dotnet-service-communication

Higher-level routing skill for choosing the right service communication protocol. Provides a decision matrix mapping requirements (latency, direction, client type, payload format, browser support) to the five primary .NET communication protocols: gRPC, SignalR, SSE, JSON-RPC 2.0, and REST. Routes to specialized skills for implementation depth.

Out of scope: HTTP client factory patterns and resilience pipelines -- see [skill:dotnet-http-client] and [skill:dotnet-resilience]. Native AOT architecture and trimming strategies -- see [skill:dotnet-native-aot] for AOT compilation, [skill:dotnet-aot-architecture] for AOT-first design patterns, and [skill:dotnet-trimming] for trim-safe development.

Cross-references: [skill:dotnet-grpc] for gRPC implementation, [skill:dotnet-realtime-communication] for SignalR/SSE/JSON-RPC details, [skill:dotnet-http-client] for REST/HTTP client patterns. See [skill:dotnet-integration-testing] for testing service communication patterns.

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Decision Matrix

Use this matrix to choose the right protocol based on your requirements:

Requirement	gRPC	SignalR	SSE	JSON-RPC 2.0	REST
Direction	All four patterns	Full-duplex	Server-to-client	Request-response	Request-response
Wire format	Protobuf (binary)	JSON or MessagePack	Text (JSON lines)	JSON	JSON/XML
Browser support	gRPC-Web (proxy needed)	Yes (JS client)	Yes (native EventSource)	Via WebSocket	Yes (fetch/XHR)
Contract	.proto schema	Hub interface	Convention	JSON-RPC spec	OpenAPI/Swagger
Latency	Lowest	Low	Low	Medium	Medium
Throughput	Highest	High	Moderate	Moderate	Moderate
Streaming	All 4 patterns	Server + client streaming	Server push only	No	No (chunked transfer)
Connection	HTTP/2 persistent	WebSocket (with fallback)	HTTP/1.1+ persistent	Transport-dependent	Per-request
Service-to-service	Excellent	Good	Limited	Niche	Good
AOT-friendly	Yes (Protobuf)	Yes	Yes	Yes	Yes (with STJ source gen)

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Decision Flowchart

Is this service-to-service (no browser)?
├── Yes → Do you need streaming?
│   ├── Yes → gRPC streaming [skill:dotnet-grpc]
│   └── No → Is it request-response?
│       ├── High throughput / binary → gRPC (unary) [skill:dotnet-grpc]
│       └── Standard CRUD / public API → REST [skill:dotnet-http-client]
└── No (browser client) → Do you need real-time?
    ├── Yes → Do you need bidirectional?
    │   ├── Yes → SignalR [skill:dotnet-realtime-communication]
    │   └── No (server push only) → SSE [skill:dotnet-realtime-communication]
    └── No → REST [skill:dotnet-http-client]

Special cases:
- LSP / tooling protocol → JSON-RPC 2.0 [skill:dotnet-realtime-communication]
- Mixed (browser + service-to-service) → REST for browser, gRPC for internal

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Protocol Profiles

gRPC

Best for: Service-to-service communication, high-throughput streaming, strongly-typed contracts.

• Schema-first development with .proto files
• All four streaming patterns: unary, server streaming, client streaming, bidirectional
• Binary serialization (Protobuf) for smallest payloads and fastest throughput
• Built-in code generation for client and server stubs
• Native load balancing and health check protocol support

When NOT to use: Direct browser communication (requires gRPC-Web proxy), simple CRUD APIs consumed by external clients, scenarios where human-readable payloads are required.

See [skill:dotnet-grpc] for full implementation details.

SignalR

Best for: Browser-facing real-time applications, interactive dashboards, chat, collaborative features.

• Automatic transport negotiation (WebSocket → SSE → Long Polling)
• Built-in group management and user targeting
• Hub abstraction with strongly-typed interfaces
• Scales with Redis backplane or Azure SignalR Service
• Supports JSON and MessagePack serialization

When NOT to use: Server-to-client-only push (use SSE instead), service-to-service (use gRPC instead), scenarios where the SignalR client library cannot be included.

See [skill:dotnet-realtime-communication] for SignalR patterns and hub implementation.

Server-Sent Events (SSE)

Best for: Simple server-to-client push notifications, live feeds, status updates.

• Built-in to ASP.NET Core in .NET 10 via TypedResults.ServerSentEvents
• Browser-native EventSource API -- no client library needed
• Automatic reconnection with Last-Event-ID
• Works through HTTP/1.1 proxies that block WebSocket upgrade
• Lightest-weight real-time option

When NOT to use: Bidirectional communication (use SignalR), high-throughput binary streaming (use gRPC), client-to-server messages needed.

