---
name: nestjs-real-time-94325150bae9
description: Implement WebSocket gateways with Socket.io and Server-Sent Events endpoints in NestJS. Use when building chat features, live feeds, or choosing between WebSocket and SSE for real-time communication.
metadata:
  triggers:
    files:
    - '**/*.gateway.ts'
    - '**/*.controller.ts'
    - 'Socket.io'
    keywords:
    - WebSocketGateway
    - SubscribeMessage
    - Sse
---
# Real-Time & WebSockets

## **Priority: P1 (HIGH)**


## Workflow: Add Real-Time Feature

1. **Choose protocol** — WebSocket for bi-directional (chat, collab); SSE for uni-directional (feeds, notifications).
2. **Implement gateway or SSE** — Create `@WebSocketGateway()` or `@Sse()` controller.
3. **Add auth** — Validate JWT in `handleConnection()` for WebSocket; use standard guards for SSE.
4. **Scale** — Add `@socket.io/redis-adapter` for multi-pod WebSocket; use HTTP/2 for SSE.
5. **Test connections** — Verify WebSocket handshake auth rejects invalid tokens; confirm SSE streams data.

## SSE Endpoint Example

See [implementation examples](references/example.md)

## WebSocket Gateway with Auth Example

See [implementation examples](references/example.md)

## Protocol Selection

- **WebSockets (Bi-directional)**: Use for Chat, Multiplayer Games, Collaborative Editing.
 - _High Complexity_: Requires custom scaling (Redis Adapter) and sticky sessions (sometimes).
- **Server-Sent Events (SSE) (Uni-directional)**: Use for Notifications, Live Feeds, Tickers, CI Log streaming.
 - _Low Complexity_: Standard HTTP. Works with standard Load Balancers. Easy to secure.
 - _NestJS_: Use `@Sse('route')` returning `Observable<MessageEvent>`.
- **Long Polling**: Use **only** as fallback or for extremely low-frequency updates (e.g., job status check every 10m).
 - _Impact_: High header overhead. Blocks threads if not handled carefully.

## WebSockets Implementation

- **Socket.io**: Default choice. Features "Rooms", "Namespaces", and automatic reconnection. Heavy protocol.
- **Fastify/WS**: Use `ws` adapter if performance critical (e.g., high-frequency trading updates) and you don't need "Rooms" logic.

## Scaling (Critical)

- **WebSockets**: In K8s, client connects to Pod . If Pod B emits event, client won't receive it.
 - **Solution**: **Redis Adapter** (`@socket.io/redis-adapter`). Every pod publishes to Redis; Redis distributes to all other pods.
- **SSE**: Stateless. No special adapter needed, but aware of **Connection Limits** (6 concurrent connections per domain in HTTP/1.1; virtually unlimited in HTTP/2).
 - **Rule**: Must use **HTTP/2** for SSE at scale.

## Security

- **Handshake Auth**: Standard HTTP Guards don't trigger on Ws connection efficiently.
 - **Pattern**: Validate JWT during `handleConnection()` lifecycle method. Disconnect immediately if invalid.
- **Rate Limiting**: Sockets expensive. Apply strict throttling on "Message" events to prevent flooding.

## Architecture

- **Gateway != Service**: `WebSocketGateway` should **only** handle client comms (Join Room, Ack message).
 - **Rule**: Delegate business logic to Service or Command Bus.
- **Events**: Use `AsyncApi` or `SocketApi` decorators (from community packages) to document WS events similarly to OpenAPI.


## Anti-Patterns

- **No HTTP guards for WebSocket auth**: Validate JWT in `handleConnection()`; HTTP guards don't trigger on WS.
- **No WebSocket at scale without Redis adapter**: Without `@socket.io/redis-adapter`, cross-pod events lost.
- **No SSE over HTTP/1.1 at scale**: Use HTTP/2 to avoid 6-connection-per-domain browser limit.

---
Source attribution: HoangNguyen0403
Original project: https://github.com/HoangNguyen0403/agent-skills-standard
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2026 Gabriel Moreira

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: HoangNguyen0403
Original project: https://github.com/HoangNguyen0403/agent-skills-standard
Attribution basis: Upstream repository explicitly recorded in package mirror path

Fields of work: Development & Engineering, Product Management
Roles: Backend Developer, Full-Stack Developer, Product Manager
Specialties: Backend
Tools: Nestjs, Socket.Io
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: 7b163e34637c4b7bbafef71113ee231867708c539764e3b8b737b80994343702