Server-Sent Events (SSE) PoC .NET10 + Redis

This repository is a proof of concept (PoC) demonstrating how to implement Server-Sent Events (SSE) in .NET API for real-time streaming of newly created orders.

The PoC intentionally includes two implementations to highlight trade-offs:

1. In-memory streaming using Channel<T>
2. Redis-backed streaming using Redis Streams

Goals of this PoC

• Demonstrate modern SSE support in .NET API
• Show clean DI-based design
• Support multiple concurrent SSE clients
• Compare in-memory vs Redis-based approaches
• Highlight real-world edge cases (fan-out, race conditions, retention)

Implementation using In-Memory (Channel)

Description

• Uses System.Threading.Channels
• Single shared channel registered as a Singleton
• Natural fan-out to all connected SSE clients

When to use

• Local development
• Single-instance deployments
• Demos and experiments

Characteristics

• Fan-out: Yes
• Replay: No
• Multi-instance support: No
• Persistence: No
• Production-ready: No

Implementation using Redis Streams

Description

• Uses Redis Streams via StackExchange.Redis
• Each SSE connection maintains its own cursor
• Light polling is used (blocking reads are not supported)
• A replay-window pattern avoids race conditions

When to use

• Multiple instances / Kubernetes
• Real users
• Shared event source across pods

Characteristics

• Fan-out: Yes
• Replay: Bounded (via replay window)
• Multi-instance support: Yes
• Persistence: Yes (bounded)
• Production-ready: Yes

Replay Window Pattern

Redis Streams combined with polling can miss the first event when multiple clients connect simultaneously.

To avoid this, the PoC uses a replay window

High-Level Architecture

• create order
• publish OrderCreatedEvent
• SSE clients receive event via /api/order/stream

flowchart LR
    Client1[Browser / Client A]
    Client2[Browser / Client B]

    Client1 -->|SSE| StreamEndpoint
    Client2 -->|SSE| StreamEndpoint

    StreamEndpoint["GET /api/order/stream<br/>SSE Endpoint"]

    CreateOrder["POST /api/order<br/>Create Order API"]

    CreateOrder --> OrderService[Order Service]

    OrderService --> EventStream[IOrderEventStream]

    EventStream -->|In-Memory| InMemory[In-Memory Channel]
    EventStream -->|Redis| Redis[(Redis Streams)]

    InMemory --> StreamEndpoint
    Redis --> StreamEndpoint

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