A deep dive into the technology behind building Slack. Written by engineers, for engineers passionate about solving complex technical problems.
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This story describes the technical details of the problems that caused the Slack downtime on May 12th, 2020. To learn more about the process behind incident response for same outage, read Ryan Katkov’s post, “All Hands on Deck”. On May 12, 2020, Slack had our first significant outage in a long time. We published a…
Summary In recent years, cellular architectures have become increasingly popular for large online services as a way to increase redundancy and limit the blast radius of site failures. In pursuit of these goals, we have migrated the most critical user-facing services at Slack from a monolithic to a cell-based…
And now we welcome the new year. Full of things that have never been. — Rainer Maria Rilke January 4th 2021 was the first working day of the year for many around the globe, and for most of us at Slack too (except of course for our on-callers and our customer experience team, who never…
By Laura Nolan, with contributions from Glen D. Sanford, Jamie Scheinblum, and Chris Sullivan. Assessing conditions Slack experienced a major incident on February 22 this year, during which time many users were unable to connect to Slack, including the author — which certainly made my role as Incident Commander more…
If you are are an engineer whose organization uses Linux in production, I have two quick questions for you: 1) How many unique outbound TCP connections have your servers made in the past hour? 2) Which processes and users initiated each of those connections? If you can answer both of these questions, fantastic! You…
Slack has a global customer base, with millions of simultaneously connected users at peak times. Most of the communication between users involves sending lots of tiny messages to each other. For much of Slack’s history, we’ve used HAProxy as a load balancer for all incoming traffic. Today, we’ll talk about problems we…
From the very beginning of Slack, MySQL was used as the storage engine for all our data. Slack operated MySQL servers in an active-active configuration. This is the story of how we changed our data storage architecture from the active-active clusters over to Vitess — a horizontal scaling system for MySQL. Vitess is…