How Should I Structure a Web App That Needs Real-Time Updates

I’d go with SSE if you mainly need server-to-client updates. WebSockets make more sense when you need two-way communication. For production, handle reconnects with backoff, authenticate connections, and use Redis/pub-sub or a message broker when scaling across multiple servers.

WebSockets make sense when you need real-time two-way updates, while SSE works well for simpler server-to-client updates. I’d also focus on reconnect handling and scalability early—those can get tricky in production. This is something TechBuilder considers when building real-time apps.

It depends mostly on the direction of the data flow:

1. If updates only flow one way (server → client), like order status changes or new records appearing, Server-Sent Events (SSE) are usually enough and simpler than WebSockets. SSE runs over plain HTTP, auto-reconnects natively in the browser, and works through most proxies/load balancers without special config.

2. If you need two-way communication (chat, live cursors, collaborative editing, anything the client also needs to push), go with WebSockets. Don't reach for WebSockets just because it feels more "real-time" — it adds real complexity you don't need if the app is really just server-to-client notifications.

3. Skip polling once you're past a small user base. Even long-interval polling adds up fast and wastes server resources compared to either SSE or WebSockets holding a single open connection.

4. Reconnects: SSE handles this automatically (the browser reconnects and sends a Last-Event-ID header so you can resume from where it left off). For WebSockets, you have to build this yourself — exponential backoff on the client, and a way to resync state after a dropped connection (usually a "fetch latest state" REST call on reconnect, since you can't trust that you didn't miss messages while disconnected).

5. Authentication: for WebSockets, authenticate during the initial handshake (token in the connection URL or an initial auth message), not per-message. For SSE, the connection is just an HTTP request, so normal auth headers/cookies work fine.

6. Scalability: the real challenge isn't the protocol, it's fanning out messages across multiple server instances. You'll need a pub/sub layer (Redis Pub/Sub, or a managed service like Ably/Pusher) so that when instance A gets an update, it can notify clients connected to instances B and C. Sticky sessions or a shared connection registry are also needed since WebSocket/SSE connections are stateful per server.

In production, a common pattern is: SSE (or a managed real-time service) for simple one-way updates, WebSockets reserved for genuinely bidirectional features, and Redis pub/sub tying it together once you have more than one server instance.

WebSockets make sense when you need real-time two-way updates, while SSE works well for simpler server-to-client updates. I’d also focus on reconnect handling and scalability early—those can get tricky in production. This is something TechBuilder considers when building real-time apps.

It really depends on how much two-way communication your app needs. If the server mainly needs to push updates to users, SSE can be simpler and easier to manage. For applications where the client and server both need frequent real-time communication, WebSockets are usually a better fit.

For either approach, I’d design reconnect handling from the start, including retries with backoff and a way to resync missed updates after reconnecting. Authentication should also be handled during connection setup rather than relying only on the frontend.

For scalability, avoid keeping important state only in a single server instance. Using a shared message broker or pub/sub layer can help distribute events when the application runs across multiple servers.

A hybrid approach has worked best in my experience: SSE for one-way pushes like order status changes, and WebSockets only where the client also talks back, since each protocol has its own connection limits and failure modes. One thing worth adding early is a heartbeat message so the client can detect a dead connection and reconnect cleanly with backoff. Also, design for horizontal scale from the start: sticky sessions will bite you once traffic grows, so keep session state in a shared store rather than in memory.

I’d choose based on how the data flows. If the server just needs to push updates to the UI, SSE is often enough and simpler to maintain. If you need continuous two-way communication, WebSockets make more sense. Polling is still fine when updates don’t need to be instant.

For production, I’d pay just as much attention to reconnects, missed events, and authentication as the protocol itself. Use a way to recover missed updates after reconnecting, and consider Redis or a message broker when scaling across multiple server instances. The best architecture is the simplest one that meets the actual latency and reliability requirements.