🤯 Scaling Pains: Why Your SSE App Fails Under Load Balancers

The Hidden Cost of Real-Time: Managing Stateful Connections

Salih İbrahimbaş

4 min read

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Nov 26, 2025

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Developing real-time applications using Server-Sent Events (SSE) is an excellent way to deliver data efficiently. However, the moment you move your backend service beyond a single instance and deploy it behind a Load Balancer, you inevitably encounter the Statefulness Trap.

This article breaks down why any SSE application breaks when scaled horizontally across multiple server nodes and presents robust, language-agnostic architectural patterns to solve the problem without compromising performance.

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The Core Conflict: In-Memory State vs. Horizontal Scaling

Understanding SSE and Statefulness

SSE relies on a single, long-lived HTTP connection where the server pushes data to the client. When a user connects to a specific server node (say, Node A):

1. The operating system and the backend framework establish and maintain the continuous socket connection.
2. The server process (Node A) holds the unique reference (the stream handler or connection object) for this client in its local memory.
3. Your application maintains a…