All 15 gRPC Services questions
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What is protobuf field numbering, and why must you never reuse or renumber a field once a message definition has shipped to production? How would you version a gRPC service's contract while maintaining backward compatibility with existing clients? How does client-side load balancing work for gRPC when calling a service with multiple backend instances, without a dedicated load balancer? What are the four types of gRPC service methods (unary, server streaming, client streaming, bidirectional streaming), and when is each appropriate? How does gRPC's use of HTTP/2 multiplexing provide performance advantages over HTTP/1.1-based REST APIs? How does gRPC support interceptors for cross-cutting concerns like authentication, logging, and retries, similar to middleware in a REST pipeline? How do you handle authentication for gRPC calls, and how does it differ from typical REST API authentication patterns? How do you configure deadlines and cancellation for gRPC calls, and how does this differ from typical HTTP request timeouts?
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How does gRPC handle errors and status codes, and how does this differ from HTTP status codes in REST?

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Answer

gRPC uses its own set of standardized status codes (like NotFound, InvalidArgument, PermissionDenied, Internal, Unavailable) distinct from HTTP status codes, communicated via gRPC trailers rather than the HTTP status line -- a server method throws an RpcException with a specific StatusCode and optional detail message, which the client-side generated code surfaces as a corresponding exception, giving a richer, RPC-appropriate error vocabulary than REST's more general-purpose HTTP status codes.
public override Task<OrderResponse> GetOrder(GetOrderRequest request, ServerCallContext context) {
    var order = _repository.Find(request.OrderId);
    if (order == null) {
        throw new RpcException(new Status(StatusCode.NotFound, $"Order {request.OrderId} not found"));
    }
    return Task.FromResult(MapToResponse(order));
}

// Client-side:
try {
    var response = await client.GetOrderAsync(request);
} catch (RpcException ex) when (ex.StatusCode == StatusCode.NotFound) {
    // handle specifically
}
Real-world example A gRPC client library automatically translates a server-thrown RpcException with StatusCode.PermissionDenied into a client-side exception the calling application can catch and handle specifically, distinct from how it would handle a StatusCode.Unavailable indicating a transient network issue.

Common follow-ups: How do you attach custom error details (like field-level validation errors) to an RpcException?;How does gRPC status code mapping relate to HTTP status codes when gRPC runs over HTTP/2?

Exception Handling;Global Exception Handling & Middleware
All 15 gRPC Services questions