See [skill:dotnet-realtime-communication] for SSE implementation details.

JSON-RPC 2.0

Best for: Tooling protocols (Language Server Protocol), structured RPC over simple transports.

• Transport-agnostic (HTTP, WebSocket, stdio, named pipes)
• Well-defined request/response/notification semantics
• Used by Visual Studio, VS Code, and .NET tooling via StreamJsonRpc
• Lightweight alternative to gRPC when schema management is unwanted

When NOT to use: Real-time streaming (use SignalR or gRPC), high-throughput service-to-service (use gRPC), standard web APIs (use REST).

See [skill:dotnet-realtime-communication] for JSON-RPC 2.0 patterns.

REST (HTTP APIs)

Best for: Public APIs, standard CRUD operations, broad client compatibility.

• Universal client support (any HTTP client)
• Human-readable payloads (JSON)
• Rich ecosystem (OpenAPI, Swagger UI, API versioning)
• Stateless request-response model
• ASP.NET Core Minimal APIs or MVC controllers

When NOT to use: Real-time push (use SSE or SignalR), high-throughput service-to-service (use gRPC), bidirectional streaming (use SignalR or gRPC).

See [skill:dotnet-http-client] for HTTP client patterns, resilience, and IHttpClientFactory.

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Common Architecture Patterns

API Gateway with Mixed Protocols

Browser ─── REST/SignalR ──→ API Gateway ──→ gRPC ──→ Internal Services
                                          ──→ gRPC ──→ Order Service
                                          ──→ gRPC ──→ Inventory Service

Use REST for public-facing APIs and SignalR for real-time browser features. Internal service-to-service communication uses gRPC for performance. The API gateway translates between protocols.

Event-Driven with SSE

Internal Services ──→ Message Broker ──→ SSE Endpoint ──→ Browser Dashboard
                                     ──→ gRPC Stream  ──→ Monitoring Service

Internal events flow through a message broker. Browser dashboards consume via SSE. Other services consume via gRPC streaming for higher throughput.

Dual-Protocol Services

A single ASP.NET Core host can serve both gRPC and REST:

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddGrpc();
builder.Services.AddControllers();

var app = builder.Build();

// gRPC for internal service-to-service
app.MapGrpcService<OrderGrpcService>();

// REST for external clients
app.MapControllers();

// SSE for real-time browser updates
app.MapGet("/events/orders", (OrderEventService svc, CancellationToken ct) =>
    TypedResults.ServerSentEvents(svc.GetEventsAsync(ct)));

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Key Principles

• Use gRPC for service-to-service -- it provides the best throughput, strongly-typed contracts, and all streaming patterns
• Use REST for public APIs -- universal client support, human-readable, extensive tooling ecosystem
• Use SignalR for browser real-time -- automatic transport negotiation and built-in group management
• Use SSE for simple server push -- lightest option when bidirectional communication is not needed
• Mix protocols when appropriate -- a single ASP.NET Core host can serve gRPC, REST, SignalR, and SSE simultaneously
• Route based on client type -- browser clients get REST/SignalR/SSE; internal services get gRPC

See [skill:dotnet-native-aot] for AOT compilation pipeline and [skill:dotnet-aot-architecture] for AOT-compatible communication patterns.

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Agent Gotchas

1. Do not default to gRPC for browser-facing APIs -- browsers cannot speak HTTP/2 trailers natively. Use gRPC-Web with a proxy or choose REST/SignalR/SSE.
2. Do not use SignalR for service-to-service -- gRPC provides better performance, code generation, and streaming for backend communication.
3. Do not add SignalR when SSE suffices -- if you only need server-to-client push, SSE is simpler, requires no client library, and has automatic reconnection built into browsers.
4. Do not use REST for high-throughput internal communication -- JSON text serialization and per-request connections add overhead vs gRPC's binary format and persistent HTTP/2 connections.
5. Do not forget AOT considerations -- REST endpoints using System.Text.Json need source-generated contexts for AOT. See [skill:dotnet-serialization] for details.
6. Do not expose gRPC services to untrusted clients without gRPC-Web -- raw gRPC requires HTTP/2, which is not universally available in all environments (e.g., some proxies, older browsers).

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References

• Choose between gRPC and REST
• gRPC for .NET
• SignalR overview
• Server-Sent Events in .NET 10
• Minimal APIs
• IHttpClientFactory patterns