Cases2 cases

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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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2. IL-0368 PlanetScale's control plane went down and some database branches failed queries during the AWS us-east-1 outage

   PlanetScale2025

   Symptoms

   At 7:13 UTC on 20 October 2025, PlanetScale's continuous tests in production started failing because they could not create new database branches. The service that creates, resizes and configures database branches was unavailable, a near-total control plane outage, while existing database branches kept their capacity and connectivity.

   Service outageScale-up failureNetwork unreachableHigh error rateReplication lagDNS resolution failures

   Trigger

   The incident started with a DNS misconfiguration at one of PlanetScale's service providers. An Amazon DynamoDB outage impacted AWS STS, and several hours of capacity constraints and network instability in AWS us-east-1 followed.

   Root cause

   Cloud provider outage

   Component

   DatabaseDatabase replicationDatabase proxy and connection poolerObject storage

   Contributing factor

   –

   Detection

   PlanetScale's continuous testing in production started failing and alerted engineers at 7:13 UTC. At 10:05 UTC an alert fired for a Kubernetes operator in a large single-tenant customer installation exhausting its resources.

   Remediation

   • Disallowed new databases in us-east-1 and made us-east-2 the default region for new databases
   • Delayed new backups and cancelled pending backups that were waiting for an EC2 instance
   • Advised PlanetScale Managed customers with vtgate autoscaling to shed load
   • Paused draining and terminating EC2 instances older than 30 days
   • Kept vacant EC2 instances for reuse instead of terminating them
   • Bin-packed vtgate processes more tightly for customers with autoscaling
   • Sent manual reparent requests to move primaries to healthier availability zones
   • Restarted the edge load balancer and vtgate processes that did not recover after the partitions healed

   Action items

   • Understand and become resilient to the failure modes of SaaS dependencies for CI/CD, SSO, web application hosting and incident communication
   • Investigate more ambitious ways to reduce runtime dependence on internal and AWS services
   • Look into using all six us-east-1 availability zones to tolerate zonal outages and partitions

   Lessons

   Keeping the control plane separate from the data plane meant the control plane outage did not affect customer databases, and redundancy, automated failover and zonal traffic routing limited the effect of the network partitions. Network partitions are hard to reason about, test and tolerate: with three availability zones a system survives losing one zone only if the other two can still reach each other reliably.

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