internal/telemetry: add gRPC transport for OTLP trace export

The OTLP specification defines two transports: HTTP (port 4318) and gRPC
(port 4317). The existing exporter setup only supports HTTP/HTTPS schemes.
This adds gRPC support via URL scheme dispatch:

  - grpc://host:port  → plaintext gRPC
  - grpcs://host:port → TLS-secured gRPC

Many observability backends (Jaeger, Tempo, Datadog) prefer gRPC for its
lower overhead. Both otlptracehttp and otlptracegrpc return the same
*otlptrace.Exporter type, so only the exporter construction changes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cmd/utils/flags.go

@@ -1063,19 +1063,19 @@ Please note that --` + MetricsHTTPFlag.Name + ` must be set to start the server.
 
 	RPCTelemetryEndpointFlag = &cli.StringFlag{
 		Name:     "rpc.telemetry.endpoint",
-		Usage:    "Defines where RPC telemetry is sent (e.g., http://localhost:4318)",
+		Usage:    "Defines where RPC telemetry is sent (e.g., http://localhost:4318 or grpc://localhost:4317)",
 		Category: flags.APICategory,
 	}
 
 	RPCTelemetryUserFlag = &cli.StringFlag{
 		Name:     "rpc.telemetry.username",
-		Usage:    "HTTP Basic Auth username for OpenTelemetry",
+		Usage:    "Basic Auth username for OpenTelemetry",
 		Category: flags.APICategory,
 	}
 
 	RPCTelemetryPasswordFlag = &cli.StringFlag{
 		Name:     "rpc.telemetry.password",
-		Usage:    "HTTP Basic Auth password for OpenTelemetry",
+		Usage:    "Basic Auth password for OpenTelemetry",
 		Category: flags.APICategory,
 	}
 

go.mod

@@ -63,6 +63,7 @@ require (
 	github.com/urfave/cli/v2 v2.27.5
 	go.opentelemetry.io/otel v1.40.0
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.39.0
+	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.39.0
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.39.0
 	go.opentelemetry.io/otel/sdk v1.40.0
 	go.opentelemetry.io/otel/trace v1.40.0

go.sum

@@ -384,6 +384,8 @@ go.opentelemetry.io/otel v1.40.0 h1:oA5YeOcpRTXq6NN7frwmwFR0Cn3RhTVZvXsP4duvCms=
 go.opentelemetry.io/otel v1.40.0/go.mod h1:IMb+uXZUKkMXdPddhwAHm6UfOwJyh4ct1ybIlV14J0g=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.39.0 h1:f0cb2XPmrqn4XMy9PNliTgRKJgS5WcL/u0/WRYGz4t0=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.39.0/go.mod h1:vnakAaFckOMiMtOIhFI2MNH4FYrZzXCYxmb1LlhoGz8=
+go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.39.0 h1:in9O8ESIOlwJAEGTkkf34DesGRAc/Pn8qJ7k3r/42LM=
+go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.39.0/go.mod h1:Rp0EXBm5tfnv0WL+ARyO/PHBEaEAT8UUHQ6AGJcSq6c=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.39.0 h1:Ckwye2FpXkYgiHX7fyVrN1uA/UYd9ounqqTuSNAv0k4=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.39.0/go.mod h1:teIFJh5pW2y+AN7riv6IBPX2DuesS3HgP39mwOspKwU=
 go.opentelemetry.io/otel/metric v1.40.0 h1:rcZe317KPftE2rstWIBitCdVp89A2HqjkxR3c11+p9g=

internal/telemetry/tracesetup/setup.go

@@ -30,6 +30,7 @@ import (
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/exporters/otlp/otlptrace"
+	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
 	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp"
 	"go.opentelemetry.io/otel/propagation"
 	"go.opentelemetry.io/otel/sdk/resource"
@@ -101,6 +102,19 @@ func SetupTelemetry(cfg node.OpenTelemetryConfig, stack *node.Node) error {
 			}))
 		}
 		exporter = otlptracehttp.NewUnstarted(opts...)
+	case "grpc", "grpcs":
+		opts := []otlptracegrpc.Option{
+			otlptracegrpc.WithEndpoint(u.Host),
+		}
+		if u.Scheme == "grpc" {
+			opts = append(opts, otlptracegrpc.WithInsecure())
+		}
+		if cfg.AuthUser != "" {
+			opts = append(opts, otlptracegrpc.WithHeaders(map[string]string{
+				"Authorization": "Basic " + base64.StdEncoding.EncodeToString([]byte(cfg.AuthUser+":"+cfg.AuthPassword)),
+			}))
+		}
+		exporter = otlptracegrpc.NewUnstarted(opts...)
 	default:
 		return fmt.Errorf("unsupported telemetry url scheme: %s", u.Scheme)
 	}