grpc

gRPC Example

This example demonstrates gRPC server and client functionality.

Features

• gRPC Server with reflection enabled
• gRPC Client for calling external services
• Proto file configuration
• TLS/mTLS support (commented examples)
• Data enrichment from external gRPC services

Files

• config.hcl - Complete configuration with server, client, and flows

Usage

# Start the service
mycel start --config ./examples/grpc

# Test with grpcurl (requires reflection enabled)
grpcurl -plaintext localhost:50051 list
grpcurl -plaintext localhost:50051 UserService/ListUsers
grpcurl -plaintext -d '{"id": "1"}' localhost:50051 UserService/GetUser

Configuration

Server

connector "grpc_api" {
  type   = "grpc"
  driver = "server"
  port   = 50051

  proto_path = "./protos"
  reflection = true
}

Client

connector "user_service" {
  type       = "grpc"
  driver     = "client"
  target     = "user-service:50051"
  proto_path = "./protos"
  insecure   = true
}

Flow Operations

Operations use the format ServiceName/MethodName:

flow "get_user" {
  from {
    connector = "grpc_api"
    operation = "UserService/GetUser"
  }
  # ...
}

Verify It Works

1. Start the service

mycel start --config ./examples/grpc

You should see:

INFO  Starting service: grpc-example
INFO  Loaded 2 connectors: grpc_api, database
INFO  gRPC server listening on :50051
INFO  gRPC reflection enabled

2. List available services

grpcurl -plaintext localhost:50051 list

Expected output:

UserService
grpc.reflection.v1alpha.ServerReflection

3. Describe a service

grpcurl -plaintext localhost:50051 describe UserService

Expected output:

UserService is a service:
service UserService {
  rpc CreateUser ( CreateUserRequest ) returns ( User );
  rpc GetUser ( GetUserRequest ) returns ( User );
  rpc ListUsers ( Empty ) returns ( UserList );
}

4. List users (empty initially)

grpcurl -plaintext localhost:50051 UserService/ListUsers

Expected output:

{
  "users": []
}

5. Create a user

grpcurl -plaintext -d '{"email": "test@example.com", "name": "Test User"}' \
  localhost:50051 UserService/CreateUser

Expected output:

{
  "id": "<uuid>",
  "email": "test@example.com",
  "name": "Test User"
}

What to check in logs

INFO  gRPC request: UserService/ListUsers
INFO    Flow: list_users → database:users
INFO  gRPC response sent in 2ms

Common Issues

"grpcurl: command not found"

Install grpcurl:

# macOS
brew install grpcurl

# Linux
go install github.com/fullstorydev/grpcurl/cmd/grpcurl@latest

"Failed to dial: connection refused"

The gRPC server is not running. Check if port 50051 is in use:

lsof -i :50051

"Server does not support reflection"

Ensure reflection = true is set in the gRPC connector config.

"Proto file not found"

Check that proto_path points to a valid directory with .proto files.

See Also

• TCP Example - Alternative to gRPC for simpler protocols