Avoiding Cachepocalypse in the Land of the Monolith

Wednesday, March 22, 2023 - 4:00 pm4:20 pm

David Amin, Duolingo


Like many companies who switched to a microservice architecture, Duolingo runs a legacy monolith that is both business critical and not entirely owned by any one team. This monolith hit a scaling limit by exhausting memcached connections, but strangely only on a single node of the cluster. What followed was a debugging journey that spanned Python and C, took down production for an hour, and required binary arithmetic to solve. The talk will suggest strategies for mitigating unclear ownership of legacy systems, creating a fast and safe feedback loop for debugging in difficult circumstances, and coordinating a multi-team response to issues that threaten business continuity.

David Amin, Duolingo

David is an SRE on the Observability team at Duolingo, working on measuring what matters to millions of learners. He is based in New York and has previously worked in web hosting, fintech, and defense.

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@conference {286220,
author = {David Amin},
title = {Avoiding Cachepocalypse in the Land of the Monolith},
year = {2023},
address = {Santa Clara, CA},
publisher = {USENIX Association},
month = mar

Presentation Video