Vitor Pellegrino, Zhen Zhou discuss how they built/test an on-demand notification system, what it takes to manage resources/site-reliability at the same time, and how to mitigate reliability issues.

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Duolingo created a high-scale notification system to send millions of notifications within seconds during the Super Bowl. They discussed their transition from a monolithic application to a microservices architecture using AWS ECS, Terraform, Python, and JVM languages. Key tools include Zombie mode for continuous user experience during backend issues, Jeeves for monitoring user feedback, and Freeze Gun to maintain user streaks during incidents. The Superb Owl service demonstrated the ability to send notifications quickly and reliably by leveraging asynchronous processing and AWS services.

How We Created a High-Scale Notification System at Duolingo