feat(admin): add otelgrpc metric interceptor

This change adds a new gRPC interceptor, pkg/rpc/interceptors/otelgrpc. Currently, it only supports
UnaryServerInterceptor.
It follows [OTel 1.22.0 specification](https://opentelemetry.io/docs/specs/otel/metrics/semantic_conventions/rpc-metrics/)
except for the unit of rpc.server.duration, which converts from milliseconds to microseconds for
high resolution.

internal/admin/admin.go

@@ -19,8 +19,10 @@ import (
 
 	"github.com/kakao/varlog/internal/admin/snwatcher"
 	"github.com/kakao/varlog/pkg/rpc/interceptors/logging"
+	"github.com/kakao/varlog/pkg/rpc/interceptors/otelgrpc"
 	"github.com/kakao/varlog/pkg/types"
 	"github.com/kakao/varlog/pkg/util/netutil"
+	"github.com/kakao/varlog/pkg/util/telemetry"
 	"github.com/kakao/varlog/pkg/verrors"
 	"github.com/kakao/varlog/proto/admpb"
 	"github.com/kakao/varlog/proto/mrpb"
@@ -72,6 +74,7 @@ func New(ctx context.Context, opts ...Option) (*Admin, error) {
 	grpcServer := grpc.NewServer(
 		grpc.ChainUnaryInterceptor(
 			logging.UnaryServerInterceptor(cfg.logger),
+			otelgrpc.UnaryServerInterceptor(telemetry.GetGlobalMeterProvider()),
 		),
 	)
 

pkg/rpc/interceptors/context.go

@@ -0,0 +1,46 @@
+package interceptors
+
+import (
+	"context"
+	"net"
+	"strings"
+
+	"google.golang.org/grpc/peer"
+)
+
+func PeerAddress(ctx context.Context) string {
+	p, ok := peer.FromContext(ctx)
+	if !ok {
+		return ""
+	}
+
+	host, _, err := net.SplitHostPort(p.Addr.String())
+	if err != nil {
+		return ""
+	}
+
+	if host == "" {
+		return "127.0.0.1"
+	}
+	return host
+}
+
+// ParseFullMethod returns service and method extracted from gRPC full method
+// string, i.e., /package.service/method.
+func ParseFullMethod(fullMethod string) (service, method string) {
+	name, found := strings.CutPrefix(fullMethod, "/")
+	if !found {
+		// Invalid format, does not follow `/package.service/method`.
+		return "", ""
+	}
+	service, method, found = strings.Cut(name, "/")
+	if !found {
+		// Invalid format, does not follow `/package.service/method`.
+		return "", ""
+	}
+	if strings.Contains(method, "/") {
+		// Invalid format, does not follow `/package.service/method`.
+		return "", ""
+	}
+	return service, method
+}

pkg/rpc/interceptors/context_test.go

@@ -0,0 +1,55 @@
+package interceptors
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestParseFullMethod(t *testing.T) {
+	tcs := []struct {
+		fullMethod string
+		service    string
+		method     string
+	}{
+		{
+			fullMethod: "/varlog.admpb.ClusterManager/ListStorageNodes",
+			service:    "varlog.admpb.ClusterManager",
+			method:     "ListStorageNodes",
+		},
+		{
+			fullMethod: "varlog.admpb.ClusterManager/OuterMethod/InnerMethod",
+			service:    "",
+			method:     "",
+		},
+		{
+			fullMethod: "/varlog.admpb.ClusterManager/OuterMethod/InnerMethod",
+			service:    "",
+			method:     "",
+		},
+		{
+			fullMethod: "varlog.admpb.ClusterManager/ListStorageNodes",
+			service:    "",
+			method:     "",
+		},
+		{
+			fullMethod: "/varlog.admpb.ClusterManager",
+			service:    "",
+			method:     "",
+		},
+		{
+			fullMethod: "ListStorageNodes",
+			service:    "",
+			method:     "",
+		},
+	}
+
+	for _, tc := range tcs {
+		tc := tc
+		t.Run(tc.fullMethod, func(t *testing.T) {
+			service, method := ParseFullMethod(tc.fullMethod)
+			require.Equal(t, tc.service, service)
+			require.Equal(t, tc.method, method)
+		})
+	}
+}

pkg/rpc/interceptors/logging/interceptor.go

@@ -3,13 +3,13 @@ package logging
 import (
 	"context"
 	"fmt"
-	"net"
 	"time"
 
