Why Real-Time APIs Matter
Modern applications rely on instant feedback. Whether it’s a chat message, stock ticker, or live dashboard, users expect updates without refreshing the page.
Traditional REST APIs fall short here — they require repeated polling, wasting bandwidth and increasing latency.
That’s why technologies like WebSockets and Server-Sent Events (SSE) are essential for real-time experiences.
The Challenge with REST
REST APIs work perfectly for request-response actions, but not for ongoing data streams.
If a server needs to push updates to many clients, polling or long-polling quickly becomes inefficient.
To solve this, we need persistent connections that let servers send data proactively.
What Are WebSockets?
WebSockets enable full-duplex communication — both the client and server can send messages anytime over a single TCP connection.
Once established, the connection stays open until either side closes it.
This makes WebSockets ideal for:
- Chat apps
- Multiplayer games
- Collaborative tools (like whiteboards or docs)
- Real-time dashboards
Example (Node.js):
const WebSocket = require('ws');
const server = new WebSocket.Server({ port: 8080 });
server.on('connection', socket => {
socket.send('Welcome!');
socket.on('message', msg => console.log('Received:', msg));
});
With WebSockets, latency is extremely low because there’s no need for repeated HTTP handshakes.
What Are Server-Sent Events (SSE)?
Server-Sent Events allow one-way communication — from server to client — over HTTP.
Unlike WebSockets, SSE doesn’t support client-to-server messaging (beyond normal HTTP requests).
They’re perfect for:
- Notifications
- Stock or sports tickers
- Live feeds and logs
Example (Express.js):
app.get('/events', (req, res) => {
res.setHeader('Content-Type', 'text/event-stream');
setInterval(() => res.write(`data: ${new Date()}\n\n`), 1000);
});
The browser automatically reconnects if the connection drops, making SSE reliable and simple to use.
Comparing WebSockets and SSE
| Feature | WebSockets | Server-Sent Events (SSE) |
|---|---|---|
| Direction | Two-way | One-way (server → client) |
| Protocol | TCP | HTTP |
| Complexity | Higher | Lower |
| Reconnection | Manual | Automatic |
| Use cases | Chat, games, collaboration | Feeds, notifications, analytics |
In short, WebSockets are better for interactive, bidirectional systems, while SSE is ideal for lightweight live updates.
When to Use Each
Choose WebSockets if:
- You need two-way interaction.
- You expect rapid, frequent updates.
- You can handle custom scaling (like using message brokers).
Choose SSE if:
- Updates only flow from server to client.
- You prefer simpler HTTP-based solutions.
- You want automatic reconnection and easier debugging.
Some teams even combine both — using WebSockets for chat and SSE for analytics dashboards.
Scaling Real-Time APIs
When scaling, the main challenge is state management.
Because WebSockets keep open connections, you must synchronize messages across multiple nodes.
Common solutions include:
- Redis Pub/Sub for broadcasting messages.
- Kafka for high-throughput event streaming.
- NATS or RabbitMQ for distributed systems.
If you use SSE, horizontal scaling is easier — connections are stateless and can be balanced through a reverse proxy like NGINX.
Best Practices
- Use access tokens to secure connections.
- Limit message size to prevent abuse.
- Implement ping/pong heartbeats to detect dropped clients.
- Add back-pressure handling for heavy streams.
- Monitor connection counts and memory usage carefully.
A small misconfiguration can cause hundreds of idle connections to overload your server.
Final Thoughts
Real-time APIs make applications more engaging and responsive.
Choosing between WebSockets and Server-Sent Events depends on your direction of communication, scalability goals, and complexity tolerance.
If you’re building distributed or event-driven backends, check out Designing Event-Driven Microservices with Kafka to see how real-time streams integrate into broader architectures.
For deeper insights into streaming APIs, visit MDN’s guide to WebSockets.
