Senior/Staff System Design Interviews: WebSockets

Whether a senior/staff system design interview ends up meriting an offer often depends on how well one understands the architecture real-time/low-latency/globally-scaled web services. In today’s fast-paced digital era, the demand for real-time communication in web applications has surged exponentially. WebSockets have emerged in the past few decades to facilitate seamless and instantaneous data exchange between clients and servers. In this blog post, we’ll explore the mechanics behind WebSockets, their implementation specifics, and how they optimize server resources for ultra-responsive connections. So, let’s dive in!

How WebSockets Work

WebSockets operate on the principle of upgrading an existing HTTP connection to a persistent, full-duplex communication channel. When a client desires to establish a WebSocket connection, it sends a standard HTTP request to the server with an “Upgrade” header, expressing its intention. If the server supports WebSockets, it responds with a 101 status code, allowing the client to upgrade the connection. Once this handshake is complete, the WebSocket connection is established, enabling bi-directional data flow with minimized latency.

WebSockets employ the WebSocket protocol, a standardized technology evolving over time. The initial version, known as “RFC 6455,” was released in 2011, and it is the most widely adopted version in modern web browsers. This version of WebSocket used HTTP/1.1 for the handshake process. In recent years, there have been advancements in the protocol, such as WebSocket version “RFC 7692,” which offered data compression/more efficient transmission via the per-message deflate extension.

Example WebSocket URL

WebSocket URLs begin with either ws:// or wss://, depending on whether the connection is non-secure or secure, respectively. For instance, ws:// indicates a WebSocket connection for a chat application, while wss:// implies a secure WebSocket connection for handling secure notifications.

Optimizing for Performance

When it comes to server performance, optimizing WebSocket connections is crucial. Here are key considerations:

  • Resource Management: WebSocket connections are long-lived, and a large number of open connections could consume significant server resources. Employing efficient connection management strategies, such as connection pooling and limiting idle connections, can help optimize resource usage.
  • Bandwidth Reduction: WebSocket data frames have minimal headers, which reduces overhead compared to traditional HTTP requests. However, further bandwidth reduction can be achieved through data compression techniques like gzip or using WebSocket extensions like permessage-deflate.
  • CPU and Memory Usage: WebSocket connections can consume CPU and memory resources, especially when handling a high number of concurrent connections. Employing asynchronous programming paradigms, such as event loops or asynchronous I/O, can help mitigate CPU and memory bottlenecks.


WebSockets are highly versatile and find applications in various systems, including:

  • Real-Time Chat Applications: WebSockets enable instant messaging and real-time updates in chat platforms, enhancing user engagement.
  • Collaborative Tools: Systems facilitating real-time collaboration, like document editing or project management tools, rely on WebSockets to enable seamless team interactions.
  • Live Dashboards and Analytics: WebSockets empower live data streaming and real-time updates for dynamic dashboards and analytics applications.
  • Online Gaming: Real-time gaming applications rely on WebSockets to support smooth interactions and synchronize actions among players.
  • Financial Trading Platforms: WebSockets offer low-latency communication, making them invaluable for financial systems that require real-time updates on stock prices and trading data.

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