nestjs-real-time
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.
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SKILL.md
Real-Time & WebSockets
Priority: P1 (HIGH)
Workflow: Add Real-Time Feature
- Choose protocol — WebSocket for bi-directional (chat, collab); SSE for uni-directional (feeds, notifications).
- Implement gateway or SSE — Create
@WebSocketGateway()or@Sse()controller. - Add auth — Validate JWT in
handleConnection()for WebSocket; use standard guards for SSE. - Scale — Add
@socket.io/redis-adapterfor multi-pod WebSocket; use HTTP/2 for SSE. - Test connections — Verify WebSocket handshake auth rejects invalid tokens; confirm SSE streams data.
SSE Endpoint Example
WebSocket Gateway with Auth Example
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')returningObservable<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
wsadapter 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:
WebSocketGatewayshould only handle client comms (Join Room, Ack message). - Rule: Delegate business logic to Service or Command Bus.
- Events: Use
AsyncApiorSocketApidecorators (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.
Files
3- SKILL.md
94325150ba3.5 KB - evals/evals.json
321b61f7ef2.3 KB - references/example.md
9aa463e867970 B
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