Server-Sent Events (SSE) provide a simple way to stream data from server to client. Here's how to implement them effectively.
Basic SSE Server
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SSE Message Format
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Client Implementation
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React Hook
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Authentication and Headers
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Pub/Sub Pattern
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Scaling with Redis
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Next.js Route Handler
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SSE vs WebSocket
SSE:
✓ Simple to implement
✓ Automatic reconnection
✓ HTTP/2 multiplexing
✓ Works through firewalls
✗ Server-to-client only
✗ Limited browser connections (6 per domain)
WebSocket:
✓ Bidirectional
✓ Binary data support
✓ Lower latency
✗ More complex
✗ Manual reconnection
✗ May need special proxy config
Choose SSE for:
- Notifications
- Live feeds
- Progress updates
- Server-initiated updates
Choose WebSocket for:
- Chat applications
- Real-time collaboration
- Gaming
- Client-initiated events
Best Practices
Connection:
✓ Set correct headers
✓ Flush headers immediately
✓ Clean up on disconnect
✓ Use heartbeats for keep-alive
Scaling:
✓ Use Redis for multi-server
✓ Limit connections per user
✓ Monitor connection count
✓ Handle reconnection gracefully
Performance:
✓ Send only necessary data
✓ Batch updates when possible
✓ Use event IDs for resume
✓ Set appropriate retry interval
Conclusion
Server-Sent Events provide a simple, reliable way to stream data from server to client. They're perfect for notifications, live feeds, and progress updates. Use Redis for scaling across multiple servers, implement proper authentication, and consider WebSockets only when you need bidirectional communication.