WebSocket Communication
Explore how WebSocket protocol supports persistent, full-duplex communication for real-time use cases like collaborative editing and live dashboards. Understand connection lifecycle, server-client management, scaling challenges, and architectural trade-offs essential for designing responsive distributed systems.
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Consider a collaborative document editor in which five engineers edit the same file simultaneously. Every keystroke must propagate to all participants within milliseconds. Or picture a live trading dashboard where price ticks arrive dozens of times per second, and a 200ms polling delay means acting on stale data. In the previous lesson, we explored how the publish-subscribe pattern decouples services through broker-mediated event fan-out, enabling scalable asynchronous communication. But pub-sub operates between backend services. When the requirement shifts to a persistent, low-latency, bidirectional channel directly between a client and a server, a different mechanism is needed.
WebSocket is the protocol designed to solve exactly this problem. This lesson covers how WebSockets work, their connection life cycle, real-world use cases, and the architectural trade-offs they introduce in system design.
How the WebSocket protocol works
WebSocket is a full-duplex communication protocol that operates over a single, long-lived TCP connection. Unlike HTTP, where the client must initiate every exchange, WebSocket allows both sides to send messages independently at any time after the connection is established.
The HTTP upgrade handshake
Every WebSocket connection begins its life as a standard HTTP request. The client sends an HTTP GET request that includes an Upgrade: websocket header, signaling its intent to switch protocols. The server, if it supports WebSocket, responds with an HTTP status 101 Switching Protocols. At that moment, the underlying TCP connection transitions from the HTTP request-response model to the WebSocket frame-based protocol. No new TCP connection is created; the existing one is repurposed.
After the handshake completes, communication shifts to a lightweight ...