Reflection

Hub › gRPC › Advanced › Reflection

Goal

Enable gRPC reflection so tools like grpcurl can discover services and call RPCs without the proto file.

Prerequisites

• Health checking

Why reflection

Without reflection, a gRPC client (or CLI tool) needs the .proto file to know the service definition. Reflection lets clients discover:

• Available services and methods
• Message types and fields
• Serialized wire format

This is essential for debugging, monitoring, and generic gRPC clients.

Enable reflection

import { ReflectionService } from '@grpc/reflection';

const reflection = new ReflectionService(packageDef);
reflection.addToServer(server);

Add before server.bindAsync.

Using grpcurl

# Install grpcurl
brew install grpcurl

# List services
grpcurl -plaintext localhost:50051 list
# chat.ChatService
# grpc.health.v1.Health
# grpc.reflection.v1.ServerReflection

# Describe service
grpcurl -plaintext localhost:50051 describe chat.ChatService

# Call an RPC
echo '{"user":"alice","text":"hello"}' | \
  grpcurl -plaintext -d @ localhost:50051 chat.ChatService/Chat

# Describe message type
grpcurl -plaintext localhost:50051 describe chat.ChatMessage
# chat.ChatMessage is a message:
#     string user (1)
#     string text (2)

grpcurl with TLS

grpcurl -cacert ca-cert.pem -cert client-cert.pem -key client-key.pem \
  localhost:50051 list

Checkpoint

grpcurl -plaintext localhost:50051 list
# chat.ChatService
# grpc.health.v1.Health

Next: Load balancing — round-robin across server replicas.