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1. IL-0357 Up to 22% of Vercel static file requests failed when part of its global cache was lost during the AWS us-east-1 outage

   Vercel2025

   Symptoms

   On 20 October 2025 at 07:45 UTC, while Vercel was moving traffic away from its us-east-1 region (iad1) during the AWS us-east-1 outage, a cascading failure took out a percentage of Vercel's global caching infrastructure. Failures of static file serving peaked at about 22% of traffic, the largest impact of the whole event, until service was restored at 08:18 UTC.

   High error rate

   Trigger

   The AWS us-east-1 region (Vercel's iad1) failed on 20 October 2025, and Vercel began re-routing traffic and function invocations away from it; at 07:45 UTC a cascading failure followed in the global caching infrastructure.

   Root cause

   Cloud provider outage

   Component

   CDN and edge networkObject storage

   Contributing factor

   –

   Detection

   The first automated alerts, for errors across Vercel services, fired at 06:55 UTC at the start of the us-east-1 disruption, 50 minutes before the cache failure began; incidents were created automatically and on-call engineers were paged.

   Remediation

   • Re-routed end-user traffic away from iad1 into neighbouring data centers
   • Re-routed function invocations to configured backup or secondary regions
   • Restored static file serving at 08:18 UTC and mitigated the root cause of the cascading cache failure

   Action items

   • Write a detailed technical postmortem leading to systematic mitigation of the failure modes these disruptions exposed
   • Continue and intensify rehearsals of major regional disruptions

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