 	"go.uber.org/zap"
 	"google.golang.org/grpc"
-	"google.golang.org/grpc/peer"
 	"google.golang.org/grpc/status"
+
+	"github.com/kakao/varlog/pkg/rpc/interceptors"
 )
 
 // UnaryServerInterceptor returns a new unary server interceptor that logs a
@@ -31,27 +31,10 @@ func UnaryServerInterceptor(logger *zap.Logger) grpc.UnaryServerInterceptor {
 				zap.Duration("duration", duration),
 				zap.Stringer("request", req.(fmt.Stringer)),
 				zap.Stringer("response", resp.(fmt.Stringer)),
-				zap.String("peer", peerAddr(ctx)),
+				zap.String("peer", interceptors.PeerAddress(ctx)),
 				zap.Error(err),
 			)
 		}
 		return resp, err
 	}
 }
-
-func peerAddr(ctx context.Context) string {
-	p, ok := peer.FromContext(ctx)
-	if !ok {
-		return ""
-	}
-
-	host, _, err := net.SplitHostPort(p.Addr.String())
-	if err != nil {
-		return ""
-	}
-
-	if host == "" {
-		return "127.0.0.1"
-	}
-	return host
-}

pkg/rpc/interceptors/otelgrpc/interceptor.go

@@ -0,0 +1,66 @@
+package otelgrpc
+
+import (
+	"context"
+	"time"
+
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/metric"
+	semconv "go.opentelemetry.io/otel/semconv/v1.20.0"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+
+	"github.com/kakao/varlog/pkg/rpc/interceptors"
+)
+
+const (
+	instrumentationName = "github.com/kakao/varlog/pkg/rpc/interceptors/otelgrpc"
+)
+
+// UnaryServerInterceptor returns a new unary server interceptor that records
+// OpenTelemetry metrics for gRPC.
+// It follows [OTel 1.22.0](https://opentelemetry.io/docs/specs/otel/metrics/semantic_conventions/rpc-metrics/)
+// specification except for the unit of rpc.server.duration, which converts
+// from milliseconds to microseconds for high resolution.
+func UnaryServerInterceptor(meterProvider metric.MeterProvider) grpc.UnaryServerInterceptor {
+	meter := meterProvider.Meter(
+		instrumentationName,
+		metric.WithSchemaURL(semconv.SchemaURL),
+	)
+	rpcServerDuration, err := meter.Int64Histogram(
+		"rpc.server.duration",
+		metric.WithDescription("measures duration of inbound RPC in microseconds"),
+		metric.WithUnit("us"),
+	)
+	if err != nil {
+		otel.Handle(err)
+	}
+
+	return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (resp interface{}, err error) {
+		code := codes.OK
+
+		defer func(start time.Time) {
+			elapsedTime := time.Since(start) / time.Microsecond
+
+			attrs := make([]attribute.KeyValue, 0, 4)
+			attrs = append(attrs, semconv.RPCSystemGRPC, semconv.RPCGRPCStatusCodeKey.Int64(int64(code)))
+			service, method := interceptors.ParseFullMethod(info.FullMethod)
+			if service != "" {
+				attrs = append(attrs, semconv.RPCServiceKey.String(service))
+			}
+			if method != "" {
+				attrs = append(attrs, semconv.RPCMethodKey.String(method))
+			}
+
+			rpcServerDuration.Record(ctx, int64(elapsedTime), metric.WithAttributes(attrs...))
+		}(time.Now())
+
+		resp, err = handler(ctx, req)
+		if err != nil {
+			code = status.Code(err)
+		}
+		return resp, err
+	}
+}