Every time a product team decides to add real-time features, whether live notifications, activity feeds, dashboard updates, or collaborative editing, the conversation defaults to WebSockets. WebSockets are powerful, bidirectional, and well-supported. They are also significantly more complex to operate than most teams anticipate. Connection state management, reconnection logic, load balancer configuration, horizontal scaling with sticky sessions or pub/sub layers, and heartbeat mechanisms all add operational surface area that a simple HTTP-based architecture does not have. Server-Sent Events (SSE) solve the majority of real-time use cases with a fraction of the complexity, and understanding when each technology is the right choice saves teams from over-engineering their real-time infrastructure.
What SSE Actually Is and Why It Gets Overlooked
Server-Sent Events is a browser API built on standard HTTP. The client opens a long-lived HTTP connection to the server, and the server pushes text-based events down that connection as they occur. The browser handles reconnection automatically, including sending the last received event ID so the server can resume the stream without data loss. SSE works through every HTTP proxy, CDN, and load balancer without special configuration because it is just an HTTP response with a specific content type. There is no protocol upgrade, no frame parsing, and no binary message handling.
SSE gets overlooked because WebSockets arrived with more marketing momentum and because SSE only supports server-to-client communication. The bidirectional nature of WebSockets feels more capable, and developers default to the tool that can do more. But most real-time features in web applications are server-to-client: notifications pushed to the browser, dashboard metrics updating in real time, live feed items appearing as they are created, stock prices ticking, or deployment status changes streaming to a monitoring page. The client rarely needs to send data back through the same persistent connection. Standard HTTP POST requests handle client-to-server communication perfectly well.
The Infrastructure Cost of WebSockets
WebSockets require infrastructure accommodations that SSE does not. The WebSocket protocol starts as an HTTP request and upgrades to a persistent TCP connection with its own framing protocol. This upgrade breaks assumptions that HTTP-based infrastructure relies on. Load balancers need to be configured to handle the upgrade header and maintain long-lived connections rather than distributing requests round-robin. Many CDNs either do not support WebSocket connections or charge premium rates for them. HTTP/2 multiplexing, which allows multiple streams over a single TCP connection, does not apply to WebSocket connections, so each WebSocket client consumes a dedicated TCP connection on the server.
Horizontal scaling with WebSockets requires a pub/sub layer. When a user connects to Server A and another user connects to Server B, a message sent by the first user needs to reach the second user. Since the two connections terminate on different servers, a message broker like Redis Pub/Sub, NATS, or RabbitMQ must sit between them to distribute messages across server instances. This pub/sub layer adds latency, operational complexity, and another failure mode to the architecture. SSE connections that deliver server-generated events, such as database change notifications or background job completions, can use the same pub/sub layer but do not require it for the common case where each client receives its own personalized event stream.
Connection management is another area where WebSockets demand more engineering attention. WebSocket connections can silently die when the client's network changes, when a load balancer times out an idle connection, or when a proxy server closes what it perceives as an inactive TCP socket. Applications need heartbeat mechanisms to detect dead connections and reconnection logic to re-establish them. SSE handles reconnection natively. The browser's EventSource API automatically reconnects when a connection drops and sends the Last-Event-ID header so the server can replay missed events. This built-in resilience eliminates an entire category of bugs that WebSocket implementations must handle manually.
When WebSockets Are the Right Choice
WebSockets earn their complexity in applications that require high-frequency bidirectional communication. Collaborative editing, where every keystroke from every participant must be broadcast to all other participants in real time, is the canonical example. Multiplayer games, live trading platforms with order submission through the same channel, and interactive whiteboard applications all benefit from the persistent bidirectional channel that WebSockets provide. In these cases, the volume and frequency of client-to-server messages make standard HTTP requests impractical, and the WebSocket protocol's lower per-message overhead compared to HTTP headers matters at scale.
The decision criteria are straightforward. If the application needs to send more than a few messages per second from the client to the server through the persistent connection, use WebSockets. If the primary data flow is server-to-client with occasional client-to-server communication through standard form submissions or API calls, use SSE. If you are unsure, start with SSE. Migrating from SSE to WebSockets later is a manageable refactor if the requirements change, while starting with WebSockets when SSE would suffice means carrying unnecessary infrastructure complexity for the life of the feature.
Implementing SSE in Modern Frameworks
Modern web frameworks make SSE implementation straightforward. In Next.js, a route handler that returns a ReadableStream with the text/event-stream content type is all the server-side code required. The handler connects to the application's event source, whether that is a database change stream, a message queue, or a polling interval, and writes formatted SSE events to the stream. On the client, the native EventSource constructor opens the connection and provides onmessage and onerror callbacks. The entire implementation typically fits in under 50 lines of code on each side.
For applications that need SSE at scale, the architecture pattern is a thin SSE gateway that subscribes to an event bus and fans out events to connected clients. The gateway handles connection management and event formatting while the rest of the application publishes events to the bus without knowing or caring how they reach the client. This separation of concerns keeps the real-time delivery mechanism isolated from the business logic and makes it possible to swap SSE for WebSockets or any other delivery mechanism without changing the event producers.
Edge runtimes like Cloudflare Workers and Vercel Edge Functions support SSE natively, which enables real-time features without managing persistent server infrastructure. The edge runtime holds the client connection and streams events from an upstream source, leveraging the platform's global network to reduce latency between the server and the client. This deployment model is not possible with WebSockets on most edge platforms because the WebSocket protocol's stateful nature conflicts with the edge runtime's request-based execution model.
Practical Recommendations
For teams building real-time features today, the practical recommendation is to default to SSE for all server-to-client streaming and use standard HTTP endpoints for client-to-server communication. Reserve WebSockets for the specific cases where bidirectional streaming is genuinely required. This approach minimizes infrastructure complexity, leverages existing HTTP infrastructure without modification, and provides built-in reconnection resilience that WebSocket implementations must build manually.
MAPL TECH builds real-time web applications using the architecture that fits each use case, whether that is SSE for live dashboards and notification systems or WebSockets for collaborative features. Our approach prioritizes operational simplicity without sacrificing performance. Explore our web development services or schedule a consultation to discuss your real-time architecture needs.
