Building Scalable Real-Time Systems with WebSockets

Introduction

Handling millions of concurrent WebSocket connections efficiently is not just a technical challenge—it's an architectural one. In this post, we'll explore how we built a scalable real-time system that powers live updates, chats, and dashboards across our platform.

When we started, traditional HTTP polling was becoming unsustainable as our user base grew. We needed an event-driven solution with low latency and high concurrency. Here's what we built.

The Challenge

Traditional HTTP polling quickly became unsustainable as our user base grew. We needed an event-driven solution with low latency and high concurrency.

Key Requirements

• Support for 10M+ concurrent connections
• Sub-100ms message delivery latency
• Horizontal scalability across multiple regions
• Graceful failover and recovery
• Efficient resource utilization

Our Architecture

We designed a multi-layered architecture that separates concerns and scales independently:

1. Load Balancing Layer

NGINX with sticky sessions ensures that clients maintain their connection to the same server during their session. This is critical for WebSocket connections which are stateful by nature.

upstream websocket_backend {
    ip_hash;
    server ws1.example.com:3000;
    server ws2.example.com:3000;
    server ws3.example.com:3000;
}

server {
    location /ws {
        proxy_pass http://websocket_backend;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
    }
}