Fly.io Upstash Redis service distruption (FRA region)

Summary

Fly.io Upstash Redis service distruption (FRA region)

On May 12th and 13th at various times, a subset of Upstash Redis instances on [Fly.io](http://Fly.io) experienced intermittent hangs and elevated error rates. The Redis process would stall inside a logging syscall — alive but not making progress — which made the issue hard to spot from our usual telemetry. After investigating with Fly's team, we identified the root cause as a bad interaction between a recent guest kernel update on Fly's newer machines and an upstream Cloud Hypervisor bug \([cloud-hypervisor#7672](https://github.com/cloud-hypervisor/cloud-hypervisor/issues/7672)\) affecting log writes from inside the VM. We mitigated by disabling the affected logging paths, and Fly has since rolled out a hypervisor-side patch, fully resolving the issue. No data was lost. Sorry for the disruption.

• Started

  May 11, 2026 · 3:05 PM

• Resolved

  May 11, 2026 · 6:22 PM

• Duration

  3h 16m

• Severity

  Major

• ◐

  Investigating

  May 11 · 3:05 PM Upstash

  Some databases may experience increased latency or timeouts in Fly.io’s FRA region.

• ◐

  Investigating

  May 11 · 3:07 PM Upstash

  We are continuing to investigate the issue.

• ◐

  Investigating

  May 11 · 5:19 PM Upstash

  We are working with Fly team to investigate the root cause.

• ✓

  Resolved

  May 11 · 6:22 PM Upstash

  The incident has been resolved. We are working with Fly team on RCA.

• ✓

  Postmortem

  May 15 · 12:49 PM Upstash

  On May 12th and 13th at various times, a subset of Upstash Redis instances on [Fly.io](http://Fly.io) experienced intermittent hangs and elevated error rates. The Redis process would stall inside a logging syscall — alive but not making progress — which made the issue hard to spot from our usual telemetry. After investigating with Fly's team, we identified the root cause as a bad interaction between a recent guest kernel update on Fly's newer machines and an upstream Cloud Hypervisor bug \([cloud-hypervisor#7672](https://github.com/cloud-hypervisor/cloud-hypervisor/issues/7672)\) affecting log writes from inside the VM. We mitigated by disabling the affected logging paths, and Fly has since rolled out a hypervisor-side patch, fully resolving the issue. No data was lost. Sorry for the disruption.