Clients have two ways to monitor a server's health. They use `Check()` to probe
+a server's health or `Watch()` to observe changes.
+
+In most cases, clients do not directly check backend servers. Instead, they do
+this transparently when you specify a `healthCheckConfig` in the [service
+config](https://github.com/grpc/proposal/blob/master/A17-client-side-health-checking.md#service-config-changes)
+and import the [health
+package](https://pkg.go.dev/google.golang.org/grpc/health). The `serviceName` in
+`healthCheckConfig` is used in the health check when connections are
+established. An empty string (`""`) typically indicates the overall health of a
+server.
+
+```go
+// import grpc/health to enable transparent client side checking
+import _ "google.golang.org/grpc/health"
+
+serviceConfig := grpc.WithDefaultServiceConfig(`{
+  "loadBalancingPolicy": "round_robin",
+  "healthCheckConfig": {
+    "serviceName": ""
+  }
+}`)
+
+conn, err := grpc.NewClient(..., serviceConfig)
+```
+
+See [A17 - Client-Side Health
+Checking](https://github.com/grpc/proposal/blob/master/A17-client-side-health-checking.md)
+for more details.
+
+### Server
+
+Servers control their serving status. They do this by inspecting dependent
+systems, then update their status accordingly. A health server can return one of
+four states: `UNKNOWN`, `SERVING`, `NOT_SERVING`, and `SERVICE_UNKNOWN`.
+
+`UNKNOWN` indicates the system does not yet know the current state. Servers
+often show this state at startup.
+
+`SERVING` means that the system is healthy and ready to service requests.
+Conversely, `NOT_SERVING` indicates the system is unable to service requests at
+the time.
+
+`SERVICE_UNKNOWN` communicates the `serviceName` requested by the client is not
+known by the server. This status is only reported by the `Watch()` call.
+
+A server may toggle its health using
+`healthServer.SetServingStatus("serviceName", servingStatus)`.

examples/features/health/client/main.go

@@ -0,0 +1,88 @@
+/*
+ *
+ * Copyright 2020 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.
+ *
+ */
+
+// Binary client demonstrates how to check and observe gRPC server health using
+// the health library.
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"time"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+	pb "google.golang.org/grpc/examples/features/proto/echo"
+	_ "google.golang.org/grpc/health" // REQUIRED to enable health checks
+	"google.golang.org/grpc/resolver"
+	"google.golang.org/grpc/resolver/manual"
+)
+
+const serviceConfig = `{
+	"loadBalancingPolicy": "round_robin",
+	"healthCheckConfig": {
+		"serviceName": ""
+	}
+}`
+
+func callUnaryEcho(c pb.EchoClient) {
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+	r, err := c.UnaryEcho(ctx, &pb.EchoRequest{})
+	if err != nil {
+		fmt.Println("UnaryEcho: _, ", err)
+	} else {
+		fmt.Println("UnaryEcho: ", r.GetMessage())
+	}
+}
+
+func main() {
+	flag.Parse()
+
+	r := manual.NewBuilderWithScheme("whatever")
+	r.InitialState(resolver.State{
+		Addresses: []resolver.Address{
+			{Addr: "localhost:50051"},
+			{Addr: "localhost:50052"},
+		},
+	})
+
+	address := fmt.Sprintf("%s:///unused", r.Scheme())
+
+	options := []grpc.DialOption{
+		grpc.WithTransportCredentials(insecure.NewCredentials()),
+		grpc.WithResolvers(r),
+		// google.golang.org/grpc/health must also be imported
+		grpc.WithDefaultServiceConfig(serviceConfig),
+	}
+
+	conn, err := grpc.NewClient(address, options...)
+	if err != nil {
+		log.Fatalf("grpc.NewClient(%q): %v", address, err)
+	}
+	defer conn.Close()
+
+	echoClient := pb.NewEchoClient(conn)
+
+	for {
+		callUnaryEcho(echoClient)
+		time.Sleep(time.Second)
+	}
+}

examples/features/health/server/main.go

@@ -0,0 +1,90 @@
+/*
+ *
+ * Copyright 2020 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.
+ *
+ */
+
+// Binary server demonstrates how to manage and report its health status using
+// the gRPC health library.
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"time"
+
+	"google.golang.org/grpc"
+	pb "google.golang.org/grpc/examples/features/proto/echo"
+	"google.golang.org/grpc/health"
+	healthgrpc "google.golang.org/grpc/health/grpc_health_v1"
+	healthpb "google.golang.org/grpc/health/grpc_health_v1"
+)
+
+var (
+	port  = flag.Int("port", 50051, "the port to serve on")
+	sleep = flag.Duration("sleep", time.Second*5, "duration between changes in health")
+
+	system = "" // empty string represents the health of the system
+)
+
+type echoServer struct {
+	pb.UnimplementedEchoServer
+}
+
+func (e *echoServer) UnaryEcho(context.Context, *pb.EchoRequest) (*pb.EchoResponse, error) {
+	return &pb.EchoResponse{
+		Message: fmt.Sprintf("hello from localhost:%d", *port),
+	}, nil
+}
+
+var _ pb.EchoServer = &echoServer{}
+
+func main() {
+	flag.Parse()
+
+	lis, err := net.Listen("tcp", fmt.Sprintf(":%d", *port))
+	if err != nil {
+		log.Fatalf("failed to listen: %v", err)
+	}
+
+	s := grpc.NewServer()
+	healthcheck := health.NewServer()
+	healthgrpc.RegisterHealthServer(s, healthcheck)
+	pb.RegisterEchoServer(s, &echoServer{})
+
+	go func() {
+		// asynchronously inspect dependencies and toggle serving status as needed
+		next := healthpb.HealthCheckResponse_SERVING
+
+		for {
+			healthcheck.SetServingStatus(system, next)
+
+			if next == healthpb.HealthCheckResponse_SERVING {
+				next = healthpb.HealthCheckResponse_NOT_SERVING
+			} else {
+				next = healthpb.HealthCheckResponse_SERVING
+			}
+
+			time.Sleep(*sleep)
+		}
+	}()
+
+	if err := s.Serve(lis); err != nil {
+		log.Fatalf("failed to serve: %v", err)
+	}
+}