Real-time features are increasingly expected in modern web applications. Let's explore two key technologies for implementing them: WebSockets and Server-Sent Events (SSE). For request/response endpoints, see API design best practices for REST and GraphQL.
The key takeaway
Use WebSockets when client and server both need to send real-time messages, as in chat, collaborative editing, multiplayer games and trading platforms. Use Server-Sent Events for one-way server pushes such as notifications, live feeds, dashboards and progress updates, because SSE is simpler, runs over standard HTTP and reconnects automatically.
Understanding WebSockets
WebSockets provide full-duplex communication channels over a single TCP connection. Both client and server can send messages independently.
WebSocket Use Cases:
- Chat Applications: Real-time messaging requires bidirectional communication
- Collaborative Tools: Google Docs-style real-time editing
- Gaming: Multiplayer games with frequent client-to-server updates
- Trading Platforms: Real-time price updates with user actions
WebSocket Advantages:
- Full-duplex bidirectional communication
- Lower latency for frequent updates
- Efficient for high-frequency messaging
- Wide browser support
WebSocket Challenges:
- More complex to implement and maintain
- Requires special infrastructure (load balancers, scaling)
- Connection management complexity
- Not HTTP-friendly (proxies, firewalls)
Understanding Server-Sent Events (SSE)
SSE enables servers to push data to clients over standard HTTP. It's simpler than WebSockets but only supports server-to-client communication.
SSE Use Cases:
- News Feeds: Real-time updates pushed from server
- Notifications: Push notifications to web clients
- Live Dashboards: Analytics and monitoring displays
- Progress Updates: Long-running operation status
SSE Advantages:
- Simple to implement (built on HTTP)
- Automatic reconnection built-in
- Works with existing HTTP infrastructure
- Event IDs to support resumption when the server implements replay
- Text-based protocol (easy debugging)
SSE Limitations:
- Unidirectional (server to client only)
- Browser connection limits depend on HTTP version and deployment; review the actual transport and proxy configuration
- Text data only (no binary)
- Mobile support depends on the client implementation and platform
Performance Comparison
| Feature | WebSockets | SSE |
|---|---|---|
| Direction | Bidirectional | Server to Client |
| Protocol | Custom over TCP | HTTP/2 or HTTP/1.1 |
| Data Format | Binary or Text | Text only |
| Browser Support | Excellent | Good (not IE) |
| Reconnection | Manual | Automatic |
When should you use WebSockets or SSE?
When to Use WebSockets:
Choose WebSockets when you need client-to-server real-time communication, such as chat apps, collaborative editing, or multiplayer games.
When to Use SSE:
Use SSE for one-way server-to-client updates like notifications, live feeds, or progress indicators. It's simpler and often sufficient.
Scaling Considerations
Both technologies require careful planning for scale. Consider using Redis for pub/sub messaging, sticky sessions for load balancing, and proper connection management.
What are the alternatives to WebSockets and SSE?
Consider WebRTC for peer-to-peer communication, or frameworks like Socket.io that provide fallbacks and additional features.
Actinode has implemented real-time features in applications ranging from chat systems to live dashboards. We'll help you choose and implement the right technology for your requirements — see real examples in our case studies.
Questions and answers
What is the key difference between WebSockets and Server-Sent Events?
WebSockets provide full-duplex bidirectional communication — both client and server can send messages independently. SSE is unidirectional — the server pushes data to the client over standard HTTP. If users never need to send real-time data to the server, SSE is often simpler and sufficient.
When should I use WebSockets?
Use WebSockets for chat applications requiring real-time messaging, collaborative editing tools (like Google Docs), multiplayer games with frequent client-server updates, and trading platforms where users trigger actions based on live data.
When is SSE a better choice than WebSockets?
SSE is better for one-way server pushes: news feeds, push notifications to web clients, live dashboards, and progress indicators for long-running operations. It's simpler to implement, uses standard HTTP, and has built-in automatic reconnection.
How do I scale WebSocket connections across multiple servers?
Use Redis pub/sub for message broadcasting across server instances, configure sticky sessions on your load balancer so clients reconnect to the same server, and manage connection state carefully to handle disconnects gracefully.