Slack Engineering

Overview

Slack runs real-time messaging for hundreds of thousands of customer workspaces, including most of the Fortune 500, where a few seconds of message latency is a visible incident. The blog is strongest on three fronts: a cellular architecture migration that isolates blast radius by routing each workspace to a single cell, persistent WebSocket fleets at the millions-of-connections scale (including the Envoy migration), and enterprise-grade search that has to respect tenant isolation and per-channel ACLs. For interviews, 'Real-time Messaging at Slack' and 'Migrating Millions of Concurrent Websockets to Envoy' together form the reference architecture for any 'design a chat system' question, and 'Slack's Migration to a Cellular Architecture' anchors discussions of multi-tenant isolation.

Interview questions

• What topics does Slack engineering blog cover?
• What makes Slack's architecture posts valuable?
• Which Slack posts should I read before a chat-system design interview?

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