Surviving Black Friday: 329B requests with Falcon

On Black Friday 2025, Shopify's Storefront served billions of requests on Falcon—85 million RPM at peak, zero dropped requests. One year earlier, we ran three different web servers and had no idea which parts of our 15-year-old Rails codebase were thread-safe. This talk brings together three perspectives on migrating a massive Ruby application to Falcon: Samuel Williams built Falcon and explains how it works — fibers, the async scheduler, and Long Tasks. He also investigates and fixes Crisis 3: the silent worker death caused by a torn pipe write in async-container. Marc-Andre Cournoyer sets the scene: Shopify's Storefront Renderer, why Unicorn was showing its limits, and the bet to ship Falcon before BFCM. He covers the October rollback and closes with results and lessons.

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