gRPC with ASP.NET Core

Introduction

Internal ShopNest services (Inventory ↔ Warehouse) use gRPC for fast binary RPC with strongly typed .proto contracts — REST stays for public APIs; gRPC wins service-to-service.

After this article you will

• Define services in .proto files
• Implement gRPC server in ASP.NET Core
• Call from .NET client with generated stubs
• Use unary and streaming patterns
• Choose gRPC vs REST appropriately

Prerequisites

• Article 52 — Message Queues with RabbitMQ
• ShopNest API, EF Core, and DI from prior modules

Concept deep-dive

syntax = "proto3";
option csharp_namespace = "ShopNest.Inventory.Grpc";
service InventoryService {
  rpc GetStock (GetStockRequest) returns (StockReply);
  rpc WatchStock (WatchStockRequest) returns (stream StockReply);
}
message GetStockRequest { int32 product_id = 1; }
message StockReply { int32 product_id = 1; int32 quantity = 2; }

// Server Program.cs
builder.Services.AddGrpc();
app.MapGrpcService<InventoryGrpcService>();

// Client
var channel = GrpcChannel.ForAddress("https://inventory:5001");
var client = new InventoryService.InventoryServiceClient(channel);
var reply = await client.GetStockAsync(new GetStockRequest { ProductId = 42 });

gRPC-Web allows browser clients via proxy. Auth: JWT in metadata headers.

Hands-on — ShopNest High-Performance Internal Service Communication

1. Add Grpc.AspNetCore; create inventory.proto.
2. InventoryGrpcService implements GetStock from EF.
3. Order service client calls gRPC instead of REST for stock check.
4. Compare latency REST vs gRPC in local benchmark.

Common errors & best practices

• gRPC for public browser API without gRPC-Web — stick to REST/OpenAPI.
• Proto breaking changes without versioning — coordinate deployments.

Interview questions

Q: gRPC vs REST?
A: gRPC: HTTP/2, binary, contract-first, faster internal; REST: universal, human-readable, public APIs.

Q: Streaming types?
A: Server, client, bidirectional — for live stock feeds.

Summary

• Proto files define cross-service contracts
• gRPC ideal for internal ShopNest service mesh
• REST remains for external partners and mobile BFF
• GrpcChannel + generated client for callers

Previous: Message Queues with RabbitMQ
Next: Unit Testing with xUnit and Moq

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