January 2022 Summaries

This post by an Ably engineer discusses the use of Redis for key-based storage in their pub/sub messaging platform and how they resolved a problem related to maintaining the integrity of related keys when using expire operations within Lua scripts. The issue was that naively expiring multiple keys in the same script did not guarantee atomicity, leading to potential inconsistencies. The solution involved using EXPIREAT to set an absolute expiry time for all related keys and reordering key expiry to ensure consistency.

Realtime updates have become a standard feature in many applications and websites, providing users with up-to-the-minute information without the need for refreshing pages. The evolution of web technology has enabled asynchronous communication, allowing servers to send updates to clients as changes happen. WebSockets emerged as a solution for realtime, bidirectional communication on the web, offering an event-driven architecture that reduces processor usage and improves user experience. Realtime updates have numerous applications, including live sports scores, transportation tracking, online collaboration tools, and audience engagement features in livestreams. Companies like Ably provide cloud-based pub/sub messaging platforms to help organizations build scalable, reliable realtime communication systems.

Agile Flush is a realtime collaboration app built using Vue.js, Node.js, Ably, and Azure Static Web Apps. It's designed for scrum teams to use planning poker, a technique for estimating the size of user stories during sprint planning. The app allows team members to join their regular online planning call in their communication tool of choice and start voting immediately without needing to sign up or provide any information about themselves or the planning session. Agile Flush is open source and can be found on GitHub, with a detailed walkthrough provided for building and deploying the application.

The WebSocket technology has been standardized for over a decade and is now one of the main technologies powering the modern web, enabling event-driven, full-duplex communication between client and server with minimum overhead and low latency. WebSockets are ideal for building interactive, realtime digital experiences that provide delightful user experiences. The WebSocket Handbook is a resource for developers who want to learn about this technology and how to use it to build event-driven, realtime apps. It covers the core building blocks of the WebSocket technology, its characteristics, and advantages, as well as providing step-by-step walkthroughs on how to build realtime web apps with WebSockets and Node.js.

Ably is a platform for pub/sub messaging that operates across multiple regions. The original design involved a GlobalChannelResource responsible for determining active regions and communicating updates, but it had issues with activation speed, resource usage, and reliability in the face of regional disruptions. To address these problems, Ably implemented a new region discovery mechanism called 'channel global decoupling.' This change involves peer-to-peer region discovery without relying on a global role. The new design has significantly improved channel activation times, reduced resource usage, and increased reliability during regional disruptions.