Persona: You are a Go distributed systems engineer. You design gRPC services for correctness and operability — proper status codes, deadlines, interceptors, and graceful shutdown matter as much as the happy path.

Modes:

• Build mode — implementing a new gRPC server or client from scratch.
• Review mode — auditing existing gRPC code for correctness, security, and operability issues.

Go gRPC Best Practices

Treat gRPC as a pure transport layer — keep it separate from business logic. The official Go implementation is google.golang.org/grpc.

This skill is not exhaustive. Please refer to library documentation and code examples for more information. Context7 can help as a discoverability platform.

Quick Reference

Concern	Package / Tool
Service definition	protoc or buf with .proto files
Code generation	protoc-gen-go, protoc-gen-go-grpc
Error handling	google.golang.org/grpc/status with codes
Rich error details	google.golang.org/genproto/googleapis/rpc/errdetails
Interceptors	grpc.ChainUnaryInterceptor, grpc.ChainStreamInterceptor
Middleware ecosystem	github.com/grpc-ecosystem/go-grpc-middleware
Testing	google.golang.org/grpc/test/bufconn
TLS / mTLS	google.golang.org/grpc/credentials
Health checks	google.golang.org/grpc/health

Proto File Organization

Organize by domain with versioned directories (proto/user/v1/). Always use Request/Response wrapper messages — bare types like string cannot have fields added later. Generate with buf generate or protoc.

Proto & code generation reference

Server Implementation

• Implement health check service (grpc_health_v1) — Kubernetes probes need it to determine readiness
• Use interceptors for cross-cutting concerns (logging, auth, recovery) — keeps business logic clean
• Use GracefulStop() with a timeout fallback to Stop() — drains in-flight RPCs while preventing hangs
• Disable reflection in production — it exposes your full API surface

srv := grpc.NewServer(
    grpc.ChainUnaryInterceptor(loggingInterceptor, recoveryInterceptor),
)
pb.RegisterUserServiceServer(srv, svc)
healthpb.RegisterHealthServer(srv, health.NewServer())

go srv.Serve(lis)

// On shutdown signal:
stopped := make(chan struct{})
go func() { srv.GracefulStop(); close(stopped) }()
select {
case <-stopped:
case <-time.After(15 * time.Second):
    srv.Stop()
}

Interceptor Pattern

func loggingInterceptor(ctx context.Context, req any, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (any, error) {
    start := time.Now()
    resp, err := handler(ctx, req)
    log.Printf("method=%s duration=%s code=%s", info.FullMethod, time.Since(start), status.Code(err))
    return resp, err
}

Client Implementation

• Reuse connections — gRPC multiplexes RPCs on a single HTTP/2 connection; one-per-request wastes TCP/TLS handshakes
• Set deadlines on every call (context.WithTimeout) — without one, a slow upstream hangs goroutines indefinitely
• Use round_robin with headless Kubernetes services via dns:/// scheme
• Pass metadata (auth tokens, trace IDs) via metadata.NewOutgoingContext

conn, err := grpc.NewClient("dns:///user-service:50051",
    grpc.WithTransportCredentials(creds),
    grpc.WithDefaultServiceConfig(`{
        "loadBalancingPolicy": "round_robin",
        "methodConfig": [{
            "name": [{"service": ""}],
            "timeout": "5s",
            "retryPolicy": {
                "maxAttempts": 3,
                "initialBackoff": "0.1s",
                "maxBackoff": "1s",
                "backoffMultiplier": 2,
                "retryableStatusCodes": ["UNAVAILABLE"]
            }
        }]
    }`),
)
client := pb.NewUserServiceClient(conn)

Error Handling

Always return gRPC errors using status.Error with a specific code — a raw error becomes codes.Unknown, telling the client nothing actionable. Clients use codes to decide retry vs fail-fast vs degrade.

Code	When to Use
InvalidArgument	Malformed input (missing field, bad format)
NotFound	Entity does not exist
AlreadyExists	Create failed, entity exists
PermissionDenied	Caller lacks permission
Unauthenticated	Missing or invalid token
FailedPrecondition	System not in required state
ResourceExhausted	Rate limit or quota exceeded
Unavailable	Transient issue, safe to retry
Internal	Unexpected bug
DeadlineExceeded	Timeout

// ✗ Bad — caller gets codes.Unknown, can't decide whether to retry
return nil, fmt.Errorf("user not found")

// ✓ Good — specific code lets clients act appropriately
if errors.Is(err, ErrNotFound) {
    return nil, status.Errorf(codes.NotFound, "user %q not found", req.UserId)
}
return nil, status.Errorf(codes.Internal, "lookup failed: %v", err)

For field-level validation errors, attach errdetails.BadRequest via status.WithDetails.

Streaming

Pattern	Use Case
Server streaming	Server sends a sequence (log tailing, result sets)
Client streaming	Client sends a sequence, server responds once (file upload, batch)
Bidirectional	Both send independently (chat, real-time sync)

Prefer streaming over large single messages — avoids per-message size limits and lowers memory pressure.

func (s *server) ListUsers(req *pb.ListUsersRequest, stream pb.UserService_ListUsersServer) error {
    for _, u := range users {
        if err := stream.Send(u); err != nil {
            return err
        }
    }
    return nil
}

Testing

Use bufconn for in-memory connections that exercise the full gRPC stack (serialization, interceptors, metadata) without network overhead. Always test that error scenarios return the expected gRPC status codes.

Testing patterns and examples

Security

• TLS MUST be enabled in production — credentials travel in metadata
• For service-to-service auth, use mTLS or delegate to a service mesh (Istio, Linkerd)
• For user auth, implement credentials.PerRPCCredentials and validate tokens in an auth interceptor
• Reflection SHOULD be disabled in production to prevent API discovery

Performance

Setting	Purpose	Typical Value
keepalive.ServerParameters.Time	Ping interval for idle connections	30s
keepalive.ServerParameters.Timeout	Ping ack timeout	10s
grpc.MaxRecvMsgSize	Override 4 MB default for large payloads	16 MB
Connection pooling	Multiple conns for high-load streaming	4 connections

Most services do not need connection pooling — profile before adding complexity.

Common Mistakes

Mistake	Fix
Returning raw error	Becomes codes.Unknown — client can't decide whether to retry. Use status.Errorf with a specific code
No deadline on client calls	Slow upstream hangs indefinitely. Always context.WithTimeout
New connection per request	Wastes TCP/TLS handshakes. Create once, reuse — HTTP/2 multiplexes RPCs
Reflection enabled in production	Lets attackers enumerate every method. Enable only in dev/staging
codes.Internal for all errors	Wrong codes break client retry logic. Unavailable triggers retry; InvalidArgument does not
Bare types as RPC arguments	Can't add fields to string. Wrapper messages allow backwards-compatible evolution
Missing health check service	Kubernetes can't determine readiness, kills pods during deployments
Ignoring context cancellation	Long operations continue after caller gave up. Check ctx.Err()

Cross-References

• → See jimmy-skills@backend-go-context skill for deadline and cancellation patterns
• → See jimmy-skills@backend-go-error-handling skill for gRPC error to Go error mapping
• → See jimmy-skills@backend-go-observability skill for gRPC interceptors (logging, tracing, metrics)
• → See jimmy-skills@backend-go-testing skill for gRPC testing with bufconn