Slack's Migration to a Cellular Architecture

Cellular service architectures are a conceptually simple way for highly available online services to limit the impact of cascading failures and improve scale-out. So why aren't we all using them? And how do they even work in practice? 

In this talk, we'll explore Slack's transformative 18-month journey from a traditional multi-AZ architecture to a robust cellular architecture. Triggered by a critical incident in June 2021, this architectural shift revolutionized Slack's approach to system resilience and failure mitigation. We'll delve into the motivation behind the work, the operational characteristics of our particular implementation, challenges and complexities posed by the migration, and limitations of our approach as compared to others.

Attendees will gain insights into designing for failure in large-scale distributed systems, techniques for graceful degradation and traffic management, balancing consistency requirements with availability in cellular architectures, and strategies for executing major architectural changes while maintaining service quality.